Mitre key questions

**labr@** · 14th November 2021, 09:43 PM

I've just finished a small box in blackwood and silky oak and am reasonably happy with it but the mitre keys are not great.

With some of them there are small gaps between the end of the key and the end of the slot. I tapped them in place quite firmly and thought they were all well seated but the gaps appeared after trimming and smoothing. Of course larger gaps can be filled and very small ones fill with the finish but they are still visible so are less than ideal.

I prefer the appearance of thinner keys and would like to go down to 1.6mm (or possibly less) from the current 2mm but I expect that these would be even harder to seat fully without breaking them.

Also, I use a slot cutter in a router to cut the slots and had a small amount of tearout on the exit side of a couple of the slots despite using masking tape all round.

Does anyone have any tips on mitre key installation that might help to prevent these issues in future?

Thanks in advance for any advice.

P1110625 Reduced.jpg

**KeithP** · 14th November 2021, 10:08 PM

I hand cut the slot and use a piece of veneer for the key.
This is quite strong, be sure the grain of the key is running in the right direction.

Regards
Keith

**Treecycle** · 14th November 2021, 10:17 PM

I have had that problem before where I thought the keys were seated correctly only to find the dried glue in the bottom of the slot when cleaned up. I put it down to trying to make the keys too tight in the slots and they grab because of the glue swelling the timber before they get pushed all the way in. Maybe I was wrong in that conclusion but I make they an easy sliding fit now and don't seem to have the problem. I just make sure I hold them in place until the glue has got a grip.
I made a jig to hold the box at 45° and the cutter cuts through the jig as well as the box so that it gets support behind the exit side of the cut. The jig just slides along the fence. I would take a photo for you but it's pouring rain here at the moment.

**labr@** · 14th November 2021, 10:42 PM

Thanks Dallas. I think you've hit on the cause - or at least part of it. I made the keys a tight fit to be sure there would be no gaps. Sounds like I can back off to a looser fit with no fear of that. It will also enable use of thinner keys.

I know what you mean about the 45 degree jig - that's what I use too. Must have a close look at it to see why it is not supporting the exit area.

**RGP** · 17th November 2021, 06:16 AM

I found cutting the key to a tight thickness, gluing the slot then hammering the key with a flat faced hammer just before you insert it makes a good tight fit as the wood swells very quickly. Check out some Japanese video's on You tube. The other trick is to curve the inner face of the key as the slot cutter may not be cutting a flat slot. Cheers RGP.

**mpot** · 17th November 2021, 12:17 PM

Originally Posted by RGP

The other trick is to curve the inner face of the key as the slot cutter may not be cutting a flat slot.

Yep - that's my approach too, as I find it definitely helps.

Here's a quick'n'dirty diagram to show this - with the concave shape emphasized for clarity:
spline.png

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