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As I laid up and got side ready to bend today a thought occurred.
If going thru the trouble of making a sandwich, why not put another slat of wood in there and simplify things?

Spring steel, kraft paper, wood, paper, wood, paper, blanket, steel
OR
Steel, blanket, paper, wood, paper, wood, paper, steel
or
Steel, blanket, paper, wood, paper, wood, paper, blanket, steel
Or
Steel, paper, wood, paper, blanket, paper, wood, paper, steel

Does anybody do this and if so, how do you make your sandwich?

I would question whether the second piece would get the same heating that the one close to the blanket does. And so what, you've gained one day on me - I do one side, let it set in the bender over night, clamp it in the mold, do the second, ditto ditto, do the bindings. Put the bending machine away.

I take it out as soon as it’s room temp again. In winter I put it outside to cool like a pie and it’s ready in 30 minutes.

When I am laminating sides I will do both at the same time - block form,hpl, wax paper, veneer, wax paper, veneer, waxpaper,hpl, kerfkore, clamps. If I have previously laminated hpl on the block form and have a smooth surface on the kerfkore I will skip the hpl in the sandwich. When laminating with epoxy I leave the sides in the form for a week until the epoxy is cured. They then hold their shape for years.
For bending solid wood I place the blanket on the block form, clip the wood to the blanket with spring clamps. Lay the kerfkore on top and after heating the side for a few minutes start bending the waist, then bring the ends down and add clamps. I let it cook for a few minutes, then let it cool for half an hour. I do the second side the same way, then remove the blanket, replace both sides back on the block form , add the kerfkore and clamp them on the form until I am ready to use them. For resinous woods I might add some paper between the blanket and wood to keep the blanket clean, but generally don't. With the blanket underneath any minor scorching is on the inside and can usually be sanded off.

Only people I heard of doing that use a wide slat (~12"}and do them side by side, e.g. Trevor Gore.
If you stack them they would be a different shape.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

one at a time

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

The sides are being laminated one on top of the other and are reasonably thin. They both easily conform to the outside mold when fit to it. The difference in the shape is miniscule and not really detectable in the finished instrument. I would hazard a guess that they are more alike than even the best pipe bent sides, and in some cases more than individually bent solid wood sides.
I started doing them this way because I let the epoxy cure for a week before removing them from the mold. I didn't want to spend two weeks for a set of sides to be completed (although I have had some sets laying around for years before I used them). I will try to take some pictures and post them.
For solid wood sides I bend them with heat one at a time, as I mentioned. But if I am not going to use them right away I place both sides, one on top of the other, back on the block form place the kerfkore on top and clamp them down. When I trim them and put them in the outside mold I don't notice any significant difference in the shape. Solid wood tends to spring back and that might create greater variability in the shape than storing one on top of the other.

I took some pictures of a set of sides I recently laminated. They were a little thicker than most that I laminate, (.120" - 3mm) and had a fairly tight waist. I laminated them one on top of the other on a block form with HPL providing a smooth surface to laminate against. In the pictures I show how they were laminated (A on B) and then reverse them (B on A) and a close up of the small gap when reversed (C). The small gap would close with finger pressure. There is also a picture of the ribs not quite trimmed to size, but lapped over to show how they will look when assembled as a rim set. Finally there is a picture of a body I am presently finishing whose ribs were made in this fashion

I also bend laminates at the same time. No problems. I don’t put anything between them. It’s blanket- slat- paper- side- side- paper- slat- blanket- thin cover slat.

If you profile before bending I don’t think doing both at the same time with conventional sides is a very good idea.

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Terry and Clay, why do you laminate your sides?

Hi Dave,
The reason I laminate sides is I got a good deal on a few thousand feet of old (pre-ban) fancy veneers. They are "overages" from the wall paneling industry. I laminate matching veneers in the same order they were cut. The final product looks and acts much like solid wood. The old veneer is thicker, and I believe sawn rather than rotary cut. It eliminates a lot of thickness sanding, which cuts down on some dust but adds the glue up mess.
I still build guitars out of solid woods and don't notice any difference in the sound (Which means the laminated back and sides work as well as solid, or that I don't know how to get the best results out of solid wood).

I love the tonal effect of double sides. Good players I know seem to like the sound as well. Seems to work particularly well for me with Mahogany (same wood for both) and Rosewood with a Maple inner or vice versa.

I have been a little less impressed with all Rosewood double sides.

A fringe benefit is there is less chance of cracking difficult woods or tight cutaways. I use double sides on my archtops for that reason.

Trevor mentions how adding mass to a side expands the vibrating area of the top and I think the stiffness imparted by double sides does the same thing. They are all louder. The actual tonal effect may or may not be pleasing.

The most extreme example was a classical guitar that I saw that had a lead mesh laminated between two sides and a strip of lead inlayed into the lining.

It was super loud but the tone was terrible.

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It's not what you don't know that hurts you, it's what you do know that's wrong.