tite bond softening temperature

brian64 · Post by **brian64** » Sat Dec 20, 2008 7:57 pm

Hello all,

I've been thinking about heat bending a 2-3mm top after the halves have been joined. Do you think I can heat the wood enough to make it more flexible without softening the titebond? At what temperature does titebond soften?

Thanks,

Brian.

kiwigeo · Post by **kiwigeo** » Sat Dec 20, 2008 8:39 pm

The glue joint will fail way before you get to bending temperature.

Kim · Post by **Kim** » Sat Dec 20, 2008 8:53 pm

Agreed, I don't know the temp off hand but it does not take much to soften TB. Why are you wanting to heat bend a top anyway?

Cheers

Kim

Allen · Post by **Allen** » Sat Dec 20, 2008 8:57 pm

Just what Kim said.

There's got to be a good story behind this. Is it for a bent top mando?

graham mcdonald · Post by **graham mcdonald** » Sat Dec 20, 2008 9:24 pm

You can happily put the bend or 'cant' into a bent-top mandolin/ mandola or whatever after it has been glued. The heat is localized and only has to be applied quite briefly. The main limitation is how much arch you put into the braces after the bend behind the bridge has been done. Any more than a 15' radius will cause the area below the bend (or cant) to bulge a little halfway between the bend and the tailpiece. The line of the bend will need to be cut halfway through on the inside to allow it to bend, and there is a good chance of some surface fracturing on the outside, but it doesn't seem to matter too much on a mandolin.

Any other sort of bending (what sort of bending?) will almost certainly bugger the glue join. Titebond softens well under 100C

cheers

graham

brian64 · Post by **brian64** » Sat Dec 20, 2008 10:38 pm

Thanks for the replies, guys. I guess it's back to the drawing board.

I was thinking (very early ponderings on this project) about getting an arch in the top, similar to the Selmer Macafferi. I've read that's done by bending the pliage before joining the halves. I'm more confident of a good join when the halves are flat. I'll either have to bend before joining, or reduce the arch to what can be achieved with cold bending with shaped braces in a dish.

Cheers,

Brian.

Hesh1956 · Post by **Hesh1956** » Sun Dec 21, 2008 1:32 am

Titebond (original) softens and releases around 145 degrees F.

Typically the woods that we use start to become bendable at around 280 F and up so you can see what would happen to that glue joint.

hilo_kawika · Post by **hilo_kawika** » Sun Dec 21, 2008 1:35 am

Hi Brian,

What is/was the purpose of the arch in this guitar? Any pictures or plans that show it?

aloha,

Dave Hurd
www.ukuleles.com

brian64 · Post by **brian64** » Sun Dec 21, 2008 6:30 am

David, the purpose of the arch is to get an archtop type guitar without the expense and wood wastage of a carved plate. It has been done with the SelMac instruments, but I beleive some bending is done prior to joining the halves in that technique.

Brian.

sebastiaan56 · Post by **sebastiaan56** » Sun Dec 21, 2008 7:24 am

Brian,

On the Selmer plans I have the soundboard is bent and then joined together. The arch is 8mm at the bridge, on a 398mm lower bout. The cant is 8 degrees. Is this what you have?

When I built the bent top mando I glued the soundboard, then bent the cant and finally added the bracing. I used epoxy and it was fine. In Graham's book he describes the process of cutting the underside of the soundboard before bending. The anticipated disaster did not happen, it was rather easy actually. Remember that the heat is only on the underside for a short period of time and the real thickness at that point is about 1.5mm so it bends quickly. I used my standard bending iron.

Someone will correct me Im sure but the inherent tension in arching the soundboard adds bightness to the sound as it increases the effective thickness of the soundboard.

graham mcdonald · Post by **graham mcdonald** » Sun Dec 21, 2008 9:19 am

If you are wanting to put in an 8mm arch with a canted top, I think you will have to bend the two halves first and then trim a wedge out of the centre join below the cant. This was the common way that the Italian bowlback mandolin builders did it. Making up a dummy in cardboard will help work out how much wedge has to be taken out. Cut out a full sized soundboard out of the cardboard, cut up the centreline from the tail to the cant and then attach the cardboard to a arched brace in front of the cant. The amount of overlap will be come quickly obvious.

This is putting a different sort of stiffness into the soundboard to carving an archtop soundboard. A Selmer Macaferri style guitar is a different beat from a carved archtop. The other alternative is to mould an arch using heat and moisture out of wood 6-8mm thick and then carve the graduations if you are looking for an alternative to a fully carved soundboard. If you want that French jazz guitar thwack the canted top with the arched braces is the go.

Good luck, and please post some pics when you get to that point. There are several of us who would be interested in seeing how it goes

cheers

graham

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tite bond softening temperature

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