Official Luthiers Forum!

When drying out your bent sides (just after they have been bent), while still on the bending mold, what do you find is the max temperature you can keep the sides for the next 45 minutes without leaving scorch marks?

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Formerly know as Mandodiddle.

I think it may depend on the species of wood.

A number I’ve heard bandied about is 280 for the cook off phase. Still hot enough to evaporate the water, but definitely not hit enough to scorch.

I researched this a few years ago and it seems that 300 degrees F + is the temperature at which there is a danger of charring/scorching occurring, but this is time dependant.
250 degrees for 15 minutes then cooled, repeated 3 times and left in the form overnight seems to dry my sides out and "set" them.

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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.

I don't ever use a 45 min time period .

I can tell you that most woods will bend nicely at 250F to 275. Also the thickness is a variable. I do mine at .075 in. Within 4 minutes I am done with the physical part of bending using a 5 watts per sq in blanket. At this point I allow the heat to go to 375F to 400F then after that I do a 15 min cycle at 275F.
Scorching happens with heat and time so the higher the heat the faster the scorch. You can check to see how the bend did by lifting your lower bout side of the bender and see how well it stays on the bending pattern

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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

I have mostly built with Maple B&S and scorching is much more of an issue. I have moved up to about 120 C (250 F) as a bending temperature and no higher for setting. (much as John Hall says) Any higher and things tend to go brown. Other things like thickness and amount of water, speed, as John says come into this.

I think, as many people have said this bending thing does seem more of an art than a science. Different techniques work for different people. A bit like the whole guitar building thing I guess!

Dave M

To me the real problem is 'how hot is the wood really getting". The wood can get hotter in spots than your readings tell you. That is why you always want to watch for steam and make sure it is not smoke. The eyes and nose are more reliable than a random temperature read. So it comes down to what temp do I want my setup to reach? It could be 320 F or so or it could be 275 F on your particular set up.

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Joe Beaver
Maker of Sawdust

there is one thing I think we are missing in this discussion
A I never measure wood temp
I want to the the temp of the blanket
B that is the heat that will bend the wood
the moisture in the wood will act as a refrigerant . As the moisture cooks off the wood will
get hotter. While I do watch for steam once you smell smoke it is too late.
C the blanket should not be allowed to go above 400F so if you are not using a controller or thermometer at least you are only guessing.

There are many techniques to bend wood putting a probe of hot wood for any length of time will leave a mark
Infra red heat measuring devices will be fine. After bending a few sets you should be able to dial in your skills

D time the actual bending needs to be complete in about 4 minutes
after that you can hold the temp of the blanket at 250 F without any issues . After 15 minutes you are done.

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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

I place the blanket between the form and the side. If I have scorching that won't sand out it is at least on the inside of the guitar.

Same for me Clay, and I go a step future. I use one of those small repair blankets under the waist. I only heat that blanket and bend the waist into the form (I know many will be aghast at that) then I unplug that blanket and spray some water into the waist area to cool it. Next, I plug the main blanket in, heat 'er up, then commence to bend.

On my rig, after bending, I set the temp to 275 and cook it for 10 minutes or so. All the while I keep an eye on the top slat temperature, (the one just above the wood) with a laser heat sensor. I like to see it no more than 225 F. I also monitor the temp between the blanket and bottom slat with a thermocouple. That is set for 275 F

One note on placing the blanket below the wood, the blanket will drop away from the wood. When I am ready to heat the wood, I pull the bottom slat up (the blanket is above it and below the wood) and clip it to the top slat with clamps.

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Joe Beaver
Maker of Sawdust

I have a temperature controller and I put the thermocouple on the blanket as John mentioned. When I was first starting out I noticed that this important detail was seldom mentioned.

My bends are usually done in less than 3 minutes since I don't have the Fox type bender where the "sandwich" is floating around. All my steel slates and blanket are locked down in my bender so I can cut the sides to exact length, then register and lock the tail end in the bender before turning the blanket on. It is nice not to be handling those sharp-edged slates.

John Mayes' videos from years ago said scorching starts at 320F. So maybe its best to stay 300F or less as Michael mentioned above.