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Thread: First attempt at heat bending: questions

  1. #1
    I really look like that soliver's Avatar
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    Default First attempt at heat bending: questions

    Hey guys, just gave it my first go at heat bending and I have a couple questions, here are the things to know first:

    A: building an A/N flat top with plans from Terry M from Crystal Forest Mandolins
    B: I'm using mahogany as my back and sides (why you ask?... because it was free)
    C: I am using a propane torch heating a piece of 1" black gas pipe (see pic for set up)
    D: I made extra sides because I assumed I might screw some up

    Questions:

    1. Is it no supposed to scorch this much?... regardless of how much water I spray on, it still scorched; is this a product of my set-up? Is this ok because no one will see it because it's on the inside? If not, how do I not let this happen?

    2. If I over-bend it, what's the best method for bending it back?... I tried turning it over and heating the outside and scorched the outside a little and am not sure it will sand out.

    Thanks in advance

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    aka: Spencer
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  2. #2

    Default Re: First attempt at heat bending: questions

    You should be able to bend without scorching at all, so it sounds as if you want to dial back that torch a good bit.
    This beginner with minimal gear uses a hot air paint stripper gun, but even that is too fierce on full power.

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  4. #3
    Registered User j. condino's Avatar
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    Default Re: First attempt at heat bending: questions

    Too much heat.

    A larger diameter pipe will also help.

    How thick is the wood?

    Bending with dry heat is an odd skill that not many woodworkers use. The secret to getting good at it is simple: practice bending with all kinds of different woods and you'll get the hang of it soon enough. I try to teach all of my students to go ahead and break several practice pieces so they can get an idea of the boundaries they are working with; every piece of wood will bend, burn, and break slightly different. Be glad it is a tiny 1" mandolin section; bending a 9" wide section of super curly maple for a double bass is brutal!

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    Mandolin tragic Graham McDonald's Avatar
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    Default Re: First attempt at heat bending: questions

    The usual thinking is that the metal pipe should be hot enough that water sprayed on should just bounce off. You can check this as the pipe heats up and it will get hotter at different parts of the length of the pipe as it heats. With a propane bottle like the one in your photo, the flame from from the torch does not need to be more than around 3/4" long. It is very easy to get the pipe much too hot, and such scorching is inevitable. Have a spray bottle of water close by and keep the strip as damp as you can. Keep rocking the strip over the pipe to the heat is not concentrated on a small section, Try to heat around 2" at a time and spray more water as the outside dries out. As James says just practice until you get the feel of it. It is not hard, it just needs some practice.

    Cheers
    Last edited by Graham McDonald; Jun-14-2020 at 4:06am.

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    Default Re: First attempt at heat bending: questions

    I’ve read that dry bending (or at least slightly moist bending) is used because it works better than steam on figured/brittle woods, causes less color change, chemical change and breakage. OK. Is there a list of ‘bendability’ by wood type and grain that’s useful for luthiers? Or are the pretty woods too variable to categorize? Also, for (production) pressed tops and backs - wet or dry?

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  10. #6
    I really look like that soliver's Avatar
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    Default Re: First attempt at heat bending: questions

    Thanks everyone... Graham, I am following your book but using different plans from the ones in your book... thanks for such a great resource! I love the set up you have in the section on heat bending, however I could not find a piece of 2" copper easily available, I may have to look again and try some plumbing supply locations, rather than the big box store. I chose the threaded gas pipe because a lot of guys on YouTube made that work, so I gave that a try.

    I was spraying the wood with water before applying it to the heated pipe... but long and short, it sounds like I need to dial back the heat. I may have to change my set up, I'm thinking my torch has 2 settings: on and off. I may be able to dial it back though; we'll see.

    Jim can you describe or show pics of the set up you used, I can borrow a heat gun from work if necessary.
    Last edited by soliver; Jun-14-2020 at 8:41am.
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    Registered User sunburst's Avatar
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    Default Re: First attempt at heat bending: questions

    I'll add that some (most?) mahogany bends easier after a short soak in water.
    As others have said, each piece of wood is different even within a species. Different amounts of moisture, different amounts of heat, different amounts of time on the pipe work for different pieces. As has been said at least twice, it takes a little experience to get the hang of it but it is not too difficult.

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    Default Re: First attempt at heat bending: questions

    I've never had a rim not scorch a little, especially around the scroll and the tight 'S' below the neck.. I use about the same setup as you but with electrical conduit... I've taken a strip of 1/2inch metal and folded it into a 'U' and placed it into the end of the pipe.. It keeps more heat inside the conduit.. You can lower the heat going into the pipe and saves the clothing if you get too close when bending.. Yes, each strip of wood acts differently , even from the same piece of wood.. And use as little water as possible and still get steam .. Get a feel for the wood as it forms, and practice.. and break a few to get the feel for when it is too much......
    kterry

  14. #9

    Default Re: First attempt at heat bending: questions

    Quote Originally Posted by soliver View Post
    Jim can you describe or show pics of the set up you used,
    Pretty much like yours, but with the hot air gun instead of blowtorch. I've tried both with a large diameter tube with the gun blowing through, and smaller with it blowing from the side. As the others have said, practice is key.

