A term of plywood for a school workshop
Thirty six pupils, two projects each, two hundred and sixteen small parts, and a materials budget that was set in July and cannot move. The parts here are easy. The problem was that they were being cut eleven weeks apart.
The job
A design and technology department running two projects across an autumn term with a year group of thirty six. Everything comes out of 12 mm birch faced plywood on 2440 by 1220 sheets.
Project one is a tool tote, 400 long by 180 wide by 140 high, with the sides lapping over the ends so the ends come out at 156. Project two is a clock face. Per pupil that is five pieces for the tote and one for the clock, which across the year group comes to:
- 72 tote sides at 400 by 140
- 72 tote ends at 156 by 140
- 36 tote bases at 400 by 180
- 36 clock faces at 200 by 200
216 parts, 9.6 square metres. Not one of them is difficult. There are just a lot of them, and they are small, which is exactly the case where cutting as you go quietly eats a term's budget.
How it was being done before
The technician cut for the lesson in front of them. Week three needs tote sides, so a sheet goes on the saw and tote sides come off it until there are enough, and the rest of the sheet goes on the rack. Week nine needs clock faces, so another sheet comes off the rack, and it is rarely the same one.
Nobody is doing anything wrong. It is the only way to work when the parts list for week nine does not exist yet in week three. But it means every sheet is cut for one part type, and a sheet cut for 400 by 140 sides leaves a strip that nothing in week three wants.
Six sheets went through the workshop for this year group. Against 9.6 square metres of finished parts that is 46.0 per cent waste, and most of it was standing on the rack in pieces too small to be worth keeping and too big to throw away without feeling bad about it.
What changed
The whole term went into one parts list before the term started. Both projects, all thirty six pupils, one list. That is the only real change, and it is a scheduling change rather than a software one. Cut Solver's part is simply that it can hold two hundred and sixteen parts without anyone losing track.
Settings were a 3.2 mm kerf and a 10 mm trim. Birch ply has a face grain but nothing here is show wood, so parts were left free to turn.
Four sheets, cut in one afternoon in September, boxed and labelled by project.
Job sheet
- Material12 mm birch plywood
- Sheet size2440 x 1220
- Sheet area2.977 m2
- Parts216
- Part area9.6 m2
- Kerf3.2 mm
- Edge trim10 mm
- GrainFree to turn
- Sheets before6
- Sheets after4
The layout
Four sheets holding fifty six, forty one, forty four and seventy five parts. Small parts nest well, which is the whole reason batching them matters.
The result
Four sheets instead of six. Waste down from 46.0 per cent to 19.1 per cent, which for parts this small is about as good as sheet goods get. Two sheets is 6.0 square metres, and on a department budget that is a class set of something else.
The second effect mattered more to the technician than the first. Cutting a term in one afternoon and boxing the parts by project meant no sheet handling during the term at all, and no lesson where the saw was in use while a class waited.
The catch
Batching a term only works if the term is actually decided in advance. If a project changes in week six, you have a box of parts for a project nobody is building. The department now keeps one project fixed and one flexible, and only the fixed one gets batched.
The other catch is storage. Two hundred and sixteen small plywood parts take up a shelf, and they need labelling properly or you have simply moved the problem. The labels printed on the diagram get written onto the boxes, not the parts.
How long it took
Building the list took about twenty five minutes, and quantity is the only field that changes between year groups, so the file is now reused each September. The layout ran in about a second. Cutting four sheets took an afternoon, which is roughly what six sheets had taken spread across the term, except it was one afternoon instead of six interruptions.
The department uses the same file to work out how many sheets to order before the budget is committed, which turned out to be the part they valued most.
Small parts, big saving, every time
The smaller the parts, the more batching wins, because small parts fill the awkward corners that big parts leave. It is the opposite of intuition, which says small parts are fiddly and not worth planning.
The offcuts are worth keeping here
Four sheets of 12 mm birch leaves offcuts that are ideal for the next year's prototypes. Logging them beats stacking them, which is the argument in reusing offcuts.
The other five examples
Every job here is written up the same way, with the sheet count before, the sheet count after and the time it took.
- Eighteen kitchen carcasses from melamineKitchen fitting. 108 parts, 13 sheets down to 11.
- Acrylic letters nested for a sign shopSignmaking. 41 letters and roundels onto a single sheet.
- A sideboard cut with the grain running one wayFurniture making. 14 grain locked parts, 4 sheets down to 3.
- Marine ply for a small launchBoatbuilding. Scarfed hull pieces, 10 sheets down to 6.
- Engineered oak floor cut from lengthsFlooring. 81 pieces from 2200 mm boards, 64 down to 58.
Read on
The settings behind this job, and how to price the next one.