SPM Lukisan Kejuruteraan cheat sheet

Perpendicular bisector: with the compass set wider than half the segment, draw intersecting arcs from both endpoints; the line through the two intersections is perpendicular to the segment at its midpoint.

Bisecting an angle: strike an arc from the vertex to cut both arms, then strike equal arcs from those two cut points; the line from the vertex through the arc intersection bisects the angle.

To divide a line into n equal parts: draw an auxiliary line at any convenient angle, step off n equal compass divisions, join the last division to the far endpoint, then draw parallels through each division point.

Regular hexagon in a circle: the compass setting equal to the circumradius steps exactly six times around the circle; connect alternate vertices for an equilateral triangle.

Regular pentagon: construct by stepping the chord equal to the side of the pentagon (side = 1.1756 x R for circumradius R) or by the standard 72-degree radial division method.

Tangents to a circle from an external point: bisect the line joining the point to the centre, draw a semicircle on it, and the intersections with the given circle are the tangent points.

An ellipse can be drawn by the concentric-circle method (project points from the major and minor auxiliary circles) or the trammel/foci method where PF1 + PF2 = major axis length.

A fillet or round is a tangent arc: locate its centre at distance r from each of the two lines it joins, then draw the arc between the tangent points.

Construction lines are drawn light and thin (about 0.3 mm, grade H or 2H) and are not erased until the finished outline in grade B or HB is complete.

First-angle projection places the object between observer and plane: the view seen from the front is drawn above the front view's position in the layout, and the left-side view is drawn on the right.

Third-angle projection places the plane between observer and object: the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol distinguishes the two systems.

The front view is chosen to show the greatest extent and the fewest hidden features; height appears in front and side views, width in front and top views, depth in side and top views.

Hidden detail is drawn as short dashes of equal length with gaps about one third of the dash length; centre lines are long-short-long chains that extend slightly beyond the outline.

Adjacent views must align: projectors run perpendicular between views so widths and heights transfer exactly; a 45-degree mitre line transfers depth from top to side view.

Visible outlines use a thick continuous line (about 0.7 mm, grade B or HB); hidden lines are medium, dimension and projection lines thin continuous.

A section plane is indicated by a chain line with thick ends and arrows showing the viewing direction; the resulting view is labelled A-A or similar.

When a feature appears as a circle in one view, it appears as a rectangle of width equal to the diameter in the perpendicular view, so a single circle plus one rectangle defines a cylinder.

Isometric axes are 120 degrees apart: one vertical axis and two receding at 30 degrees above the horizontal; all three isometric lengths are drawn full scale (isometric drawing, not true projection).

True isometric projection foreshortens each axis to about 0.816 of true length; isometric drawing uses full lengths along the axes, giving a figure about 1.22 times the projected size.

Non-isometric lines are never measured directly: locate their endpoints on the isometric axes and join them, or enclose the face in an isometric box and transfer the points.

Circles on isometric faces become ellipses with major axis about 1.22 x D and minor axis about 0.71 x D, the major axis being perpendicular to the axis of the cylinder.

The four-centre approximate ellipse uses the corners of the isometric square of the circle: the two near corners are centres for the large arcs, the intersections of diagonals with the square sides for the small arcs.

Cavalier oblique uses full-scale receding lines; cabinet oblique halves them (0.5); the receding axis is normally 45 degrees, and the face parallel to the picture plane is drawn true shape.

In oblique drawing choose the face with the most circular or irregular detail as the true-shape front face to avoid drawing ellipses.

Isometric sketching is built from an isometric box or grid: block the overall envelope first, then cut away or add features in axis order.

Cutting-plane hatching is drawn as thin continuous lines at 45 degrees, equally spaced; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

The same part is hatched in the same direction and spacing throughout an assembly drawing, so hatching identifies a single component across the view.

Full section: the cutting plane passes completely through the object; half section: it passes halfway, giving half in section and half in outside view, used for symmetrical parts.

Offset (stepped) sections use a cutting plane stepped through features not in one plane; the change of plane is shown by a thick line in the section view, not by a line in the sectioned area.

Revolution sections show a true cross-section rotated into the view; removed sections are drawn outside the view and labelled with the cutting-plane letters.

Standard parts such as shafts, bolts, nuts, rivets, keys and pins are not sectioned when cut longitudinally, nor are ribs, webs and spokes cut lengthwise (they are shown unsectioned to avoid false solidity).

Hidden lines are normally omitted from sectioned views unless needed for clarity; visible edges behind the cutting plane are drawn as full lines.

Section lines stop at the outline; hatch spacing should be even and not so dense that it reads as solid black, and the section plane line uses a chain line with thick ends.

Dimension lines are thin continuous lines terminated by arrowheads, placed outside the extension lines; the value is written above and parallel to the dimension line, readable from the bottom or right of the sheet.

Extension lines start about 1 mm clear of the outline and extend about 2-3 mm beyond the dimension line; they never cross dimension lines and never replace an outline.

Dimension the feature once only, on the view where it appears as a true shape; do not repeat a dimension in another view and do not close a chain of dimensions on a finished surface unless required.

Limit dimensions state the maximum and minimum sizes (for example 25.00 and 24.95); tolerance is the difference between them, and the basic size is the nominal size from which deviations are measured.

A fit is described by hole basis H (lower deviation zero) or shaft basis h; clearance fits (H7/g6, H7/h6), interference fits (H7/p6) and transition fits (H7/k6, H7/js6) follow ISO 286.

