Kerf and finger joint size

I’ve been working on a couple of different boxes with different finger joint sizes and I’m finding that the smaller finger joint is giving me a really tight fit and doesn’t need glue, but the larger finger joint is not as tight and I have to use glue to secure them. The smaller joint size is at 0.25in and the larger one is at 0.375in (both without kerf). I’ve determined that my kerf is 0.008in, but when I apply that to these two different finger joint sizes I don’t get the same results. Is this weird to have happen?

What material is it?

I’ve printed these boxes on a few different materials - basswood and maple plywood, and here recently on Baltic birch plywood. This issue is only happening with the larger finger joint, the smaller finger joint has been consistently tight no matter what plywood I was using.

How are you adjusting for kerf in your design? If it’s happening on the exact same wood with the only difference being finger size, the only thing that makes sense is that somehow when you adjusted your design for kerf some kind of error snuck in.

This is how I approach these builds each time. It’s a longer process I’m sure than other programs, but it works for me - I don’t mind the time. :slight_smile:

When I get my box size determined and drawn out in Illustrator I then add in the finger joints. When I’m sure I’ve got the joints in the right spot I then adjust for kerf on each finger joint individually by 0.008in.

I’ve only got the one file where I’ve used the larger finger joints. I think I’ve rebuilt it 5 times now during my learning process, looks like the 6th time might be the charm.

So I completely deleted the original AI file and rebuilt it again. The sides fit tight into the base, but it looks like I’ve got an issue with how I’ve laid out the joints on the sides because they aren’t tight at all.

Sigh… back to the drawing board.