Out-of-Square Kitchen Base Run
Your crew is setting a 12 ft 4 in. run of base cabinets in a remodeled 1930s kitchen. The left wall meets the back wall at 88 degrees, the right wall at 91 degrees; the floor drops 5/8 in. from left to right. The cabinet run ends at a doorway casing on the right, leaving a 2 in. gap to the wall. The countertop will be 25 in. deep with a 1 1/2 in. overhang. The homeowner wants no visible filler on the face. You have a laser level, 6 ft spirit level, tape, framing square, and shims. The cabinets are frameless with 3/4 in. melamine boxes and adjustable legs. The first cabinet is a 30 in. sink base; the rest are 24 in. drawers. The wall is drywall over old plaster, and studs are 24 in. on center.
1. Before setting any cabinet, how do you establish a square reference line and decide where the run should start? Show the checks and calculations.
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Establish a level datum first. Find the highest floor point under the run with a straightedge and level; mark a line 34 1/2 in. above it for the standard base height. If the floor drops 5/8 in., shim all other cabinets up to that line rather than lowering the high cabinet.
Create a straight front-face line. Because the left wall is 88 degrees, a line squared to that wall will drift relative to the back wall. Snap a line representing the cabinet fronts parallel to the back wall at the required depth, then check it with a 3-4-5 triangle, such as 36 in. by 48 in. by 60 in., from the left wall. Measure from the snapped line to the back wall at both ends and at mid-run. If the back wall is bowed, use the cabinet backs as the reference and plan a scribe filler at the left wall.
Start at the left corner but do not bury the error. Set the first cabinet so its front edge is on the snapped line, then scribe the 2 in. filler to the 88 degree wall. Do not force the cabinet out of square. After clamping the first two cabinets, compare diagonals; equal diagonals confirm the boxes are not racked.
2. How do you handle the 2 in. gap at the door casing and the 5/8 in. floor drop while keeping cabinet faces aligned?
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At the casing: do not center a 2 in. filler as a visible strip. Use a scribe filler set slightly back from the door faces or a return molding, and scribe its edge to the casing. The cabinet face line stays straight; the filler absorbs the 91 degree angle and casing irregularity. If the gap is exactly 2 in., rip the filler 1/8 in. oversize and plane or scribe it to fit.
At the floor: set adjustable legs to the highest point. Where the floor is low, extend the legs and add shims under the leg pads so the cabinet is supported, not hanging from screws. Run a straightedge across the tops of adjacent cabinets and shim until the front edges are flush within 1/32 in. Attach the toe kick after the cabinets are level and scribe it to the floor so it follows the 5/8 in. slope without gaps. Do not use the toe kick to pull the cabinet down.
3. What measurements do you give the countertop fabricator to account for the out-of-square walls?
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Give a template, not just a length. Record: the back-wall length at counter height; the front-edge length at the 25 in. depth plus 1 1/2 in. overhang; the left and right end angles; and both diagonals from the left-back corner to the right-front corner and vice versa. If the walls are 88 and 91 degrees, the front and back dimensions differ; a rectangular top cut to the back length will either rock or leave a tapered overhang. Note the sink centerline and the 2 in. door casing clearance. A 1/4 in. hardboard template scribed to the walls is best; mark the front edge and overhang on it. Tell the fabricator which edge is scribed and where the top must be removable. Check the finished top against the cabinet fronts before setting it; the overhang should be uniform.