Geometrical tolerances use a rectangular frame with the characteristic symbol, tolerance value and datum letter; flatness, straightness and circularity need no datum, while perpendicularity, parallelism and position do.

Surface roughness Ra is the arithmetic mean deviation in micrometres; the surface texture symbol carries the Ra value above the tick and a machining note where required, and a circle in the symbol means no material removal is permitted.

Diameter is prefixed by the symbol for diameter, radius by R, spherical radius by SR, and a square section by the square symbol; a dimension to a centre line uses the diameter symbol.

ISO metric thread designation: M followed by nominal diameter and pitch (M10 x 1.5); coarse pitch is omitted, so M10 means coarse 1.5 mm pitch.

Thread drawing convention: the crest is a thick continuous line, the root a thin continuous line at about 0.85 of the major diameter; in end view the root is a thin three-quarter circle.

A bolt, nut and washer assembly is drawn with the nut and washer in front of the joined parts, the bolt shank in the clearance hole, and the tapped hole shown with hidden root lines.

Keys and keyways: the key width equals the shaft keyway width, half the key sits in the shaft and half in the hub; a Woodruff key sits in a semicircular seat.

Rolling bearings are shown as simplified rectangles with the bore, outside diameter and width; the designation (for example 6205) encodes series and bore size (bore = 5 x last two digits for 04 and above).

Assembly drawing conventions: parts are numbered with leader lines to balloons, a parts list gives item, description, quantity and material, and only overall and fitting dimensions are given.

Welding symbols sit on a reference line with the arrow side below and the other side above; the fillet weld symbol is a right triangle and the size is written to its left.

Gears are represented by the addendum circle (thick), pitch circle (chain line) and root circle (thin); the module m = pitch diameter / number of teeth.

Model space holds full-size geometry; paper space (layout) holds the title block and viewports at a plotted scale, so the model is never scaled down to fit the sheet.

Object snapping (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforces geometric accuracy; grid snap and ortho constrain the cursor to fixed increments or to horizontal and vertical directions.

Layers carry colour, line type, line weight and on/off/freeze/lock states; drawing outlines, hidden lines, centre lines and dimensions on separate layers lets plotting follow layer settings.

A block is a named group inserted by reference; editing the block definition updates every insertion, while an exploded copy loses that link.

Dimension styles store arrow size, text height, extension-line offset and precision, so one style change reformats all associative dimensions.

Hatching uses an associative boundary: move the boundary and the hatch updates; unassociated hatch must be redefined.

CAD file exchange formats: DXF for editable interchange between systems, DWG for native AutoCAD data, and PDF or DWF for issue and review.

Plot scale is expressed as a ratio such as 1:2 or 1:5; a scale of 2:1 enlarges, and the scale factor in paper space viewports sets the printed size.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.

Perpendicular bisector: with the compass set wider than half the segment, draw intersecting arcs from both endpoints; the line through the two intersections is perpendicular to the segment at its midpoint.

Bisecting an angle: strike an arc from the vertex to cut both arms, then strike equal arcs from those two cut points; the line from the vertex through the arc intersection bisects the angle.

To divide a line into n equal parts: draw an auxiliary line at any convenient angle, step off n equal compass divisions, join the last division to the far endpoint, then draw parallels through each division point.

Regular hexagon in a circle: the compass setting equal to the circumradius steps exactly six times around the circle; connect alternate vertices for an equilateral triangle.

Regular pentagon: construct by stepping the chord equal to the side of the pentagon (side = 1.1756 x R for circumradius R) or by the standard 72-degree radial division method.

Tangents to a circle from an external point: bisect the line joining the point to the centre, draw a semicircle on it, and the intersections with the given circle are the tangent points.

An ellipse can be drawn by the concentric-circle method (project points from the major and minor auxiliary circles) or the trammel/foci method where PF1 + PF2 = major axis length.

A fillet or round is a tangent arc: locate its centre at distance r from each of the two lines it joins, then draw the arc between the tangent points.

Construction lines are drawn light and thin (about 0.3 mm, grade H or 2H) and are not erased until the finished outline in grade B or HB is complete.

First-angle projection places the object between observer and plane: the view seen from the front is drawn above the front view's position in the layout, and the left-side view is drawn on the right.

Third-angle projection places the plane between observer and object: the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol distinguishes the two systems.

The front view is chosen to show the greatest extent and the fewest hidden features; height appears in front and side views, width in front and top views, depth in side and top views.

Hidden detail is drawn as short dashes of equal length with gaps about one third of the dash length; centre lines are long-short-long chains that extend slightly beyond the outline.

Adjacent views must align: projectors run perpendicular between views so widths and heights transfer exactly; a 45-degree mitre line transfers depth from top to side view.

Visible outlines use a thick continuous line (about 0.7 mm, grade B or HB); hidden lines are medium, dimension and projection lines thin continuous.

A section plane is indicated by a chain line with thick ends and arrows showing the viewing direction; the resulting view is labelled A-A or similar.

When a feature appears as a circle in one view, it appears as a rectangle of width equal to the diameter in the perpendicular view, so a single circle plus one rectangle defines a cylinder.

Isometric axes are 120 degrees apart: one vertical axis and two receding at 30 degrees above the horizontal; all three isometric lengths are drawn full scale (isometric drawing, not true projection).

