Thinking through fit & tolerances

Hello! You all were so helpful last time I figured I'd give this question a shot here since I cannot seem to find accessible internet resources...

I'm designing custom furniture from plywood on my ShopBot and I'm experimenting with different tolerances so I can get the "just right" fit. I need some help thinking through my designs from paper sketch, to 3D model (I'm using SketchUp) to vector image upon which I can lay my tool paths.

I'm comfortable creating designs that fit, albeit with not enough tolerance.

Does it make sense to build the tolerance into the 3D model, or is there a way to adjust his within VCarve?

I'm really just hoping to learn about various workflows so I don't have to just go trial and error.

Thanks in advance for the help!

Matt

Matthew, You can adjust tolerance in VCarve Pro easily enough. When you cut your pockets, there is a "pocket allowance" in the toolpath selection. TJ usually uses ply and I believe uses .01-.02" usually, Unless the piece is designed for a slip fit to be taken apart regularly. Use calipers for thickness of ACTUAL wood every time. Maybe cut tenons first so you can test check fit before removing your mortices from the machine, as it's easy to go a "smidge " more if you need to while it still fastened down. Once it's off--all bets are off.

I'd add to what Scott said that the thickness will vary across the sheet. Occasionally, the variance can be quite large - greater than 0.05". The thickness will vary sheet to sheet and lot to lot.

I use a lot of Baltic birch because the variation tends to be less than other plywoods; however, even Baltic birch is getting worse with time.

Paul Z