Box lid sizing question

I’m making boxes where the top has a lip on the inside and I’m trying to figure out how much smaller the outer edge of the lip should be from the interior of the box. The boxes will range from 5 - 8 sides.

I plan to use small magnets to keep the lid on, but the lip needs to keep the lid aligned, not snug. I know I need to allow for swelling, but not sure what amount of gap there should be - what’s typical?

I made an 8-sided box before and made the lip smaller, but it wasn’t quite enough, so ended up doing a lot of sanding, test fitting, sanding, test fitting… until I got it right. I’d like to avoid as much of that as possible this time.

Thanks!

Can you measure the one you did already for the difference?
I’m guessing 0.005" - 0.010" per side for a “slip fit” with wood.

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That was where I started, but how much smaller I would make it would be a guess, because I’m not sure how much I took off in sanding - I wasn’t measuring, just sanding like a banshee with a ‘fine-ish’ grain (so I didn’t rapidly overdo it) and test fitting until it fit in all possible positions.

I’ll see how it goes with 0.010 per side. In this case if they end up with more than necessary gap it’s better than not enough.

Thanks!

If you are using magnets give yourself some room. The box with multiple sides can be a problem when sanding. If you sand too much one one face the lid will only fit on one way without giving you a gap at the top or bottom. So when sanding go lightly to avoid having to put the box lid on only one way.

If you are not using magnets a slip fit is best. You dont want the lid to just fall off when picking the box up.

Here is an older project to use as an example. I got a good press fit without being too hard to remove the box.

3x5_box_06082019.c2d (257.3 KB)

So when opening it will warn you about text and converting to curves. Just ignore and open and you can see my measurements. The left one is the bottom and the right is the top. The 3x5 box was designed to be cut from a single board. If you want to use this file be sure to save it again in V7 to get the tool paths. The file was originally created in v6 or below.

Here is an example of the 3x5 boxes. The top one is a completed box. The two below are the bottom in the middle and top of the box at the bottom of the picture.

Check out John Clark on youtube. He has several videos about box making.

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Excellent - thank you for the info, file and channel link (subscribed).

The sanding challenge I had previously was just as you described; the lid would fit a few ways, but not all. I did eventually get it to fit in each position, but not without a few ‘how am I going to get this apart without ruining it?’ moments. :grimacing:

Thank you

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