True isometric projection foreshortens each axis to about 0.816 of true length; isometric drawing uses full lengths along the axes, giving a figure about 1.22 times the projected size.

Non-isometric lines are never measured directly: locate their endpoints on the isometric axes and join them, or enclose the face in an isometric box and transfer the points.

Circles on isometric faces become ellipses with major axis about 1.22 x D and minor axis about 0.71 x D, the major axis being perpendicular to the axis of the cylinder.

The four-centre approximate ellipse uses the corners of the isometric square of the circle: the two near corners are centres for the large arcs, the intersections of diagonals with the square sides for the small arcs.

Cavalier oblique uses full-scale receding lines; cabinet oblique halves them (0.5); the receding axis is normally 45 degrees, and the face parallel to the picture plane is drawn true shape.

In oblique drawing choose the face with the most circular or irregular detail as the true-shape front face to avoid drawing ellipses.

Isometric sketching is built from an isometric box or grid: block the overall envelope first, then cut away or add features in axis order.

Cutting-plane hatching is drawn as thin continuous lines at 45 degrees, equally spaced; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

The same part is hatched in the same direction and spacing throughout an assembly drawing, so hatching identifies a single component across the view.

Full section: the cutting plane passes completely through the object; half section: it passes halfway, giving half in section and half in outside view, used for symmetrical parts.

Offset (stepped) sections use a cutting plane stepped through features not in one plane; the change of plane is shown by a thick line in the section view, not by a line in the sectioned area.

Revolution sections show a true cross-section rotated into the view; removed sections are drawn outside the view and labelled with the cutting-plane letters.

Standard parts such as shafts, bolts, nuts, rivets, keys and pins are not sectioned when cut longitudinally, nor are ribs, webs and spokes cut lengthwise (they are shown unsectioned to avoid false solidity).

Hidden lines are normally omitted from sectioned views unless needed for clarity; visible edges behind the cutting plane are drawn as full lines.

Section lines stop at the outline; hatch spacing should be even and not so dense that it reads as solid black, and the section plane line uses a chain line with thick ends.

Dimension lines are thin continuous lines terminated by arrowheads, placed outside the extension lines; the value is written above and parallel to the dimension line, readable from the bottom or right of the sheet.

Extension lines start about 1 mm clear of the outline and extend about 2-3 mm beyond the dimension line; they never cross dimension lines and never replace an outline.

Dimension the feature once only, on the view where it appears as a true shape; do not repeat a dimension in another view and do not close a chain of dimensions on a finished surface unless required.

Limit dimensions state the maximum and minimum sizes (for example 25.00 and 24.95); tolerance is the difference between them, and the basic size is the nominal size from which deviations are measured.

A fit is described by hole basis H (lower deviation zero) or shaft basis h; clearance fits (H7/g6, H7/h6), interference fits (H7/p6) and transition fits (H7/k6, H7/js6) follow ISO 286.

Geometrical tolerances use a rectangular frame with the characteristic symbol, tolerance value and datum letter; flatness, straightness and circularity need no datum, while perpendicularity, parallelism and position do.

Surface roughness Ra is the arithmetic mean deviation in micrometres; the surface texture symbol carries the Ra value above the tick and a machining note where required, and a circle in the symbol means no material removal is permitted.

Diameter is prefixed by the symbol for diameter, radius by R, spherical radius by SR, and a square section by the square symbol; a dimension to a centre line uses the diameter symbol.

ISO metric thread designation: M followed by nominal diameter and pitch (M10 x 1.5); coarse pitch is omitted, so M10 means coarse 1.5 mm pitch.

Thread drawing convention: the crest is a thick continuous line, the root a thin continuous line at about 0.85 of the major diameter; in end view the root is a thin three-quarter circle.

A bolt, nut and washer assembly is drawn with the nut and washer in front of the joined parts, the bolt shank in the clearance hole, and the tapped hole shown with hidden root lines.

Keys and keyways: the key width equals the shaft keyway width, half the key sits in the shaft and half in the hub; a Woodruff key sits in a semicircular seat.

Rolling bearings are shown as simplified rectangles with the bore, outside diameter and width; the designation (for example 6205) encodes series and bore size (bore = 5 x last two digits for 04 and above).

Assembly drawing conventions: parts are numbered with leader lines to balloons, a parts list gives item, description, quantity and material, and only overall and fitting dimensions are given.

Welding symbols sit on a reference line with the arrow side below and the other side above; the fillet weld symbol is a right triangle and the size is written to its left.

Gears are represented by the addendum circle (thick), pitch circle (chain line) and root circle (thin); the module m = pitch diameter / number of teeth.

Model space holds full-size geometry; paper space (layout) holds the title block and viewports at a plotted scale, so the model is never scaled down to fit the sheet.

Object snapping (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforces geometric accuracy; grid snap and ortho constrain the cursor to fixed increments or to horizontal and vertical directions.

Layers carry colour, line type, line weight and on/off/freeze/lock states; drawing outlines, hidden lines, centre lines and dimensions on separate layers lets plotting follow layer settings.

A block is a named group inserted by reference; editing the block definition updates every insertion, while an exploded copy loses that link.

Dimension styles store arrow size, text height, extension-line offset and precision, so one style change reformats all associative dimensions.

Hatching uses an associative boundary: move the boundary and the hatch updates; unassociated hatch must be redefined.

