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Thread: Bending iron temperature?

  1. #1
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    Default Bending iron temperature?

    What temperature does the bending iron need to be? I assume there is an ideal temperature for the wood to bend with out scorching it to bad.

    Thanks!
    Sawdust

  2. #2
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    I always just turn mine on high. You can't scorch wood if it's spritzed with water. Have a spray bottle on hand and keep that contact area damp.

  3. #3
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    Quote Originally Posted by Allen View Post
    I always just turn mine on high. You can't scorch wood if it's spritzed with water. Have a spray bottle on hand and keep that contact area damp.
    Even spraying the wood with water I'm having trouble with scorching.

  4. #4
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    Quote Originally Posted by Sawdust View Post
    Even spraying the wood with water I'm having trouble with scorching.
    As you probably are aware of, different species of wood require a little adjustment in the temperature settings.
    Other than not enough moisture on the sides re-evaluate your methods.

    Maybe wet, wrap with wet parchment or brown shipping paper, wrap in foil to hold the moisture in (as in aluminum foil) heating blanket slats.

    Another, is the ability to read the temperature of the heating blanket as well as the whole sandwich.

    Adjust temps down after experimenting on scrap pieces of the same wood.
    Please forgive if all the above is known to you, good luck!

  5. #5
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    I am assuming that we are talking hand (iron) bending.
    It sounds like your applied spray is flashing off too quickly leaving the piece dry and susceptible to scorching.(Temperature may be far too high).
    I have tried to measure pipe surface temperatures with IR and bi-metal sensors but got such inconsistent results that I did not bother noting them.
    It took me ages to get anywhere near to working out the rights and wrongs of it. If you have never scorched, split, crushed or cracked a side while hand bending, then it will not be far off. Light coloured woods need extra care to avoid scorching. Very slight scorching on light coloured woods can sometimes be sanded out, but more often, not.

    From countless failures, I have gleaned that four main factors influence heat requirements:
    Wood type.
    Moisture - intracellular and applied.
    Wood grain orientation.
    Thickness of the piece.

    Initially, I had an experienced mentor who tried to help me to shorten the learning process, but I now concede that there is no substitute for 'just doing it'.

    Start low and build up the heat slowly ... the wood will either bend or resist. Once you feel a bit of give, increase the temperature slightly to a point where it will yield within a minute or two. If you apply more spray at this point, and work fairly quickly, you should be able to avoid scorching.
    Many people do not use applied moisture to assist in bending, but I can only manage that with very thin pieces like linings and bindings.
    Last edited by bazuku; 12-22-2019 at 02:21 PM.

  6. #6
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    Quote Originally Posted by bazuku View Post
    I am assuming that we are talking hand (iron) bending.
    It sounds like your applied spray is flashing off too quickly leaving the piece dry and susceptible to scorching.(Temperature may be far too high).
    I have tried to measure pipe surface temperatures with IR and bi-metal sensors but got such inconsistent results that I did not bother noting them.
    It took me ages to get anywhere near to working out the rights and wrongs of it. If you have never scorched, split, crushed or cracked a side while hand bending, then it will not be far off. Light coloured woods need extra care to avoid scorching. Very slight scorching on light coloured woods can sometimes be sanded out, but more often, not.

    From countless failures, I have gleaned that four main factors influence heat requirements:
    Wood type.
    Moisture - intracellular and applied.
    Wood grain orientation.
    Thickness of the piece.

    Initially, I had an experienced mentor who tried to help me to shorten the learning process, but I now concede that there is no substitute for 'just doing it'.

    Start low and build up the heat slowly ... the wood will either bend or resist. Once you feel a bit of give, increase the temperature slightly to a point where it will yield within a minute or two. If you apply more spray at this point, and work fairly quickly, you should be able to avoid scorching.
    Many people do not use applied moisture to assist in bending, but I can only manage that with very thin pieces like linings and bindings.
    Yes it is a hand bending iron, I made it out of a piece of pipe and a electric charcoal lighter, I have a rheostat on it to adjust the temperature. The wood that I'm trying to bend is 2.5mm thick.

  7. #7
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    That is too thick. I bend at 1.6 - 1.8 mm
    Bradford Donaldson
    Kekaha, HI and Cannon Beach OR
    bradfordj48@outlook.com

  8. #8
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    Yes, way too thick...

    Here are the physics of the situation as I understand them: When using moisture (water for instance) you want to keep the temperature just below the boiling point. Say you are going for 210 F (98 degree C) which is just below boiling point, to add a couple degrees does not accomplish much other than boiling off your water which defeats the whole process. The exception to this rule is with really oily woods like rosewood which have an intrinsic higher boiling point. People who bend a lot of rosewood will go up to 220 or even higher.

    Now I use an ammonia/water mix that has the advantage of a much lower boiling point which allows me to bend at a much lower temperature. Ammonia has the additional bonus of "plastisizing" the lignans in wood. I believe this is the active ingredient in the "stay-soft" wood products. I have been extolling the virtues of ammonia in wood bending for years and yet few use it. Why? Because people have found a method that works for them. You need to find that process that works for you. Also ammonia stinks and yes, it can stain.

  9. #9
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    Quote Originally Posted by BuzzBD View Post
    That is too thick. I bend at 1.6 - 1.8 mm
    Isn't that a little thin for a tenor ukulele? The sides on the Stewmac site are 2.38mm ( 3/32" )

  10. #10
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    Just measured a small batch of concert sides that I cut over a year ago, the max being around 1.9mm. Tenor sides from the same sawing session are around 2.05mm max. Final thickness sanding will bring that down approx 0.2mm.
    I find that every few points of a mm above this makes bending exponentially harder, particularly for tight curves. At 2.5mm you are making it very difficult for yourself, although there are techniques to make this easier (see Sequoia's post). Because of the insular properties of wood it eventually becomes impossible to apply enough heat to soften the piece through without scorching/charring it.
    At the other extreme, sub 1mm pieces seem to just melt around the iron in no time at all.
    If you suspect that thinner sides may be too flimsy for your builds due to grain anomalies or run out, you can always use 'popsicle stick' type side splints for reinforcement and split prevention.

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