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    Default Re: First attempt at heat bending: questions

    I'm no expert but two things that I have think I have learned when it comes to bending are: First, you need to get the wood hot, right below the scorching point, where the fiber layers easily slide past one another. Second, thin the sides more where the radius of curvature is smaller. Usually tight curves are well reinforced by the internal blocking and thus can be thinner without risking weakness.

    I use a setup similar to yours except the pipe is a about 2 inches in diameter. I think that diameter pretty well matches the curvature of the neck block.

    I still have trouble getting a "fair" curve all the way around the longer sections.
    -Newtonamic

  16. #11

    Default Re: First attempt at heat bending: questions

    Here are a few cartridge heaters on my bench. I use these for unrelated products. They are available from $20 on up, choice of diameter and wattage. Also called rod heaters. 2” diameter thinwall copper plumbing pipe is also easy to get, but maybe you have to buy at least a foot. To get uniform temperature, I’d definitely use copper for the outside, and infill between the heater and the pipe with something called graphite cement, which is a good heat conductor. If you want to be fancy, run the heater on a dimmer for heat control, or a Variac if that’s sitting around. An in-oven digital thermometer can be embedded in the cement, and then you’re cooking!
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  17. #12
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    Default Re: First attempt at heat bending: questions

    Thanks everyone!

    I fiddled with my torch a little and found that if I crank it down practically to the point of it being off, the flame is around the 3/4" mark like Graham mentioned above.

    I'll also look and see if I can find a price of 2" copper and reconfigure.

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    aka: Spencer
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  18. #13
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    Default Re: First attempt at heat bending: questions

    Call me crazy, but I'm not a fan of open flames in woodshops. Long ago, I used a 4" copper pipe for guitar bending over a cone heater, running insulated, meaning asbestos insulated, wire. (it was a long time ago.) Can't buy that stuff now, which is good.

    I now have a bespoke electric bending fixture, like the StewMac bending iron. Its a lot safer and works just fine. I use thin sides, spray a little water and bending goes well. The more figure, the more difficult, ie, more breakage, but that's the price of experience. You develop strategies over time.

    Good luck.

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    Registered User j. condino's Avatar
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    Default Re: First attempt at heat bending: questions

    Home Depot electric charcoal grill starter; $16. 'Best secret heat source going for bending irons! You can bend it and mash it around to fit your pipe size.

    IMO, the Stew Mac electric bender is one of the worst made: overpriced and far too small diameter for anything but the smallest projects. It is similar to many of the electric hot hide glue pots that they sell for $150+ when a $3 thrift store hot pot works fine....



    https://www.homedepot.com/p/Electric...E&gclsrc=aw.ds
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  21. #15

    Default Re: First attempt at heat bending: questions

    That is a cool idea James.
    I could not get away from scorching with a torch and had the fear of fire that has been mentioned. Last item I bent sides I clamped my copper pipe over an inexpensive hot plate from Target or Wal Mart and it got it to the right heat with no scorching and no open flames. Copper definitely transfers heat better than steel conduit.

  22. #16
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    Default Re: First attempt at heat bending: questions

    Great idea James!... thanks!
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  23. #17
    Adrian Minarovic
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    Default Re: First attempt at heat bending: questions

    I made my iron out of galvanized plumbing pipe an delectric heater similar to what James posted - it was replacement part for some air heater or something that I found at local HW store. I used ordinary fine quartz sand (washed) to fill the pipe. One end welded (you can use common plumbing HW to close it), on the other end I made small lid out of thin steel sheet with few fingers bent to right angle and small hole for the wires and used metal ring to hold it in place. Has worked for me for last 20 years.
    Open flame in dusty woodworking place can be dangerous.
    Adrian

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    Default Re: First attempt at heat bending: questions

    I would suggest a bigger diameter pipe so that you can heat more wood at one time. Judging by the burn marks, it appears that you might have lingered too long on individual spots on too hot of a pipe. It's best to slide the wood back and forth along a larger diameter pipe at the right temperature - around 350-375 degrees. For years, I used a 2" diameter pipe and a propane torch. I got one of the expensive Stew Mac - Ibex bending irons after becoming frustrated trying to form the f5 scroll area with some nearly impossible to bend super curly maple. I thought about making my own bender but decided to just bite the bullet and get the ibex. An electric bender will distribute the heat more evenly, but a hot propane torch fed pipe will certainly do the trick.