CAD file exchange formats: DXF for editable interchange between systems, DWG for native AutoCAD data, and PDF or DWF for issue and review.

Plot scale is expressed as a ratio such as 1:2 or 1:5; a scale of 2:1 enlarges, and the scale factor in paper space viewports sets the printed size.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.

Perpendicular bisector: with the compass set wider than half the segment, draw intersecting arcs from both endpoints; the line through the two intersections is perpendicular to the segment at its midpoint.

Bisecting an angle: strike an arc from the vertex to cut both arms, then strike equal arcs from those two cut points; the line from the vertex through the arc intersection bisects the angle.

To divide a line into n equal parts: draw an auxiliary line at any convenient angle, step off n equal compass divisions, join the last division to the far endpoint, then draw parallels through each division point.

Regular hexagon in a circle: the compass setting equal to the circumradius steps exactly six times around the circle; connect alternate vertices for an equilateral triangle.

Regular pentagon: construct by stepping the chord equal to the side of the pentagon (side = 1.1756 x R for circumradius R) or by the standard 72-degree radial division method.

Tangents to a circle from an external point: bisect the line joining the point to the centre, draw a semicircle on it, and the intersections with the given circle are the tangent points.

An ellipse can be drawn by the concentric-circle method (project points from the major and minor auxiliary circles) or the trammel/foci method where PF1 + PF2 = major axis length.

A fillet or round is a tangent arc: locate its centre at distance r from each of the two lines it joins, then draw the arc between the tangent points.

Construction lines are drawn light and thin (about 0.3 mm, grade H or 2H) and are not erased until the finished outline in grade B or HB is complete.

First-angle projection places the object between observer and plane: the view seen from the front is drawn above the front view's position in the layout, and the left-side view is drawn on the right.

Third-angle projection places the plane between observer and object: the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol distinguishes the two systems.

The front view is chosen to show the greatest extent and the fewest hidden features; height appears in front and side views, width in front and top views, depth in side and top views.

Hidden detail is drawn as short dashes of equal length with gaps about one third of the dash length; centre lines are long-short-long chains that extend slightly beyond the outline.

Adjacent views must align: projectors run perpendicular between views so widths and heights transfer exactly; a 45-degree mitre line transfers depth from top to side view.

Visible outlines use a thick continuous line (about 0.7 mm, grade B or HB); hidden lines are medium, dimension and projection lines thin continuous.

A section plane is indicated by a chain line with thick ends and arrows showing the viewing direction; the resulting view is labelled A-A or similar.

When a feature appears as a circle in one view, it appears as a rectangle of width equal to the diameter in the perpendicular view, so a single circle plus one rectangle defines a cylinder.

Isometric axes are 120 degrees apart: one vertical axis and two receding at 30 degrees above the horizontal; all three isometric lengths are drawn full scale (isometric drawing, not true projection).

True isometric projection foreshortens each axis to about 0.816 of true length; isometric drawing uses full lengths along the axes, giving a figure about 1.22 times the projected size.

Non-isometric lines are never measured directly: locate their endpoints on the isometric axes and join them, or enclose the face in an isometric box and transfer the points.

Circles on isometric faces become ellipses with major axis about 1.22 x D and minor axis about 0.71 x D, the major axis being perpendicular to the axis of the cylinder.

The four-centre approximate ellipse uses the corners of the isometric square of the circle: the two near corners are centres for the large arcs, the intersections of diagonals with the square sides for the small arcs.

Cavalier oblique uses full-scale receding lines; cabinet oblique halves them (0.5); the receding axis is normally 45 degrees, and the face parallel to the picture plane is drawn true shape.

In oblique drawing choose the face with the most circular or irregular detail as the true-shape front face to avoid drawing ellipses.

Isometric sketching is built from an isometric box or grid: block the overall envelope first, then cut away or add features in axis order.

Cutting-plane hatching is drawn as thin continuous lines at 45 degrees, equally spaced; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

The same part is hatched in the same direction and spacing throughout an assembly drawing, so hatching identifies a single component across the view.

Full section: the cutting plane passes completely through the object; half section: it passes halfway, giving half in section and half in outside view, used for symmetrical parts.

Offset (stepped) sections use a cutting plane stepped through features not in one plane; the change of plane is shown by a thick line in the section view, not by a line in the sectioned area.

Revolution sections show a true cross-section rotated into the view; removed sections are drawn outside the view and labelled with the cutting-plane letters.

Standard parts such as shafts, bolts, nuts, rivets, keys and pins are not sectioned when cut longitudinally, nor are ribs, webs and spokes cut lengthwise (they are shown unsectioned to avoid false solidity).

Hidden lines are normally omitted from sectioned views unless needed for clarity; visible edges behind the cutting plane are drawn as full lines.

Section lines stop at the outline; hatch spacing should be even and not so dense that it reads as solid black, and the section plane line uses a chain line with thick ends.

Dimension lines are thin continuous lines terminated by arrowheads, placed outside the extension lines; the value is written above and parallel to the dimension line, readable from the bottom or right of the sheet.

Extension lines start about 1 mm clear of the outline and extend about 2-3 mm beyond the dimension line; they never cross dimension lines and never replace an outline.

Dimension the feature once only, on the view where it appears as a true shape; do not repeat a dimension in another view and do not close a chain of dimensions on a finished surface unless required.

Limit dimensions state the maximum and minimum sizes (for example 25.00 and 24.95); tolerance is the difference between them, and the basic size is the nominal size from which deviations are measured.

