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I just saw something in another thread, did not want to hijack. How many people wrap their wood in foil before bending? I wood assume there would be paper on wood, then aluminum. I would judge aluminum against bare wood a bad idea (chemically react under heat and pressure).

Does it help?

Mike

craft paper first, then foil... Works for me...

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

I also do brown craft paper then foil, but not a foil wrap. Just a sheet of foil.


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Wrapped in parchment paper, lightly misted, in between two SS slats, blanket on the bottom.

B

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My memory is so good, sometimes I remember things that never happened.

I do paper towels ... light mist with water then wrap all that on foil to make a steam pocket.


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Brown paper, lightly misted, stainless slats, heat blanket on top. Fox style bender.

Spring steel slats covered with foil, misted wood and moist brown paper.

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

Non stainless ("Blue") spring steel slats, alu foil, heavy wall lining paper wet/moist, wood.
Alu foil keeps the steam off the steel which will stain/rust.
Don't wrap the alu foil, want the wood to have a chance to dry out when setting the bends.
Don't want alufoil in contact with some wood, especially Koa (green stain)

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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.

Sooo, the thinking is that the foil keeps the steam somewhat contained? This is interesting. Never thought of that.

Because I'm in Hawaii I work mostly with curly koa. A lot of curly koa does not need anything more than the wet paper wrap and some aluminum flashing backing with the blanket over that. Once you've worked with different kinds of curl, it's pretty easy to guess if there is trouble ahead or not. I have been trying the aluminum foil on wood that looks trouble some. It does make the bending safer, but causes me other problems. I get pretty severe staining on the bottom side of the wood. Can't be sanded out. It is not like the staining caused by a reaction with metal. Mostly heavy brown stains.Very little on the top. I've tried several different wrap techniques. A complete wrap. A wrap that is open on the ends. And a wrap that is open on the sides. The staining happened in all cases. Would like to get a solution.

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“ The meaning of life is to find your gift and the purpose of life is to give it away” Pablo Picasso

We use kraft paper and aluminum foil - the foil is primarily a barrier to moisture getting to the spring steel bending slats, which would tend to rust otherwise, and the kraft paper is a sponge in which we put a controlled amount of water for the type of wood we are bending. We cut separate sheets of foil (splitting a standard 12" wide sheet in half using a slat as cutting template) versus use a wrap, as we want the wood to be able to dump the moisture it's picked up during the 30-40 minute drying cycle after the bend. Envelope-type use of foil can also mark softer woods like mahogany as the foil bunches up, although this usually sands or scrapes out without issue.

Koa can react with aluminum, but the kraft paper barrier is usually enough to prevent this. Speaking of paper, we also use white kraft paper when bending woods like holly, as brown kraft can lightly stain some woods (although it is only visible on nearly white woods like holly). For woods like rosewoods which dump quite a bit of resin, the damp kraft paper acts like a sponge to soak it up, and eliminates most of the resin cleanup needed on the surfaces of the wood and slats.

One note on parchment - almost all parchments are silicone-treated, which in a bizarre twist is considered more eco-huggie than other treatments that use isoproponol/chromium-based coatings, such as DuPont's Quilon. While we don't believe the silicone is mobile during the bending process, it does prevent the paper from absorbing moisture, which would defeat the purpose of using the paper in our approach to the bending task.

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For the times they are a changin'

- Bob Dylan

I know this is off-topic a little but what temperature do you bring your wood up to you during bending and do you hold it at that temperature for a prolong period of time

I’m sure people who know more about it may have species specific temps and times, which would be great to know, but I generally do 250-275 and bend pretty immediately.
I kee it in the bender allow it to go to room temp then ramp the temp back to 250 once more and allow it to cool.


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This is the idea I was taught by a classical builder friend of mine yes.


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We bend as soon as we see steam rising from the bending package (another reason not to use an envelop), which gets the bend done prior to the moisture being exhausted. For a blanket bender, starting the bend at this point allows things to be completed and tied down in 8-10 minutes, at which point we allow the temp to rise to final temperature for the wood or until we see moisture exhaustion.

