Dovetails in plywood

[Dale Allen]

I decided to try some dovetail joints in baltic birch ply.
At this point I am not sure this is such a great idea. As you can see, there are still some voids in the layers and this came from Harville Lumber.
The ply measure .475" which of course is just shy of 1/2" by about 1/32"
I guess there is a reason the setup is for a minimum of 1/2".
The best I can do is leave small voids on the inside corner by not forcing the tails to seat.
If I cut the slots shallow, the bit does not allow me to do a climb cut prior to the finger cut and it just tears up the plywood surface.
Maybe I'm not thinking this through correctly but here's my solution, that I have yet to try.
I have some veneer that measures .038" thick.
First I put that behind the vertical piece in the PC4210 before clamping.
Then adjust the finger bar to make a slightly shallower cut, about half the .038" thickness. That way the climb cut will cut into the edge of the ply as needed and the offset of the veneer will make the tails that much shorter and should eliminate the voids on the inside.
Anyone else have any success using plywood that is not quite 1/2" thick?

 

[Dale Allen]

Well, for what it is worth, that solved the problem.
I had to do some additional minor adjusting but the setup is good now.
However, once this set of drawers is done, I won't be using plywood again.
Way too dusty and you need to go really slow to not rip off the veneer layers.

 

[Ted iin Michigan]

Dale - plywood is way okay for dovetails, just depends on the application. More of an aesthetic call than a materials one. I ALWAYS use half blind dovetails in plywood on my shop drawer projects and projects that I don't see as "higher end". Those would be things like basement or garage storage. I also used it in a kitchen project where the customer didn't want to spring for solid wood. And, yes, I've used 1/2" with no issues.

Maybe your jig won't work with less than 1/2". I use an older Rockler-style jig and it's not an issue. When the setup is right.

It's really important to have sharp bits when you do dovetails, and it's critical in plywood. Sounds like your technique is okay as you mention climb cutting the first, shallow pass.

You may have gotten a bum sheet of ply. I seldom (read almost never) get voids in Baltic Birch plywood. But it will chip out, esp if the bit isn't SHARP. That surface veneer is super thin and brittle.

 

[Dale Allen]

Ted, that seems to be the issue with this jig. It is set up for a minimum of 1/2" material thickness. I'm not able , yet, to get my head around the entire geometry of it at this time.
However, I would like to know some specifics of your older jig.
What bit and guide bushing does it use and is the finger spacing the same as the PC 4210?
I know the miniature setup for this jig uses a smaller bit and can use stock as thin as 1/4".

 

[Wingdoctor]

I used it for one project. It was sturdy enough, but the aesthetic's on mine looked like the brown smelly stuff. Yours looks OK.

 

[Ted iin Michigan]

Dale - most jigs use a 14 degree 1/2" bit with a 1/4" shank. If yours is the PC 4210 it is a little different than mine, but the way it cuts the dovetails is the same. Not in the shop right now but I will check the dimensions on the bushing and post here later. I saw a moderately decent video for the 4210 on YouTube here: https://m.youtube.com/watch?v=gwIdJyNzwxc . There are other videos, too.

Finger spacing is similar. My jig uses a replaceable phenolic template. And there are multiple templates that allow varied dovetail sizing so you can usually get a drawer size real close to what you want.

Like I said, you should be able to get good drawers in 1/2" ply stock. Keep playing with it. Pretty soon you'll be like me and you'll be replacing all the drawers in the house!

 

[Dale Allen]

Mine is the PC4210 and it came with a 17/32" 7 Deg Carbide-Tipped Router Bit, 1/2" shank.
I had done the 4 drawers on the first dresser and all those were solid wood sides.
After about 5 of the 1/2" plywood side, the bit cutting seemed to really slow down.
I removed the bit and noticed a lot of buildup from the plywood. I guess it is all the glue being cut. Had to sharped it 2 times to get through the rest of the drawers.

 

[Ted iin Michigan]

Okay - Interesting. Just a FYI, I did half blind dovetails today. Did 6 drawers in Baltic Birch plywood (fronts only) and had no chip out, buildup, voids, etc. You've mentioned voids, glue, etc with your BB. Wondering again if you might have gotten a bum sheet.

You may not need to resharpen so often. Most of the time just removing buildup will renew a bit pretty well.

I haven't done any research but maybe the geometry has something to do with the results you got in your second pic. The first pic doesn't look too bad except for the voids and some gapping at the base of the tails that seems to get worse as you look higher on the pic. Don't understand that. Perhaps a setup issue?

FYI - I have a different template that is for through dovetails and it uses a 7 degree bit (and a straight bit). Someday I'm gonna see if it will work on a half blind setup.

I'm thinking you may have picked my brain clean! Good luck.

 

[Dale Allen]

I may need to have a chat with the guys at the Hartville Lumber desk.
There are 3 sheets of 5 x 5 1/2" baltic birch that I am working with and there seems to be a lot of variation on the thickness as well. That has also had an effect on the dovetail cuts.
While I would have thought they would carry quality stuff, maybe not so much.
Where else do I buy it?
Also, when I said I sharpened the blade, it was basically just scraping off the buildup. However the first time I did run it across my DMT stone a bit and it helped some.
But that bit is not what I'd call a quality bit because the flat of the carbide has a very rough grind, like harbor freight lathe ways!:biggrin:

 

[Ted iin Michigan]

Dale - There's Baltic birch and then there's REAL Baltic Birch plywood. I've used some lookalike birch plywood in the past that wasn't particularly good. I'm not a China basher but I believe that's where this stuff was made. Lots of plys but they varied in thickness and there were voids, glue pockets, etc. It was okay for what I used it for but it just didn't measure up to the real thing. They called it "furniture grade". Right

I'm not familiar with Hartville Lumber but I know Woodcraft carries BB as well as Rockler.

 

[Gary Beasley]

You may need to figure a good place to put a sacrificial piece of wood in to prevent the tearout, either clamped up side by side or butted to the edge.

 

[Dale Allen]

Did some additional checking before I had the talk with the lumber guys.
Seems some of the pieces are 7 ply and some are 9 ply.
That will definitely be discussed.
The stuff that is 9 ply measures out at around .498"
The other stuff is anywhere from .460 to .487
They do advertise it as baltic birch 9-ply 12mm, which is .472", but then the 12mm may be a 'nominal' measurement.
I'd sure like to get ahold of the guy who thought that up!

 

[jttheclockman]

As Ted said there is different Baltic Birch plywood grades. There is also different quality grades with Aircraft grade the very best. There is BB being sold under the name Eurobirch which is a lesser grade. Most BB is coming from China and quality control is not something they are known for.

True BB comes as 3mm~1/8" 3 ply
6mm~1/4" 5 ply
9mm~3/8" 7 ply
12mm~1/2" 9 ply
18mm~3/4" 13 ply

Anything less is not true BB.

Buying lumber is not easy these days. Even furniture grade maple or oak plywood has voids. The days of buying a true 2 X 4 are over and continue to shrink.

Buy the way Finnish plywood is nice to work with also.