A fit is described by hole basis H (lower deviation zero) or shaft basis h; clearance fits (H7/g6, H7/h6), interference fits (H7/p6) and transition fits (H7/k6, H7/js6) follow ISO 286.

Geometrical tolerances use a rectangular frame with the characteristic symbol, tolerance value and datum letter; flatness, straightness and circularity need no datum, while perpendicularity, parallelism and position do.

Surface roughness Ra is the arithmetic mean deviation in micrometres; the surface texture symbol carries the Ra value above the tick and a machining note where required, and a circle in the symbol means no material removal is permitted.

Diameter is prefixed by the symbol for diameter, radius by R, spherical radius by SR, and a square section by the square symbol; a dimension to a centre line uses the diameter symbol.

ISO metric thread designation: M followed by nominal diameter and pitch (M10 x 1.5); coarse pitch is omitted, so M10 means coarse 1.5 mm pitch.

Thread drawing convention: the crest is a thick continuous line, the root a thin continuous line at about 0.85 of the major diameter; in end view the root is a thin three-quarter circle.

A bolt, nut and washer assembly is drawn with the nut and washer in front of the joined parts, the bolt shank in the clearance hole, and the tapped hole shown with hidden root lines.

Keys and keyways: the key width equals the shaft keyway width, half the key sits in the shaft and half in the hub; a Woodruff key sits in a semicircular seat.

Rolling bearings are shown as simplified rectangles with the bore, outside diameter and width; the designation (for example 6205) encodes series and bore size (bore = 5 x last two digits for 04 and above).

Assembly drawing conventions: parts are numbered with leader lines to balloons, a parts list gives item, description, quantity and material, and only overall and fitting dimensions are given.

Welding symbols sit on a reference line with the arrow side below and the other side above; the fillet weld symbol is a right triangle and the size is written to its left.

Gears are represented by the addendum circle (thick), pitch circle (chain line) and root circle (thin); the module m = pitch diameter / number of teeth.

Model space holds full-size geometry; paper space (layout) holds the title block and viewports at a plotted scale, so the model is never scaled down to fit the sheet.

Object snapping (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforces geometric accuracy; grid snap and ortho constrain the cursor to fixed increments or to horizontal and vertical directions.

Layers carry colour, line type, line weight and on/off/freeze/lock states; drawing outlines, hidden lines, centre lines and dimensions on separate layers lets plotting follow layer settings.

A block is a named group inserted by reference; editing the block definition updates every insertion, while an exploded copy loses that link.

Dimension styles store arrow size, text height, extension-line offset and precision, so one style change reformats all associative dimensions.

Hatching uses an associative boundary: move the boundary and the hatch updates; unassociated hatch must be redefined.

CAD file exchange formats: DXF for editable interchange between systems, DWG for native AutoCAD data, and PDF or DWF for issue and review.

Plot scale is expressed as a ratio such as 1:2 or 1:5; a scale of 2:1 enlarges, and the scale factor in paper space viewports sets the printed size.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.

Perpendicular bisector: with the compass set wider than half the segment, draw intersecting arcs from both endpoints; the line through the two intersections is perpendicular to the segment at its midpoint.

Bisecting an angle: strike an arc from the vertex to cut both arms, then strike equal arcs from those two cut points; the line from the vertex through the arc intersection bisects the angle.

To divide a line into n equal parts: draw an auxiliary line at any convenient angle, step off n equal compass divisions, join the last division to the far endpoint, then draw parallels through each division point.

Regular hexagon in a circle: the compass setting equal to the circumradius steps exactly six times around the circle; connect alternate vertices for an equilateral triangle.

Regular pentagon: construct by stepping the chord equal to the side of the pentagon (side = 1.1756 x R for circumradius R) or by the standard 72-degree radial division method.

Tangents to a circle from an external point: bisect the line joining the point to the centre, draw a semicircle on it, and the intersections with the given circle are the tangent points.

An ellipse can be drawn by the concentric-circle method (project points from the major and minor auxiliary circles) or the trammel/foci method where PF1 + PF2 = major axis length.

A fillet or round is a tangent arc: locate its centre at distance r from each of the two lines it joins, then draw the arc between the tangent points.

Construction lines are drawn light and thin (about 0.3 mm, grade H or 2H) and are not erased until the finished outline in grade B or HB is complete.

First-angle projection places the object between observer and plane: the view seen from the front is drawn above the front view's position in the layout, and the left-side view is drawn on the right.

Third-angle projection places the plane between observer and object: the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol distinguishes the two systems.

The front view is chosen to show the greatest extent and the fewest hidden features; height appears in front and side views, width in front and top views, depth in side and top views.

Hidden detail is drawn as short dashes of equal length with gaps about one third of the dash length; centre lines are long-short-long chains that extend slightly beyond the outline.

Adjacent views must align: projectors run perpendicular between views so widths and heights transfer exactly; a 45-degree mitre line transfers depth from top to side view.

Visible outlines use a thick continuous line (about 0.7 mm, grade B or HB); hidden lines are medium, dimension and projection lines thin continuous.

A section plane is indicated by a chain line with thick ends and arrows showing the viewing direction; the resulting view is labelled A-A or similar.

When a feature appears as a circle in one view, it appears as a rectangle of width equal to the diameter in the perpendicular view, so a single circle plus one rectangle defines a cylinder.

