Optimizing Materials Versus Optimizing Time

      A small non-CNC shop considers whether it makes more sense to process more or fewer cabinets at a time. June 4, 2009

Question
I own a six man cabinet shop. We have been in business for a year and a half. We make high end cabinets - wood interiors, soft close doors and drawers and completely custom. On the tablesaw we currently cut the whole phase at one time. I am questioning if we should cut less cabinets at one time. We currently cut the whole job to save sheetgoods. Is it better to cut only what we can assemble in a day or to cut the whole job and save sheetgoods?

Forum Responses
(Cabinetmaking Forum)
From contributor J:
I don t really understand your question. Who would know better than you in your shop what works? I canít imagine how you would save sheetgoods either way. A 35 sheet job is a 35 sheet job whether you slice it all up in one day or several. In my operation no cabinets are cut out until the faceframes and doors, drawers, etc. have been completed. Euro style is just the opposite (for me anyway).



From contributor S:
I hope this will be easy to follow. When I was working in a similar sized shop (six to seven man shop) we would start cutting and would feed the next operation (point to point) which would then feed the next operation (edgeband) which would then feed the next operation (dowelling) which would feed the next operation (assembly) and so on. When the saw operator loaded one cart he started passing parts to the next operation and continued to cut parts until the next cart was filled and then passed that cart along. Each machine operator (or stage) would load one cart and start feeding the next stage. This method should ensure that everyone is working all the time. If someone down the line is not working and waiting for parts one of the processes earlier on is causing a bottleneck. Once you identify the bottleneck, you can take action to eliminate/reduce it and increase your production capacity. Continue to do this until you have eliminated/reduced all your bottlenecks.

A good saw operator should be able to "save" sheet goods. If you cut all at once or in stages your waste factor should be the same. You aren't changing what you are cutting you are only changing when you are cutting, this should have no affect on waste. With six men in the shop you should be trying to make any given part go from the saw to final assembly and out the door without waiting to be processed at any point.

Parts that need more operations (sides that need to be drilled and edgebanded, etc.) get cut first and are the first to start moving along. Parts that need less operations (shelves that just get edgebanding, etc.) get cut next and are second to start moving along. Parts that require no other operations (backs, etc.) get cut last and are last to move along. All the parts for a particular cabinet should arrive at assemble at about the same time. This is all dependent upon your definition of "completely custom." If "completely custom" means no two parts are ever the same then the method above will be very challenging. If your definition of "completely custom" means you have a system in place that allows you some customization within your system then the method above will be less challenging.



From the original questioner:
What I mean by optimizing is that when our engineer puts the 40 cabinets into a optimized list this would save sheetgoods, compared to only optimizing ten cabinets and having a lot of scrap.


From contributor K:
I think what the questioner is getting at is the fact that if he optimizes 40 cabinets all at once, the first sheets the sawyer cuts may have parts from cabinet #1 and Cabinet #40. This gets the best yield from the sheets but slows the assembly process until all the parts to all the cabinets are run through the other milling processes. By batching cabinets, the sheet yield might go down but could smooth the other operations because they are not waiting for parts for a particular cabinet to be ready to assemble.


From contributor S:
When optimizing, you shouldn't just be looking to optimize your sheetgoods, you should also be looking to optimize your time. When you ignore the time aspect of optimization the money you are saving by using less material could be used up in more processing time resulting in little or no savings at all.

Let's say you have to cut parts for cabinets at a shop cost of $120 per hour. Your plywood costs you $60 per sheet. By optimizing your cutting you use one less sheet of plywood which saves you $60. But, optimizing your cutting takes you 30 minutes longer to process all your parts and deliver a final product which ends up costing you $60. Your total saving is $0. In order to make an informed decision, you have to determine whether optimization saves you money or costs you money.



From contributor J:
This is an interesting question and one I've played with a bit myself. I'm sure we all have. I've read all the comments and have to point back to contributor J's statement. Only you know how your operation runs. Workflow, personnel, equipment, space, handling equipment, and etc. all have an impact on whether this will work better one way than another. I'd suggest you run jobs both ways, keep good records, and see which way works best.


From contributor R:
I would always favor working with optimized cutting patterns - higher piece quantities most often leads to higher yields. So batching a number of jobs will be more material efficient. A program such as our Itemizer software can list which pieces are for each cabinet. This would let you select which sheets to cut first. Cutting optimization takes little time and will provide the overview for informed material flow decisions.



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