What size hole should I draw for 18mm plywood?

New user - Last week my machine was very inaccurate after recently being assembled, thanks for the talkshopbot support. The problem was that the pinions were not tight and then when tightened they loosened again and needed threadlock and had to be tightened again. (Should be added to assembly manual.)

I'm not sure the machine is accurate still. Making two drill holes 18mm/50mm/2000mm apart all seem to be very accurate, but profiling or pocketing a box 18mm x 50mm does not fit a 50mm x 50mm x 18mm part into it. Tried drawing the rectangle at 18.4mm and still too tight where the cut is just below 17.9mm. I need to draw it as 18.8mm x 50.8mm to fit it. Is this normal or is something still wrong? Any ideas?

Gary Campbell wrote this nice little file to check your machine for square an distance settings.

mic bit diam and material...i always oversize pockets and holes .25mm for slot furniture

Jerry: Are there any more details about this file?

GC3: Good to know! I presume if you draw 18.25mm you get 18.25mm though...

GC3: Good to know! I presume if you draw 18.25mm you get 18.25mm though...


exactly!...ck your uv settings these cut on the pr...clean and crisp :D

Change your machine to inches and run it I didn't realize where you are from. Once you get it to cut the correct dimensions you can change it back.

James, I seem to remember your .25" bit was in database as EXACTLY .25", are you absolutely SURE the tip measures that? Sorry to sound like a broken record, but not a single one of my 1/4" bits measure .250". Also check material several different places like Gene says. TJ normally has 3-4 different versions of his ply files and the only thing different is ply thickness. Glad things are better, but the only thing you should be having to change is your pocket allowance depending on the type of fit you want.

Allowances always have to be made when cutting male and female parts. A lot depends on bit deflection, climb/conventional cutting, material, speed of cut etc etc.