Dovetails and thin plywood

[GLFaria]

I want to make some assemblies with dovetails in 5mm ply.

I have been using x-actos with new blades and very sharp chisels. This is proving to be a pain in the back, as no matter how careful I am there is always some bit or other of the plywood that breaks apart, specially at the tips and, of course, at the outermost ply, where it will show.

Is there any special technique that can be used, or is this just one of those things you don't do?

Thanks

 

[custard]

Plywood and dovetails just don't mix...for exactly this reason!

If you absolutely have to use plywood then you could try backing it up with a sacrificial piece of wood to support the ply and limit the amount of breakout, it will help but probably not solve the problem completely.

 

[AndyT]

Ikea manage to make little boxes and magazine files from even thinner plywood, with box joints rather than dovetails. I would think they would be made by clamping up lots of layers together before routing the slots, so giving the sort of support custard describes. It's pretty good quality birch ply without internal voids.

 

[GLFaria]

Ikea manage to make little boxes and magazine files from even thinner plywood, with box joints rather than dovetails. I would think they would be made by clamping up lots of layers together before routing the slots, so giving the sort of support custard describes. It's pretty good quality birch ply without internal voids.

Yes, I know those boxes.

What I am making - drawer partitions for cutlery and silverware, for my home - does not indeed require that the dovetails be perfect, as they will be nearly invisible in the end. It's just that I feel I should do better.

No router or any other power equipment, though. I cut the PW to length, 70mm wide strips, with a purpose-made jig, a bit like a cutting-gauge. Turned out pretty well, especially after I planed the pieces to final size.
I'm working with a very soft white pine, low quality plywood - that's the only material I manage to get in sizes small enough that I can store it at home...
I am marking only the faces of the pieces with a cutting gauge - not too deep, lest the outer ply separate. I found out that by gripping a number of the pieces together in the vise and sawing the tails with a small hacksaw (one those smallish hobby saws with 6" blades, about 1mm kerf or less) with a thin blade I manage to cut the tails at least adequately. Then I cut the excess "wood" with a hollow-ground chisel to reduce the pressure on the ply (I first tried it with a bevel-ground chisel, no good for this thin, fragile material).

Tomorrow I'll deal with the remaining tails and the pins. 17 pieces in all to make.

Of course, the fact it's my first try at dovetailing does not help, what with the quality and thickness (or rather thinness) of this PW...

 

[Jacob]

Sounds difficult/impossible.
If you must do DTs perhaps just do one per corner i.e. on a 70mm piece have a tail (or a pin) about 40mm wide.
Mark only with a pencil to avoid cutting through the veneer.
Sawing a stack together is difficult and not traditional, but with ply might be helpful as you might get less break out.

 

[bugbear]

Of course, the fact it's my first try at dovetailing does not help, what with the quality and thickness (or rather thinness) of this PW...

That does sound ... ambitious!

BugBear

 

[Racers]

I would do tongue and grove joints for the corners. Its what I did for my knife and fork rack thing.

Pete

 

[GLFaria]

Of course, the fact it's my first try at dovetailing does not help, what with the quality and thickness (or rather thinness) of this PW...

That does sound ... ambitious!

BugBear

:lol: :lol: :lol: Yes, I'm finding so!!!

 

[AES]

A trick from my aeromdelling days which MAY help - try soaking the ends (faces and surfaces) with thin cyano acrylate ("super glue") and allow to rdy (30 mins to be safe). That should help stop little pieces breaking off as you cut. You could also try cutting with a fret/piercing saw using the blades from jeweller's piercing saws - like a normal fret saw but MUCH finer.

HTH
AES

 

[GLFaria]

Well, as might be expected (except by me, that is ... ) the exercised proved futile.

In fact, I only wanted dovetais for reinforcing the outer corners, not as things of beauty, in the end they would be invisible anyway. The problems originated not so much on the "notches" I made that could have passed for dovetails, but on the frailty of that 5mm PW.

After cutting dadoes to 1/2 thickness depth on the outside "walls" for assembling the inside partitions- which meant leaving a 2.5mm "thick" wall at the bottom of the dado, when I started to test assemble everything started breaking at the dadoes. As well they should...

So, back to square one, I'll use thicker (although not better quality, I'm afraid...) PW, and will no longer waste my time and patience trying to make dovetails into plywood - this time it will be lap joints.

Always learning... maybe in 20 years time...

 

[Benchwayze]

I have made drawers with plywood, using box-joints, cut on a wobble-saw. (at the time that was all I had). They were successful, with a backing piece to help avoid spelching.

For making cutlery divider boxes, I might not even go as far as box joints, using butt-mitres instead.
You can strengthen these joints with model-railway 'track-pins' which are sharper than a tack, and so fine they are virtually invisible against a dark wood.

HTH

 

[Phil Pascoe]

I used to find "chemically blackened gimp pins" from an apiarist's suppliers useful. They are about 20mm. thin, but with a head like a wire nail. If you have a friend who keeps bees, they're worth a scrounge.

 

[rafezetter]

A trick from my aeromdelling days which MAY help - try soaking the ends (faces and surfaces) with thin cyano acrylate ("super glue") and allow to dry (30 mins to be safe). That should help stop little pieces breaking off as you cut. You could also try cutting with a fret/piercing saw using the blades from jeweller's piercing saws - like a normal fret saw but MUCH finer.

HTH
AES

+1 and what I was going to suggest. plus have you tried cutting with something like a gentlemans saw which can have very fine teeth.

I picked up something akin to them in a modelling place designed to cut thin plastic for just a few pounds with a very thin kerf and leaves a good finish.