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My solera (workboard for classical guitars) made of two sheets of ordinary plywood laminated together has warped, so I need to make a new one. What sheet stock is most stable in the long run - Baltic Birch ply, MDF, or something else? I'd prefer to use the baltic birch, since I will be machining it quite a bit to accept bolts and such.

Secondly, for whichever stock you recommend, is laminating 2 sheets together necessary to minimize warping? I'd prefer not to, both to save costs and to reduce weight.

I used 3/4" birch ply (dunno if it was Baltic or not) for my solera. I built mine over two years ago and it is still flat. One thing I did do, though, was I sealed it with tung oil. Perhaps this has helped some.

I also use 3/4" birch ply as backing plates for my MDF radius dishes. MDF warps easily, so using a good plywood for backing material is necessary, I've found. I also sealed these pieces with tung oil and even applied tung oil to the radiused surfaces of my dishes. They drank it up like sponges, but I figured it couldn't hurt.

Tung oil, Watco's Danish Oil Stain, or anything similar should work as a sealer, I would think.

Best,

Michael

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Live to Play, Play to Live

Real Baltic birch is great stuff. The fake stuff isn't anywhere near as good. Most of the fake stuff is made in the USA. Real Russian or Baltic Birch is the best. My experience has been similar to Michael's with it.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
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In general, if you use more than one sheet of something, you want the overall laminate to be symmetrical. In the world of composites, which I used to inhabit, you want what is called a "pseudo-isotropic" layup)

For example, if you laminate two sheets of plywood, you should have the grain (of the outer plies) in the same direction. If the outer grains are oriented at right angles, it will tend to warp into a saddle shape with changing moisture content.

Never use two different materials-like MDF and plywood, or even two different kinds of plywood - together (with one sheet of each) because they will change size differently with time and moisture change, and that will cause warping or dishing.

You can use different materials is you keep it symmetric. (example, plywood-MDF-plywood, with the plywood outer grain in the same direction)



In my experience, baltic birch plywood seems to be the most stable - not because birch is more stable than fir or pine, but because if generally has more plies.

Baltic birch with plastic laminate on both sides seems to be particularly stable (and, very stiff for the overall thickness and weight.)


If you use sealer, make sure to use it on ALL surfaces (front and back)

Phil

Thanks, looks like baltic birch is the way to go.

I did seal my last solera, albeit with shellac. I have plenty of tung oil around, though, so I'll probably use that this time around.

Thanks for the advice, everyone.

Roger

[QUOTE=Phil Marino]
Never use two different materials-like MDF and plywood, or even two different kinds of plywood - together (with one sheet of each) because they will change size differently with time and moisture change, and that will cause warping or dishing.[/QUOTE]

Well, that certainly makes sense. It is my experience, however, that MDF will warp if I just look at it too hard, so a backing material is necessary for something made from MDF that needs to retain its original shape, be it a solera or a radius dish.

The radius dishes I have, I bought a couple of years ago, attaching them to the birch ply pieces shortly after I received them. They are still dead flat. Granted, I keep them in my shop, where I'm conscientious about humidity control, so perhaps this is why I haven't experienced any warping. But I have one dish that I bought and let sit around for a few months in my shop before attaching it to a piece of ply backing, and it was no longer flat (it had beeen leaning up against the side of a workbench, which probably accounts for this). I had to flatten it to the plywood by using drywall screws. So far, no worries on that one either. But I'll keep a weather eye out.

So, I need to ask, Phil, what sort of backing material would you prefer to use for an MDF radius dish or solera?

Best,

Michael

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Live to Play, Play to Live

[QUOTE=Michael McBroom] [QUOTE=Phil Marino]


So, I need to ask, Phil, what sort of backing material would you prefer to use for an MDF radius dish or solera?

Best,

Michael
[/QUOTE]

Good question - I have very rarely used MDF - I just don't like the stuff.

To answer your question, the only thing I would glue a piece of MDF to is another piece of MDF (as close to the same stuff as possible) to avoid warping with time and moisture change. . Since MDF seems to be so unstable when used for radius dishes, I wonder why people use it.

I just made my first radius dish from a laminate of two pieces of 3/4 birch veneer ( poplar core) plywood. This is the stuff you can get at the BORG for about $45 a sheet.

