Author Topic: I need help with 1/2 blind dovetails in 12mm Baltic birch plywood  (Read 699 times)

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Offline android

  • Posts: 14
The lumber dealer where I live stocks 12mm and 18mm but not the 15mm Baltic birch plywood.

I have been experimenting with making drawer boxes out of the 12mm and putting them together with 1/2 blind dovetails using my Porter Cable dovetail jig. I'm using the 1" pitch sized 1/2 blind jig with the 17/32" 7 degree router bit.

 I've produced a pretty nice looking joint on the outside, BUT there is a small bit of the slot that shows on the inside of the joint. I think that is because 12mm is a bit less than the 1/2" that is expected.

Has anyone been successful using 1/2 blind dovetails on 12mm and if so, how did you get it set up?

Thanks for any help or suggestions.

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Offline android

  • Posts: 14
Re: I need help with 1/2 blind dovetails in 12mm Baltic birch plywood
« Reply #1 on: January 04, 2018, 07:32 PM »
OK, I actually did some measurements and some maths and some drawings and figured this out so I will share if anybody else ever wants to do it.

It IS possible to do this on the Porter Cable jig, but you cannot cut the tails and the sockets in a single pass as normal because the jig fingers have has to be move a bit between the sockets and the tails. Since you have to do this for most other types of dovetails, I don't think it's a huge inconvenience.

The correct tail length according to the 1/3 rule is 8mm. So, I measured the jig plate thickness as 6.6mm and added 8 to come up with a bit depth of 14.6mm. The bit stays at this depth for both cuts.

You set up like normal, but you move the fingers about 1mm forward so that the socket is not cut to a full 1/2" depth. Use the tail board to set up the cut, but remove it before routing. The sockets cut cleaning without tearing..

After you've cut all of the socket sides, you move the jig backwards just enough that the tail is fully cut in and rounded at the bottom of the slope. You need a sacrificial board on the top to prevent to tails from tearing out.

A tiny bit of adjusting on test boards may be needed, but it comes out nicely on the outside and inside corners. I'll get some pictures and put them up in the next day or so.

Offline charley1968

  • Posts: 491
Re: I need help with 1/2 blind dovetails in 12mm Baltic birch plywood
« Reply #2 on: January 05, 2018, 09:06 PM »
Thanx for the write-up,mate!
Just for today..

Offline android

  • Posts: 14
Re: I need help with 1/2 blind dovetails in 12mm Baltic birch plywood
« Reply #3 on: January 07, 2018, 05:00 PM »
Thanx for the write-up,mate!

You're welcome. I'm posting this here for safe keeping so when I lose my notes and have to figure it out again, I can look here!

Alright, here's the completed result and a few pictures to explain what's going on.

Half blind inside and outside corners. There's a tiny bit of tear out on my test box, but I'm getting an Amana router bit which is supposed to cut this plywood much more cleanly. But most important, no slot divots showing on the inside corners.

This recipe only works for 12mm Baltic plywood, but you can probably adjust it as needed for other thicknesses.

I used my small combination square to check the finger setback and make sure it was even.


This is the larger setback for for cutting the tails. I put the head of the combination square right between the 3-1/2mm and 4mm mark.  You need to use a sacrificial board on the top or it will tear, but you can use the same one for all of them and line it up straight behind since it won't be the real mating side anyway.

This is the smaller setback for cutting the slots. I set 1mm on my combination square for this one. Even though I was able to cut this without a sacrificial board, it helps to hold it all square, so I ended up using a common trash board for all of the slots.
« Last Edit: January 07, 2018, 05:07 PM by android »