Most of the bad bends/broken side we see with former students come down to waiting too long to bend and allowing the moisture in the paper and wood to be exhausted. Rosewoods generally don't have this problem, but for woods like mahogany, ash, cherry, and anigre, getting the bend started as soon as possible and finishing before the moisture reservoir is exhausted gives a problem-free bend.

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For the times they are a changin'

- Bob Dylan

I also start the bend when there is a lot of steam rolling off. That usually equates to +/- 260. It is usually around 300 when the bend is finished.

I keep it around 300 for 10 minutes, allow to cool to room temp and reheat. It seems to work for me so I have not changed for a long time.

The damp brown wrapping paper and using two blankets were game changers for me. John Mayes suggested two blankets, don’t know who came up with the paper trick but it’s a good one.

I should note that I have only bent Mahogany, IRW and BRW, Maple, and Koa and with Maple and Koa all double sides so thinner pieces.

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

Been bending about 200 sets a year
I don't use foil and I stopped using Kraft paper.: The different suppliers may actually turn wood green so I now use butchers paper ( white untreated) also I use windex , thanks to a tip from Bob Gleason. Ammonia was used to help bend wood in the old days. I use this and no long find a need to use Super Soft.
My stack is using stainless steel slats

Slat wet paper wood wet paper slat and then blanket

I place a thermometer between the top slat and blanket.

Once I Hit 270 F I will do the lower bout , then the upper and do the waist last. I allow the heat to rise to 375F then set to
250 F for about 10 - 15 min.
Allow to cool

it is also worth noting I thickness to .075 in.

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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

Lots more experience than I have already posted. But for what it's worth, I spritz the wood, and then wrap in foil. I use the blue steel slats, so they do get a little rust going that I don't want on the wood. I can hear the steam being created. Start the waist bend to half way at around 220, lower bout around 275, and the upper bout at about 300. Crank the waist down the rest of the way. Run it up to around 320 and let it cook for about 10 minutes, then cool all the way down. If I'm patient enough to wait overnight, I have almost no spring back. So far so good.

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Tony Thatcher
Bozeman, Montana

This is obviously a huge subject and one that we beginners have huge trouble with (I am a cutaway convert) so without wishing to turn this into a mammoth thread I have two questions:

Woodie you always give us rational, experienced answers so when you say you use a controlled amount of water in your paper linings I wonder just how much that tends to be?

John, two things: your temperature is fairly high - I use mainly maple and I tend to get scorching at anything north 0f around 250. Any thoughts on that? And for a UK member what is Windex please?

Cheers Dave

I can tell you no the temp is not high the amount of time is what can cause scorching. I have never scorched a set of maple with this method. Are you talking F or C because I am talking F temp. Windex is a window cleaner here in the states.
I have been doing this for about 20 yrs and bend about 200 sets a year. CF Martin bends at 400F for about 6 min and no scorch so maybe you are talking a C temp.

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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

Be aware, some formulations of window cleaner do not use ammonia. I defer to John... wiser than most. But temperatures should depend on wood variety? I have never heard of using Windex. Just straight off the shelf? Do u let is soak for 12-24 hours? What about just using straight ammonia diluted? Windex has dyes....

John, do you have a way of setting the temp? Or do you just know where to set the knob on the contoller?

I use a thermometer I don't trust settings

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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 use widex right off the shelf and no soaking just spray and bend. We will be shooting new videos shortly to show the new technique.
I find that the temps can be used across the board. The one thing is that some woods like less moisture than others. Maple and Mahogany especially like less moisture. You won't hurt the wood even up to 400F for a short time. Lace wood will scorch faster than any orther woods but even that can handle 350
In all I am done heating in about 7 minutes
it takes me about 4 min to bend from the time I turn on the machine and about another 3 to reach my desired temp. Also thickness of the wood will come into play. I seldom bend thicker than .075 +/- .005

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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've been setting my blanket for 310ºF for most wood and start the waist bend as soon as I see good steam starting to roll. Lower bout and then upper bout.

Slat wet paper wood wet paper slat and then blanket (I've tried it with the blanket inside and outside the metal slats and think I get more even heating with it on top of the top slat.

Maple gets less water, Ziricote gets a little more. Goncalo Alves fought me the whole way this last time, but still avoided any cracks.

I'm going to give John Hall's method a shot on my next set - Wenge I think.
Thank you for sharing.