Isometric axes are 120 degrees apart: one vertical axis and two receding at 30 degrees above the horizontal; all three isometric lengths are drawn full scale (isometric drawing, not true projection).

True isometric projection foreshortens each axis to about 0.816 of true length; isometric drawing uses full lengths along the axes, giving a figure about 1.22 times the projected size.

Non-isometric lines are never measured directly: locate their endpoints on the isometric axes and join them, or enclose the face in an isometric box and transfer the points.

Circles on isometric faces become ellipses with major axis about 1.22 x D and minor axis about 0.71 x D, the major axis being perpendicular to the axis of the cylinder.

The four-centre approximate ellipse uses the corners of the isometric square of the circle: the two near corners are centres for the large arcs, the intersections of diagonals with the square sides for the small arcs.

Cavalier oblique uses full-scale receding lines; cabinet oblique halves them (0.5); the receding axis is normally 45 degrees, and the face parallel to the picture plane is drawn true shape.

In oblique drawing choose the face with the most circular or irregular detail as the true-shape front face to avoid drawing ellipses.

Isometric sketching is built from an isometric box or grid: block the overall envelope first, then cut away or add features in axis order.

Cutting-plane hatching is drawn as thin continuous lines at 45 degrees, equally spaced; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

The same part is hatched in the same direction and spacing throughout an assembly drawing, so hatching identifies a single component across the view.

Full section: the cutting plane passes completely through the object; half section: it passes halfway, giving half in section and half in outside view, used for symmetrical parts.

Offset (stepped) sections use a cutting plane stepped through features not in one plane; the change of plane is shown by a thick line in the section view, not by a line in the sectioned area.

Revolution sections show a true cross-section rotated into the view; removed sections are drawn outside the view and labelled with the cutting-plane letters.

Standard parts such as shafts, bolts, nuts, rivets, keys and pins are not sectioned when cut longitudinally, nor are ribs, webs and spokes cut lengthwise (they are shown unsectioned to avoid false solidity).

Hidden lines are normally omitted from sectioned views unless needed for clarity; visible edges behind the cutting plane are drawn as full lines.

Section lines stop at the outline; hatch spacing should be even and not so dense that it reads as solid black, and the section plane line uses a chain line with thick ends.

Dimension lines are thin continuous lines terminated by arrowheads, placed outside the extension lines; the value is written above and parallel to the dimension line, readable from the bottom or right of the sheet.

Extension lines start about 1 mm clear of the outline and extend about 2-3 mm beyond the dimension line; they never cross dimension lines and never replace an outline.

Dimension the feature once only, on the view where it appears as a true shape; do not repeat a dimension in another view and do not close a chain of dimensions on a finished surface unless required.

Limit dimensions state the maximum and minimum sizes (for example 25.00 and 24.95); tolerance is the difference between them, and the basic size is the nominal size from which deviations are measured.

A fit is described by hole basis H (lower deviation zero) or shaft basis h; clearance fits (H7/g6, H7/h6), interference fits (H7/p6) and transition fits (H7/k6, H7/js6) follow ISO 286.

Geometrical tolerances use a rectangular frame with the characteristic symbol, tolerance value and datum letter; flatness, straightness and circularity need no datum, while perpendicularity, parallelism and position do.

Surface roughness Ra is the arithmetic mean deviation in micrometres; the surface texture symbol carries the Ra value above the tick and a machining note where required, and a circle in the symbol means no material removal is permitted.

Diameter is prefixed by the symbol for diameter, radius by R, spherical radius by SR, and a square section by the square symbol; a dimension to a centre line uses the diameter symbol.

ISO metric thread designation: M followed by nominal diameter and pitch (M10 x 1.5); coarse pitch is omitted, so M10 means coarse 1.5 mm pitch.

Thread drawing convention: the crest is a thick continuous line, the root a thin continuous line at about 0.85 of the major diameter; in end view the root is a thin three-quarter circle.

A bolt, nut and washer assembly is drawn with the nut and washer in front of the joined parts, the bolt shank in the clearance hole, and the tapped hole shown with hidden root lines.

Keys and keyways: the key width equals the shaft keyway width, half the key sits in the shaft and half in the hub; a Woodruff key sits in a semicircular seat.

Rolling bearings are shown as simplified rectangles with the bore, outside diameter and width; the designation (for example 6205) encodes series and bore size (bore = 5 x last two digits for 04 and above).

Assembly drawing conventions: parts are numbered with leader lines to balloons, a parts list gives item, description, quantity and material, and only overall and fitting dimensions are given.

Welding symbols sit on a reference line with the arrow side below and the other side above; the fillet weld symbol is a right triangle and the size is written to its left.

Gears are represented by the addendum circle (thick), pitch circle (chain line) and root circle (thin); the module m = pitch diameter / number of teeth.

Model space holds full-size geometry; paper space (layout) holds the title block and viewports at a plotted scale, so the model is never scaled down to fit the sheet.

Object snapping (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforces geometric accuracy; grid snap and ortho constrain the cursor to fixed increments or to horizontal and vertical directions.

Layers carry colour, line type, line weight and on/off/freeze/lock states; drawing outlines, hidden lines, centre lines and dimensions on separate layers lets plotting follow layer settings.

A block is a named group inserted by reference; editing the block definition updates every insertion, while an exploded copy loses that link.

Dimension styles store arrow size, text height, extension-line offset and precision, so one style change reformats all associative dimensions.

