[_Rab_]

I'm new to CNC. I'm a hobbyist carpenter but I've recently become disabled. I'm therefore looking to CNC the components of a bespoke bookcase using a local CNC services provider using my CAD files.

I'm cool with the tooling; I can use Autodesk Inventor/AutoCAD no problem, so the DWF files are done, pending tweaks.

However having never done this before I wanted to ask people with experience using CNC about carpentry joints. The shelves rely on a stopped housing joint (a.k.a.. stopped dado, U.S./Canada). Now if doing these by hand, I'd use a jig and hand router and naturally end up with a slightly oversized housing/dado for my shelf (ie. a recess that is slightly wider than the thickness, slightly deeper than the width). If the first joint was too tight after a dry fitting, I'd adjust my jig/bit/technique and persist through the rest of the joints. My concern is that given the CNC will be far more accurate (and I don't really get a second chance), do I need to oversize the housing for the joint? i.e. If the shelf thickness is 18mm (approx 3/4") do I need to make the width of the housing slightly more than 18mm for it to fit and then take some PVA? If so, by how much? 0.1mm (approx 4/1000"), 0.5mm? I of course don't want to go too big, or the joint will lose its strength (and look amateurish). Is there an accepted practice?

NB. I have tried googling "oversize joints CNC" and things like that, but I really can't find anything on this.

Thanks
Rab

[ger21]

For the best fit, you'd need to do some trial and error testing.
From my experience, I would think that you'd need at least 0.2-0.4mm clearance, but it depends on a lot of factors.

[Gallen66]

That's a great question! I was wondering that myself. I found some answers online but i can't remember where. Most of the cnc joints are a bit altered. CNC Cut Wood Joinery: mkmra2.blogspot.com.