Bending iron temperature?

Sawdust

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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
 
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.
 
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!
 
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.
 
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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.

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.
 
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.
 
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.
 
Isn't that a little thin for a tenor ukulele? The sides on the Stewmac site are 2.38mm ( 3/32" )

I could not find that spec on the Stewmac site. Please send a link... I've built a couple of Stewmac kits and my notes show the sides were around 0.065 (3/32 is almost a tenth of an inch or 0.1"). That is just too thick in my opinion. Plus who really cares how thick the sides are? They are the sides and not really acoustically active. I'm not saying you can't bend 0.1 thick wood, but why make it tougher on yourself than you have too?
 
I do most of my bending with a blanket and slats. I run my iron for touchup and bending headstock binding etc at around 400 F. Yes thats pretty hot and will scorch if you leave it one place too long but I find at that higher temp I can get my work done more quickly and don't scorch as long as I keep the wood moving.
 
No wonder you are scorching timber. Way too thick for sides on a uke. Mine are never more than 1.8mm.
 
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Mine's about 200-300C, but it has no temperature gauge on it so difficult to know for sure. The way to test if it's up to temperature is to drop little drops of water (from the water you're soaking the wood to be bent in) and see what happens. When the drops dance and don't settle before evaporating, you're there and ready to bend. :)

Also, as others have said above, 2.5mm is too thick. My ribs are 1.5 - 2mm depending on the instrument.
 
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I could not find that spec on the Stewmac site. Please send a link... I've built a couple of Stewmac kits and my notes show the sides were around 0.065 (3/32 is almost a tenth of an inch or 0.1"). That is just too thick in my opinion. Plus who really cares how thick the sides are? They are the sides and not really acoustically active. I'm not saying you can't bend 0.1 thick wood, but why make it tougher on yourself than you have too?

https://www.stewmac.com/Materials_and_Supplies/Bodies_and_Necks_and_Wood/Ukulele_Wood/Honduran_Mahogany_Top_Back_and_Side_Set_for_Ukulele.html

https://www.stewmac.com/Materials_and_Supplies/Bodies_and_Necks_and_Wood/Ukulele_Wood/
 
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Thanks for the links... Mystery solved. Backs, sides and top plates always come too thick and have to be sanded down to final thickness prior to use. It says, "thickness sanded" but that does not mean "final thickness" sanded. I have never purchased sides and top or back plates that were "final" thickness sanded to proper thickness. That part is up to the builder and thus the brisk trade in drum sanders and such. I once got some koa that was close to a 1/4 inch. Plates usually come in around 0.140 or more. Top plates of spruce can be purchased thickness sanded to about 0.125 which allows the builder to rout in a rosette before taking it down to final thickness.
 
If you are using a horizontal pipe, try laying a wet rag over it while you’re bending. Of course it’s imperative that you you keep spraying the rag to keep it from drying out. I do 95% of my bending with blankets but for the occasional stubborn spot that’s what I do. I’m also a believer in making my sides as stiff as I can without using splints so I bend at 0.090” for most woods which seems to be a comfortable maximum thickness for me.
 
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I have quit using my bending machine and heat blanket and find better success with a iron pipe with a commercial soldering iron inside. it gets to 260 max. I wet wood and bend under a stainless sheet. I find I have better control when feeling the bend, used to break sides fairly often with the machine. Hot pipe bending solved that problem. I sand the wood to .o80
 
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