Hatching uses an associative boundary: move the boundary and the hatch updates; unassociated hatch must be redefined.

CAD file exchange formats: DXF for editable interchange between systems, DWG for native AutoCAD data, and PDF or DWF for issue and review.

Plot scale is expressed as a ratio such as 1:2 or 1:5; a scale of 2:1 enlarges, and the scale factor in paper space viewports sets the printed size.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.

Perpendicular bisector: with the compass set wider than half the segment, draw intersecting arcs from both endpoints; the line through the two intersections is perpendicular to the segment at its midpoint.

Bisecting an angle: strike an arc from the vertex to cut both arms, then strike equal arcs from those two cut points; the line from the vertex through the arc intersection bisects the angle.

To divide a line into n equal parts: draw an auxiliary line at any convenient angle, step off n equal compass divisions, join the last division to the far endpoint, then draw parallels through each division point.

Regular hexagon in a circle: the compass setting equal to the circumradius steps exactly six times around the circle; connect alternate vertices for an equilateral triangle.

Regular pentagon: construct by stepping the chord equal to the side of the pentagon (side = 1.1756 x R for circumradius R) or by the standard 72-degree radial division method.

Tangents to a circle from an external point: bisect the line joining the point to the centre, draw a semicircle on it, and the intersections with the given circle are the tangent points.

An ellipse can be drawn by the concentric-circle method (project points from the major and minor auxiliary circles) or the trammel/foci method where PF1 + PF2 = major axis length.

A fillet or round is a tangent arc: locate its centre at distance r from each of the two lines it joins, then draw the arc between the tangent points.

Construction lines are drawn light and thin (about 0.3 mm, grade H or 2H) and are not erased until the finished outline in grade B or HB is complete.

First-angle projection places the object between observer and plane: the view seen from the front is drawn above the front view's position in the layout, and the left-side view is drawn on the right.

Third-angle projection places the plane between observer and object: the top view sits above the front view and the right-side view sits to the right; the truncated-cone symbol distinguishes the two systems.

The front view is chosen to show the greatest extent and the fewest hidden features; height appears in front and side views, width in front and top views, depth in side and top views.

Hidden detail is drawn as short dashes of equal length with gaps about one third of the dash length; centre lines are long-short-long chains that extend slightly beyond the outline.

Adjacent views must align: projectors run perpendicular between views so widths and heights transfer exactly; a 45-degree mitre line transfers depth from top to side view.

Visible outlines use a thick continuous line (about 0.7 mm, grade B or HB); hidden lines are medium, dimension and projection lines thin continuous.

A section plane is indicated by a chain line with thick ends and arrows showing the viewing direction; the resulting view is labelled A-A or similar.

When a feature appears as a circle in one view, it appears as a rectangle of width equal to the diameter in the perpendicular view, so a single circle plus one rectangle defines a cylinder.

Isometric axes are 120 degrees apart: one vertical axis and two receding at 30 degrees above the horizontal; all three isometric lengths are drawn full scale (isometric drawing, not true projection).

True isometric projection foreshortens each axis to about 0.816 of true length; isometric drawing uses full lengths along the axes, giving a figure about 1.22 times the projected size.

Non-isometric lines are never measured directly: locate their endpoints on the isometric axes and join them, or enclose the face in an isometric box and transfer the points.

Circles on isometric faces become ellipses with major axis about 1.22 x D and minor axis about 0.71 x D, the major axis being perpendicular to the axis of the cylinder.

The four-centre approximate ellipse uses the corners of the isometric square of the circle: the two near corners are centres for the large arcs, the intersections of diagonals with the square sides for the small arcs.

Cavalier oblique uses full-scale receding lines; cabinet oblique halves them (0.5); the receding axis is normally 45 degrees, and the face parallel to the picture plane is drawn true shape.

In oblique drawing choose the face with the most circular or irregular detail as the true-shape front face to avoid drawing ellipses.

Isometric sketching is built from an isometric box or grid: block the overall envelope first, then cut away or add features in axis order.

Cutting-plane hatching is drawn as thin continuous lines at 45 degrees, equally spaced; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

The same part is hatched in the same direction and spacing throughout an assembly drawing, so hatching identifies a single component across the view.

Full section: the cutting plane passes completely through the object; half section: it passes halfway, giving half in section and half in outside view, used for symmetrical parts.

Offset (stepped) sections use a cutting plane stepped through features not in one plane; the change of plane is shown by a thick line in the section view, not by a line in the sectioned area.

Revolution sections show a true cross-section rotated into the view; removed sections are drawn outside the view and labelled with the cutting-plane letters.

Standard parts such as shafts, bolts, nuts, rivets, keys and pins are not sectioned when cut longitudinally, nor are ribs, webs and spokes cut lengthwise (they are shown unsectioned to avoid false solidity).

Hidden lines are normally omitted from sectioned views unless needed for clarity; visible edges behind the cutting plane are drawn as full lines.

Section lines stop at the outline; hatch spacing should be even and not so dense that it reads as solid black, and the section plane line uses a chain line with thick ends.

Dimension lines are thin continuous lines terminated by arrowheads, placed outside the extension lines; the value is written above and parallel to the dimension line, readable from the bottom or right of the sheet.

Extension lines start about 1 mm clear of the outline and extend about 2-3 mm beyond the dimension line; they never cross dimension lines and never replace an outline.

