Do tight wood joints need a gap?

My prior CNC experience is with a 3d printer, where I learned that fitting mated pieces means oversizing or undersizing one end. e.g. a 10mm peg into a 10.2mm hole.

In general, is this something that I need to worry about when designing wood projects for the X-Carve? What about when considering glue joints vs press fit joints?

You might need to iterate your design a little to get it working just right.

Typically I design without a gap; I can always sand it down.

One thing you also have to watch is your bit diameter. Your CAM program may believe your bit to cut .25 inches wide but in reality this might be .248. This then makes your slots narrower and your tongues wider and holes will be smaller than designed.

You just have to run your design, find out how it fits and make adjustments to your design.

No one goes the CNC route to make one of something, They choose the CNC route to reliably make consistent products.

The same rules tend to apply with subtractive CNC as with additive in regards to fitting pieces, with one additional factor of finish treatment.

wood parts are usually expected to receive light sanding, metal and plastic parts may receive deburring, and any part may receive surface treatments like paint/wax/etc.

with wood especially, as Harry said, sanding is not just the preference, it’s pretty much expected anyways. In fact if you are wanting a friction fit, you might want to oversize your tabs a hair and sand down. if you’re seeking a glue fit go with exact dimensions and sand down if it requires more than hand pressure to join without glue, and only for a loose fit include gapping.

Great, good to know, thank you!

Just remember that circular bits can’t make sharp square inside corners so you either have to plan for that in the design (dog bone joint or such) or just chisel it after the fact.

You also need to consider that wood is a material that shrinks and swells with the humidity inside. Heat on…wood gets narrower and shorter a bit. Humidity levels increase…wood expands in all directions. I wouldn’t leave a gap.

Yes, agreed on the humidity. I’ll try and keep that in mind as well. And thank you Justin for the reminder. My plan uses curved mortises on all of the parts I can get to from a single side, and was going to use a combination of chisel and a square file for the rest.