Compiling General Build Knowledge

[cforger]

Hey all,

I'm getting ready to build my first BFD cabs (Tuba, DR250) and I've been sifting through the forums trying to learn as much as I need to know. I've got a few pointers here that I'd like to get confirmation on, maybe have someone expand on them a bit.

If people wish, I'd happily refine all this into a mini-faq that can be posted as a sticky later on, I'm sure other people would appreciate finding the knowledge in one place.

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Since it’s hard to find proper Baltic Birch all over the world, here are some considerations you must put in mind for selecting proper wood.

- Baltic Birch is selected as a premium plywood because it’s generally free of voids (holes in the ply layers) and is constructed of more plys than the average 3 or 4 ply construction wood. This results in more stiffness and strength, but also more weight.

- ½ “ Plywood should have at least 5 plys in it (http://billfitzmaurice.com/phpBB2/viewt ... tuba+birch) Make sure there is NOT a thin veneer on one or both of the outside edges. The thin finish veneer will be bonded to the PL glue, and it will shear off from the plywood under stress.

- Question ) I thought I saw a thread that stated that regular ½ ply works for the Tuba24, and you don’t need BB. ??

- Home Depot in Canada is carrying “Russian Birch” which seems to be the same as Baltic Birch. Look for 2x4 and 4x4 sheets of it in the “Handy Board” section.


- You can use ¼” Plywood for the bracings if you dado slots for them. If you don’t, you’ll have to use the recommended sizes. Q) Can you use any generic ply, like 3 ply fir for this? Could you use hardwood for the braces to further save on weight and make the last braces look nicer, or would resonance issues be caused? How deep should you dado? Say 1/8 “or 1/16”?

-You don’t need to drill holes in the bracing, other than the first set of bracing closest to the driver. Q) Does this apply to all models? Is there any advantage to having holes in the other bracings?

-PL Premium expands 3:1, and can be suitable for making sure you have air-tight joints. If you need to caulk, there is some debate about the use of Silicone. Bill believes to stay safe and not use it, other builders claim to have been using it for 20+ years with no ill affect to the drivers.

-PL Can be cleaned up with mineral solvents or WD-40 when still wet. When it’s dry, you’re going to have to abrade it off your hands or other surfaces.


That's about the jist of what I have at the moment.. confirmations and more info welcome. Like I said, I'll record it all, distill it, and repost once I have something concise.

[Sydney]

I built my T24 with 5 ply plywood handi-panels. I have seen earlier T24s made from plywood that was definitely NOT Baltic Birch.
That said, the advantages of using it, are a denser more consistent wood product, without voids, and probably less likely to chip at the edges.
Built carefully, little or no additional caulking should be necessary.
( Dried PL will come off your hands after washing dishes once or twice )
As far as silicone is concerned: I hereby officially suggest you play it safe, UNLESS your are sure it is a safe formulation - ideally with no corrosion warnings.

[AntonZ]

Thanks for starting that list, can be useful if you keep adding to it.

-You don’t need to drill holes in the bracing, other than the first set of bracing closest to the driver. Q) Does this apply to all models? Is there any advantage to having holes in the other bracings?

Holes in the braces save weight. They need not be airtight, only make the panels stiff and they do that with or without holes. Making the holes can be a bit time consuming but you drill once and lift often, so I'm all for weight saving.

[cforger]

AntonZ wrote:

Holes in the braces save weight. They need not be airtight, only make the panels stiff and they do that with or without holes. Making the holes can be a bit time consuming but you drill once and lift often, so I'm all for weight saving.

Well, I'm thinking the weight savings of drilling holes in a 1/4 inch plywood would be negligible. I saw one post from Bill stating that holes in the braces were only sonic necessity in the first set, to allow the waves to mix. Since he used the word "Necessity" I'm not sure if that means there is still sonic advantage to having other braces drilled out or not..

So to extrapolate on the weight savings: If you're using 1/4 poplar or similar hardwood instead of ply for bracing, it's lighter than 1/4 ply, and it looks nicer for finish reasons - The only question is if the resonance of solid wood would cause any problems here in Tuba design? I know you can't build a cab out of solid wood without colouring the sound.

And I will compile all this together - I'm about to build, and I'm trying to extract as much gold from this forum before I buy all my parts. I figure after I build one, I'll want more, so I may as well get it right the first time.

As for weight savings, using some regular 4 ply fir / pine ply would really save more on weight - I'm figuring if it's used for the internals, and the externals are 1/2 BB 5+ ply then things should be okay? If people are building entire boxes out of the regular ply, this must be a better method, yet still give a good finish for the outside, and extra durability. The inside throat is 1 sheet of plywood almost, so that's a fair savings in weight - 5-10 pounds I'd say over a sheet of BB.

Comments?

[Bill Fitzmaurice]

using some regular 4 ply fir / pine ply
Comments?

I would not use four ply 1/2", and say so in the plans.

[cforger]

using some regular 4 ply fir / pine ply
Comments?

I would not use four ply 1/2", and say so in the plans.

Ah, busted - for want of a ply.