Dimension the feature once only, on the view where it appears as a true shape; do not repeat a dimension in another view and do not close a chain of dimensions on a finished surface unless required.

Limit dimensions state the maximum and minimum sizes (for example 25.00 and 24.95); tolerance is the difference between them, and the basic size is the nominal size from which deviations are measured.

A fit is described by hole basis H (lower deviation zero) or shaft basis h; clearance fits (H7/g6, H7/h6), interference fits (H7/p6) and transition fits (H7/k6, H7/js6) follow ISO 286.

Geometrical tolerances use a rectangular frame with the characteristic symbol, tolerance value and datum letter; flatness, straightness and circularity need no datum, while perpendicularity, parallelism and position do.

Surface roughness Ra is the arithmetic mean deviation in micrometres; the surface texture symbol carries the Ra value above the tick and a machining note where required, and a circle in the symbol means no material removal is permitted.

Diameter is prefixed by the symbol for diameter, radius by R, spherical radius by SR, and a square section by the square symbol; a dimension to a centre line uses the diameter symbol.

ISO metric thread designation: M followed by nominal diameter and pitch (M10 x 1.5); coarse pitch is omitted, so M10 means coarse 1.5 mm pitch.

Thread drawing convention: the crest is a thick continuous line, the root a thin continuous line at about 0.85 of the major diameter; in end view the root is a thin three-quarter circle.

A bolt, nut and washer assembly is drawn with the nut and washer in front of the joined parts, the bolt shank in the clearance hole, and the tapped hole shown with hidden root lines.

Keys and keyways: the key width equals the shaft keyway width, half the key sits in the shaft and half in the hub; a Woodruff key sits in a semicircular seat.

Rolling bearings are shown as simplified rectangles with the bore, outside diameter and width; the designation (for example 6205) encodes series and bore size (bore = 5 x last two digits for 04 and above).

Assembly drawing conventions: parts are numbered with leader lines to balloons, a parts list gives item, description, quantity and material, and only overall and fitting dimensions are given.

Welding symbols sit on a reference line with the arrow side below and the other side above; the fillet weld symbol is a right triangle and the size is written to its left.

Gears are represented by the addendum circle (thick), pitch circle (chain line) and root circle (thin); the module m = pitch diameter / number of teeth.

Model space holds full-size geometry; paper space (layout) holds the title block and viewports at a plotted scale, so the model is never scaled down to fit the sheet.

Object snapping (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforces geometric accuracy; grid snap and ortho constrain the cursor to fixed increments or to horizontal and vertical directions.

Layers carry colour, line type, line weight and on/off/freeze/lock states; drawing outlines, hidden lines, centre lines and dimensions on separate layers lets plotting follow layer settings.

A block is a named group inserted by reference; editing the block definition updates every insertion, while an exploded copy loses that link.

Dimension styles store arrow size, text height, extension-line offset and precision, so one style change reformats all associative dimensions.

Hatching uses an associative boundary: move the boundary and the hatch updates; unassociated hatch must be redefined.

CAD file exchange formats: DXF for editable interchange between systems, DWG for native AutoCAD data, and PDF or DWF for issue and review.

Plot scale is expressed as a ratio such as 1:2 or 1:5; a scale of 2:1 enlarges, and the scale factor in paper space viewports sets the printed size.

ISO 5457 defines sheet sizes: A0 is 841 x 1189 mm with an area of 1 square metre, and each subsequent size halves the longer side, so A4 is 210 x 297 mm.

The title block sits in the bottom right corner and records drawing number, title, scale, projection symbol, material, date, drawn and checked by, and revision.

Line groups by ISO 128: thick continuous for visible outlines (0.5-0.7 mm), thin continuous for dimensions and hatching (about half the thick width), dashed for hidden, chain for centre lines.

Lettering is upright or sloping capital letters, with a height of at least 2.5 mm for dimensions and a ratio of height to stroke width of about 14:1 for type B lettering.

The projection symbol uses a truncated cone: in first angle the small circle is on the left of the trapezium, in third angle on the right, when viewed from the front.

Drawing scales: preferred scales are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 and enlargements 2:1, 5:1, 10:1; the scale is stated in the title block and never measured from a print.

Safety practice: never use compasses or dividers without a sharp point and a firm grip, keep blades and cutters sheathed when not in use, and cut with a cutting mat and a steel rule, never towards the body.

Professional practice: drawings are controlled documents, so revisions are recorded in a revision block with a description, date and initials, and superseded copies are withdrawn.

Drawing frames leave a filing margin of 20 mm on the left edge and 10 mm on the other three edges for A4 to A0 sizes.

Centre marks and centre lines extend 2-3 mm past the outline; a centre line may be used as a dimension line where it defines a pitch circle.

Sections and detail views are labelled in capital letters (A-A, DETAIL B) and cross-referenced to the parent view with the same letter.

Geometrical tolerance symbols: straightness is a horizontal line, flatness a parallelogram, circularity a circle, cylindricity a circle between two parallel lines, and position a circle with a cross.

First-angle and third-angle symbols are never both shown; the chosen projection system governs every view on the sheet.

Standard abbreviations on drawings include DIA for diameter, R for radius, CHAM for chamfer, THK for thickness, and REF for reference dimension.

Ergonomic and safety rule for drawing offices: keep the drawing board tilted about 15-20 degrees, light from the left for right-handed users, and store drawing instruments in a case to protect points.