Register cutting on a drifting guillotine: diagnosing a 4 mm border error on 500 invitation cards
A 90 cm manual guillotine has been in use for four years in a workshop where one operator works from a wheelchair at a raised table. The unit accepts an order for 500 invitation cards, finished size 105 × 148 mm, printed four-up on 320 × 450 mm coated sheets with a 12 mm gold border printed from the trim line on all four sides. The customer will reject any card whose border varies by more than 1 mm from side to side. The operator sets the back gauge by eye against the printed scale, cuts the sheet into four strips, then cuts each strip to length. After 150 cards the owner finds the left border measures 10 mm and the right border 14 mm; the back gauge, checked against a steel rule over 100 mm of travel, reads 0.8 mm short. The machine has no false clamp, and the top three sheets of every pile show clamp marks. Delivery is in five days and the printed sheets cannot be reprinted in time.
1. Find the likely source of the uneven border and state the evidence you would collect before blaming the operator.
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Do not start with the operator. Measure the system in this order, because a 4 mm split means the trim line sits 2 mm off the printed centre - and no single fault listed in the setup explains 2 mm on its own.
- The gauge. 0.8 mm per 100 mm is a 0.8% lead. Over a 148 mm cut that is about 1.2 mm, and over 105 mm about 0.85 mm - real, but only part of the error.
- The sheet. Measure both diagonals of five untrimmed sheets. A difference above 0.5 mm means the sheet is out of square, so one straight cut cannot produce four equal borders.
- The print. Measure the border at all four corners of an untrimmed sheet. If the printed image is already 1 mm off-centre on the sheet, no cutting sequence can fix it - the job must be cut from printed register marks, not from the sheet edge.
- The first trim. Check whether the first cut actually removed the trim line or removed 2 mm of border. This is the commonest cause of a 10/14 split and is invisible on the finished card.
- The operator's method. Setting a gauge "by eye" against a printed scale on a machine with a known lead adds setting error on top of mechanical drift.
Only after these five checks can responsibility be assigned, and the corrective action differs for each cause.
2. Set out a cutting sequence, a jig and an inspection rule that will bring the remaining cards within tolerance, and state the tolerance you would promise.
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Sequence (reference first, measure second, cut third):
- Re-zero the back gauge or fit a positive mechanical stop; mark the corrected setting on the machine and record it.
- Take one sheet, find a printed register mark or the printed border, and make the head trim only. Never use the untrimmed sheet edge as the datum.
- Rotate the sheet 180°, cut the opposite edge to finished size using a cut hardboard spacer of the exact finished dimension as the stop.
- Turn 90° and repeat for the other two edges. Cut strips in lifts of no more than 25 sheets of coated stock.
Jig: a 3 mm hardboard template with a square corner and a stop batten clamped to the table gives a repeatable datum that a one-handed operator can locate against without measuring each time.
Clamp marks: place a waste sheet on top and bottom of every lift, reduce clamp pressure to the minimum that holds the pile, and keep the pile square before clamping.
Inspection: check every 25th card with a go/no-go gauge made from card - a 11.5 mm slot and a 12.5 mm slot. If a card fails either slot, stop and re-zero the gauge.
Tolerance promised: 12 mm ± 0.5 mm, which is tighter than the customer's ±1 mm and leaves room for the gauge lead between re-zeroings.
3. What would you do with the 150 cards already cut at 10 mm and 14 mm, and how would you report the loss?
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Can they be reworked? Trimming 2 mm off the 10 mm edge would make both borders 12 mm, but the finished size would fall to 103 × 148 mm - outside the 105 × 148 mm specification and visibly short against the other cards. Unless the customer gives written approval for a 103 × 148 mm size, reworking is not permitted, because a mixed batch of two sizes is worse than a short delivery.
Options, in order of preference:
- Ask the customer in writing whether the shorter size is acceptable for a reduced price, provided the border becomes 12/12 mm and every card in the batch is the same size.
- Use them as the workshop's own samples and enquiry cards - they carry the customer's gold border, so get permission before showing them.
- Sell as seconds locally, priced at material cost only.
Reporting: 150 of 500 cards is 30% of the order. The loss is the printed sheet cost plus the cutting labour for those sheets, not the selling price. Record the cause (gauge lead plus datum error), the corrective setting, and the inspection rule in the job card so the next coated-stock job starts from the corrected gauge. Also note that clamp marks on the top three sheets were a separate, avoidable defect and that a false clamp or waste-sheet practice would have prevented them; raise this with the owner as a machine-accessory purchase, not as an operator fault.