Plywood and its inconsistent thickness

[Gene Davis]

I am about to go out with a 25 sheet job, and am getting different stories from production share shops. One says the premium way to go is the way they do all their in house jobs, and use plywood. The other says the material sources he has for stock don't have the good material they used to stock, and the thickness variation not just sheet to sheet but within sheets makes for risky fits.

My joinery is all lock dado, and used to be blind dado. But lock dado is really just blind dado interrupted by fastener breaks, and the fit issue is really the same one versus the other. Or is it?

I set my fit to .010 with .030 depth, exactly per what I got in sample seeds from shop number one. What can I expect>

[Donald Thomson]

One of things that eCabs does to accommodate this varying thickness is to zero the bit to the table surface and not the surface of the material. I cut several hundred sheets of plywood per year, on my ShopBot machine (2009) using ShopBotLink, and the zero to table has made it so all my joinery works well. The only place I've had to make adjustments is when cutting Appleply (Baltic Birch) for drawer box parts. This is a MUCH harder material then regular ply, so I've had to increase spindle RPM and slow down feed speed to accommodate for bit and machine flex.

You'll find that spindle RPM and feed rate will account for a lot in nice fitting joinery. When I was obsessed with cutting speed (fast) I had really sloppy fitting joinery. Since slowing feed and increasing RPM joinery fit has been excellent. You'll need to experiment with your machine to determine what those feeds and speeds need to be. Your mileage may vary.....