I selected a relatively flat sheet to start with, and glued the two pieces together clamped on top of my workbench (very flat) so the sandwich came out quite flat. It's about 1 1/2 inch thick but still not too heavy, and will likely stay very flat. And, it was easier on the router bit, and didn't create as much nasty dust, as MDF would have. Is there some reason more people don't do this?

Phil

Good points and good questions, Phil.

This is probably stating the obvious, but one of the keys to keeping sheet goods, esp MDF, flat is storing them flat on a shelf -- NOT leaning against a wall or something. MDF, in particular, will warp because of its own weight if leaning. This is one of the reasons I rarely buy and almost never store whole sheets -- don't have room for them. But I have a storage sytem for pieces up to 36" x 80" stacked flat on top of each other -- it can be a fun puzzle to arrange pieces to keep them all flat.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

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if you are seriously wanting premium sheet goods then you can't go past die board. hard to get around its price though.

Die board?

I've never had any MDF sheets warp, twist, nothing. I just buy them, and cut them up immediately. No point in storing larger pieces/sheets of the stuff; it's bulky, the price doesn't go anywhere, and it's readily available. My radius dishes are doubled up, and finished (because I broke through the hardened surface, natch), but they haven't budged at all. All my bending forms and building forms are made of MDF (Baltic Birch would be nice, but honestly, for the massive upcharge, I don't see the advantages), none of them move. I tend to make good quality ply master templates, and MDF working templates and the like.

And yes, the dust is nasty, but the material's really not that bad to work with. For non-stress situations (which radius dishes, molds, bending forms qualify for, IMO), it's an excellent, highly affordable option.

I will point out that the solera is used to set the neck angle on classicals, so straight is really important. A 1mm shift over a yard is pretty signficant in terms of what that does to the action.

I'm not a huge fan of MDF, but in keeping with Phils' comments about quasi-isotropic laminates, MDF is probably the most isotropic material any of us have in our shops.
I have some 1-1/2 thick dishes that I've used for many years that have stayed true.
But, I really keep thinking I should make some out of BB plywood some time, mostly because I don't like MDF it just seems cheap somehow.

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Jim Watts
http://jameswattsguitars.com

die board is an extremely strong, dimensionally stable maple plywood used in the making of steel rule cutting dies.

here is one source:

   http://www.mccauseylumber.com/specialty.ht m

Jim: MDF probably seems cheap because it is cheap. That's the main thing I like about it. Honestly, if good baltic birch ply didn't cost between 3 and 5 times as much as MDF of the same dimensions...

Still, for some things (binding jigs and the like), I do use ply. But since I'm not a pro, MDF is more than good enough for what I do with it.

My technique for laminating two pieces of about any material that isn't quite flat is to mate the convex surfaces with each other.   My thinking is that the two opposing forces tend to cancel each other during clamping to help flatten the end result. On large sheets such as radius forms, this also gives the advantage of only needing clamps around the perimeter as the middle areas of the plates mate up first.
Nelson

For almost thirty years my main solera has been a baltic birch finnish plywood (19 mm) to which the outer plays on both sides are phenolic. The edges are then sealing by a banding of 1/2' thick phenolic.

I was building guitars at night and working in a patternmakers shop during the day building wood patterns for injection molded plastic components and the phenolic ply was the best quality baltic ply with a heat and chemical resistant phenolic outer plys. It was super tough and all of the jigs and patterns we built from it really lasted despite taking a beating. For smaller parts we used solid phenolic bar and round stock.

I only mention this as it is not only the phenolic ply made of the best finnish ply, it is also tougher. Geza Burghardt is a perfectionist and at the same time that his students are building guitars they are also realizing that luthiers are toolmakers are much as they are specialized woodworkers. All of his jigs are made of phenolic ply. I dont know of a source as what I have and used are scraps from patternmaking but I am sure that there are sources out there.

After almost 30 years of building on my main solera, its shows little to no wear and has remained stable so if you are looking to build the ultimate jig, tool or solera, it is as stable as I have found.

Actually at the link to McCausey Lumber, right below the dieboard, is the OBO-Presswood (Festholz) which sounds almost identical to the phenolic ply that we used for patternmaking. In the brochure about it, it shows it in use for patternmaking just as I remember it.Shawn38912.8329050926