Birch ply cab

Chalky

I'm quite happy with making a finger jointed pine cab so wondered what are
A) the benefit of an 18mm birch ply cab over an 18mm pine cab
the best joints to use on a birch ply cab
C) the pros and cons of covering a birch ply cab or is it no different to rounding off the edges of a pine cab and sticking on the covering?

Wisdom please from the experienced cab builders!

paulnb57

Surprised there are no replies, I have no experience with using Birch Ply as you suggest, but my gut feeling would be to treat it the same as anything else, I would finger joint it if I had (and I sooo wish I had!) the ability. I would also round the corners the same a "normal" timber and cover as usual.... I guess that ply would be more stable than pine, less likely to split, but would have different tonal properties......but be stronger........

ICBM

I've only ever built a hardwood cab, so I can't comment on the jointing. I used mitre joints with internal battens so it looked neat.

On the tone properties, ply sounds tighter and punchier than pine, all else being equal. Pine is 'sweeter' but can have more odd overtones. Ply is still more resonant and vibrant than particle-board or MDF though.

Generally I would avoid pine if you're going for heavier distortion sounds, although it can sound very nice for cleans and light overdrive.

Don't try to make the baffle from pine whichever you choose, always ply.

hywelg

Birch ply is stable pine not so much. Difficult to find really good 'unsorted red deal' in widths suitable for cabs, at least round our way.

Because the grain goes in different directions a dovetailed Birch ply joint won't need any battens. A fingerjointed cab should be OK, but relies heavily on the glue, whereas the dovetail is a mechanical lock. I had a Fender cab go loose on me, finger joint glue didn't hold.

Yes always round over the outer edges, at least a 12mm radius it makes covering easier and when it gets a knock it's less likely to get damaged.

Chalky

I thought I might get breakout when cutting dovetails on plywood? Maybe only if its cheap - I guess marine ply would be best?

jpfamps

You can do dovetails with ply, but finger joints are recommended.

With dovetails you can have issues with delamination of the ply in joints.

You should use void-free birch ply.

Marine ply is designed to be moisture resistant, not really a requirement for a guitar cab.

Popular ply is another option: it's much lighter than Birch ply, but is a softer.

18 mm is excessive for most applications, especially if you are using jointed corners.

Most manufacturers don't use 18 mm ply for the sound, but to save time (and hence money) during construction as the corners can be butt jointed and stapled easily (18mm is a bigger target for the staple).

It's cheaper to make cabinets using 18mm ply like this than using slightly cheaper 15 mm or even 12 mm ply with jointed corners.

hywelg

Never had problems routing Birch ply dovetails. Just need to make two passes.

Ordinary ply is going to cause you problems, the laminations are too thick 18mm ply is 11plies IIRC.

Chalky

I thought marine ply was voidless as well? Think I'll go with 18mm finger jointed then. Many thanks all!

hywelg

I took some photos when I was putting together the last two 2x12 cabs. You can see that dovetailed birch makes a very neat joint. Its very easy to work with, it doesnt chip or catch when routing.

http://www.ladybayartglass.co.uk/Private/HywelHarris-StuffForSale/StuffForSale.htm?ssm=89

Chalky

I see what you mean. Half blind dovetails and is that 18mm and did I count 13 ply?

matt1973

Imteresting thread. In my experience, pine seems to route easier on box joints. And if you are indeed routing the joints, it's advisable to use some thin scrap to back up the main piece so as to minimise tear out. 

A good router bit is also essential for cabinetry so forget the high street DIY shops - Axminsters own are pretty decent for the money and its only £1 delivery.

And definately do not buy crappy WGS, Spruce or whatever God awful ply you'll see in 99% of wood yards. Although you seem to have already figured that out

@jpfamps I've always fancied having a go with Poplar Ply. Where do you get it? I can't find it anywhere.

matt1973

I might also add that I genuinely feel a rebate join is good enough for a guitar cab. Although, unlike a box joint it isn't self-clamping so additional tooling is required. But much less of a headache if you're new to cabinet-making.

hywelg

Chalky said:

I see what you mean. Half blind dovetails and is that 18mm and did I count 13 ply?

Yes 18mm, and yes I think it is 13. Its what B&Q stock and the only reason I use it over 15mm ply is that they will do a good job of cutting it into 300mm planks ready for chopping into cab pieces. They dont stock 15mm.

Dont underestimate how difficult it is to get a good, square cut on 8foot of heavy timber. Even with my Makita table saw it needs 2 people and great care, and even then the blade isn't exactly 90° to the table.

I have one of these.

http://www.axminster.co.uk/axcaliber-dovetail-jig?gclid=Cj0KEQjwsb-vBRCLj7TvqpGx_MoBEiQALgFGnuFdLsN1EHtB5NZRQ-tP1RZmgoiVgB2ggPaMiMA0wzQaAuE_8P8HAQ

But when I bought mine it was £35!. I can get it to take 300m wide timber by removing the left hand stops. I have a beast of a router (2.3kW) and it makes short work of it. It will also do finger joints but tbh, why would you not do dovetails with this? Needs a bit of setting up each time. I run up a couple of pieces of scrap to check cutter depth and jig setup.

Chalky

Ok @hywelg, thanks to you I bought a secondhand Trend DJ300. I had ordinary 18mm ply, not birch, so I tried that. Already had a cheap Screwfix router and cheap bit from a Screwfix set but the results weren't too bad. But the dust! Can't fit the router dust extracter with the bit set so low. Out of the 4 joints I did 2 not good and 2 adequate so strengthened with cleats.

Going to try it on 18mm pine next to see it I can get better fit - will make one with dovetails and one with dowels to compare and contrast. Thanks for the steer!

hywelg

The thing is with these Dovetail jigs is setting them up. You'll need loads of offcuts, with good square ends to run some test joints. I have a screw adjust depth gauge on my router , that helps a lot. The two settings that need very careful adjustment are the stop on the jig and the depth of the cutter bit. I think there are a few videos on YT about how to set them up, spend some time to get to understand which adjusts which.

Then take two or three passes with the router before going to full depth in the guide slot, it helps to prevent breakout. Make sure the cutter you have is really sharp, they are cheap enough to buy.

Then when glueing up soak the joints (ideally with a diluted glue) before applying glue otherwise the glue starts to thicken due to absorption of moisture by the wood before you get chance to knock it all together. I use a wooden mallet to bang them together. Finally check that its all square before allowing to dry. If not apply some compression diagonally to square it up. I use sash cramps but you really wont need much force so you could improvise with some stout string and a piece of stick to wind some tension on.