    Figured maple likes to bend dry. Mahogany seems to like lots of water. Another trick is to take a wet paper towel or layer of cloth and put it between the wood and your iron. Let it steam up real good and you should then feel the wood starting to give.It will dry quickly, just spray more water on the towel. Don't rush it and go slow. Take several passes. It takes some practice to understand the concept. A metal backing strip also helps keep the heat between the iron and the wood. It also helps prevent splitting on more severe curves. You can see the large metal strip in the photos below. I have a small metal strip I made from roof flashing for mandolin sides.

    I'm working on a couple of mahogany L-00 style guitars at the moment with sides 2.8 mm thick. I was able to bend the sides easily using the Ibex bender on "7" (375 degrees?) lots of spritzing and a wet paper towel. No scorches whatsoever.

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    PS - I don't have an expensive glue pot. I have a $10 Presto electric kettle with a hole cut in the top for a small mason jar or to stick a squirt bottle in.

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  27. #19
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    Default Re: First attempt at heat bending: questions

    I am still using the same galvanized plumbing pipes I made up 27 years ago. I welded a 10mm steel rod to the pipes and clamp the rod in a vice to hold it. I have two pipes, one about 4" the other is 1". Propane torch heats it up. Basically, practice makes perfect. All wood species are different, some bend best if saturated, some bend best if wet on one side, some bend best if hardy wet at all, and a few will bend if not wet at all. Some will change colour if wet, so you then need to either bend dry or wet what will be on the inside of the mandolin. Graham gives a good explanation on how to determine the correct temperature. Don't leave the torch on the pipe all the time. That will only guarantee scorching, and it might not just be the wood you want to bend that will get burned! Heat it up to temperature and take the torch away and turn it down but not off. Then bend until the pipe cools. Heat with the torch again and repeat. Easy peasy after lots of practice. As John says, Mahogany bends easily if wetted so you should not get any scorching.

    I hear the concern about open flames in a workshop. I nearly set fire to the curtains once. Probably would have burned the whole place down. The curtains are now gone and the bending is done well away from anything flammable. You need to make sure all wood shavings scrap wood and sawdust is cleaned up before firing up the propane torch. Lacquer solvents, paint or alcohol should not even be in the same room.
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  28. #20

    Default Re: First attempt at heat bending: questions

    +1, you should not be scorching the wood. It isn't an instantaneous process. You are basically melting the "glue" in the wood which holds the fibers together. When it's warm, slip the fibers, and then let it set back hard again. That doesn't take much heat, just around boiling. Your flame might be 2000 deg F.
    Don't aim the flame at the "business" side of the tube, but at the opposite side. You want as even heating as possible, which would be better if you hit the outside of the pipe with the flame and let conduction do its business. A propane torch is 10-20x more BTUs than is needed for this job. My IBEX bender is around 100W IIRC, and my homemade silicone blanket bender is 250W.
    Slow, even heating wins the race.

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  30. #21
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    Default Re: First attempt at heat bending: questions

    SUCESS!!!

    Thanks for the guidance everyone!... before investing in a bunch of new stuff, (pipe, electric heaters, etc.) I opted to give it another go with what I have. I cut the flame waaaaay back on the torch and applied the heat indirectly by having the flame licking the side of the pipe rather than strait down the middle. I could tell the heat was in the right range because, as Graham said the water just bounced right off the pipe. I successfully bent the entire side without scorching it at all! I did try the wet rag, but that didn't seem to be working, so I abandoned it. You can tell the difference between last night's attempt and tonight's:

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  31. #22
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    Default Re: First attempt at heat bending: questions

    And Soliver #001 is well underway!
    aka: Spencer
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  32. #23

    Default Re: First attempt at heat bending: questions

    Quote Originally Posted by bpatrick View Post
    . I have a small metal strip I made from roof flashing for mandolin sides.
    The thin stuff, seems to be plated? Thanks, I've been trying to figure out what might be a good budget option for making a strip, seeing as metal stockholders only want to sell sheets by the acre, or that's what it feels like...

  33. #24
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    Default Re: First attempt at heat bending: questions

    [QUOTE=Bill McCall;1775591]Call me crazy, but I'm not a fan of open flames in woodshops.

    Side benders do cause fires. I have a folded steel "worm" inside my pipes. If they are shaped just right they help the pipe heat evenly.

  34. #25
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    Default Re: First attempt at heat bending: questions

    Quote Originally Posted by soliver View Post
    And Soliver #001 is well underway!
    Yippee! I hope you will post pix of your challenges and successes on your journey.
    New to mando? Click this link -->Newbies to join us at the Newbies Social Group.

    Just send an email to rob.meldrum@gmail.com with "mandolin setup" in the subject line and he will email you a copy of his ebook for free (free to all mandolincafe members).

    My website and blog: honketyhank.com

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