Getting the most out of a plywood sheet.

I would like to run this idea past everyone. I have a product I want to manufacture from 12mm birch plywood.

I can get 5 products from one sheet if I butt all the parts very close to each other and leave say 11mm clearance for the 10mm tool. There are 35 parts in total.

I am using a 8 by 4 sheet of plywood.

What I am thinking about doing is cutting a custom vacuum fixture which would sit under the whole 8 by 4 sheet to ensure the vacuum seal is not broken as the parts are cut out of the top sheet.

The plan is to use a 6mm sheet of mdf and cut the same toolpath but instead of using a 10mm tool instead use a 12mm tool and cut say 3mm into the sheet. I would then paint all the tool paths in the sacrificial sheet with a latex paint to seal the sheet only in the areas where it will be exposed.

I have never used a vacuum pump on my machine so this is something I would need to source and because the bed is so large the better the sealing I can get the less vacuum/ flow rate I will need. Also looking on youtube it seems vacuum hold down can be a little tricky to get to work right. I have heard of companies using two 25kw vacuum pumps together to get the hold down needed to hold smaller parts. I would like to avoid massive vacuum pumps at the expense of flexibility.

Hi Gav, I mostly use a 6mm cutter, and if worried about hold down just add a few tags. You most certainly do not need 2x25kw vac pumps, I only use 1 x 3.5kw vac pump, but a 7.5kw pump would be better. Some people rout out a holding sheet for repetitive work. That means routing out a groove slightly smaller than the component and putting a rubber gasket in that groove, that means that each workpiece will remain held in position by the vacuum, and the gasket is left undamaged by the cutter. That sacrificial board can then be saved and used for your next batch of the same items. I hope that mall makes sense. G.

That does make sense Geoffrey, the addition of a gasket was also something I was thinking about but was worried about the rubber/foam/cork getting damaged as I slide the sheets on and off the bed machine. I think a holding sheet will definitely reduce the need for a large pump and give me decent hold down.

Tabs are not an option as I plan to cut almost all the sheet material away so I am left with sawdust and parts :) Hence why I was thinking about painting the holding sheet as the surface area exposed will be quite large.

Make the gasket a nice tight fit in the groove, biggest corner radius you can and only have the gasket 0.3- 0.5mm above the square (say if using a 5mm gasket make the groove 5mm wide and 4.5-4.7mm deep] section groove, this will allow the top sheet to pull down virtually flat whilst cutting, and you should not damage the gasket when removing the sheet. G.

Where do you buy your gasket material?

I buy it on the roll (100M from memory & that lasts ages for me). I normally use 8mm as that suits my bed matrix, but it is available in various dias. Can't remember the company at the moment, but will check down the works and post tomorrow. A quick google search should show it anyway. I think it is called neoprene or butyl rubber. G.

If I remember correctly I think I get my gasket from a company called c.h.baines, they sell a rubber tube section by the metre and various diameters. I think I got some 6mm and 9mm last time, (it's all at work hence why I can't remember). The smaller diam works best as it's softer and you just cut the length you need for each groove