Bending iron

Tom Snape said:
For purposes of heating the inside of a metal tube I don't think it matters much which kind of bulb you use. The bulb is simply functioning as a resistive heating element, and whether the electrical power going to the bulb or element is making heat or light, the tube should heat up the same for a given watt input. The surface of a halogen bulb is hotter than a similarly power rated incandescent because it's radiating its heat over a much smaller area.
Click to expand...
It matters because a halogen is smaller. Want to make tight bends in the waist or a cutaway? Good luck doing that around a pipe that will hold a 100 watt incandescent bulb.
 
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Matt Clara said:
It matters because a halogen is smaller. Want to make tight bends in the waist or a cutaway? Good luck doing that around a pipe that will hold a 100 watt incandescent bulb.
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That's a valid point. I heat my old bender with a propane torch for that reason. It's made from lengths of 2" aluminum and 1" copper pipe.

Bender.jpg
 
Matt Clara said:
I finally bought a fox bender; if I was starting over I'd be tempted by those Alibaba ones someone listed above. Making your own is a bit of a trial and error pain in the neck.
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I ended up buying the electric bender from S-M with the small diameter extension. It's seems safer to use but honestly I think my torch heated one works better, especially on the smaller diameter. I also do some bending on forms using heat blankets.
 
Here in the US, hardware stores have electric charcoal starters. It's a heating element that's not quite the right shape and not controlable. Both of these problems are fixable. The result is cheap-ish. And seemingly effective. I learned this concepts used here from somewhere on the internet. Don't believe me too much, as I'm new and a friend and I are working on our first ukuleles.

2 3/8” aluminum pipe from local metal shop, $10 it so? --I don't remember. We initially used it with a propane torch, clamped in a wood-jawed vice. I wanted to go electric so I'd be able to work inside my apartment.

Electric charcoal starter, $20. I put a hinge on two scrap 2x4s, filed a catch-groove in each, then plugged in the starter until it was hot and flexible and squeezed it in the "press" until it fit in the pipe.

Dimmer switch. $10. Plus 3 wire nuts and a switch box, $3. I cut the (unplugged) cord, wired in the dimmer, and tucked it all in the box.

2 bolts, 4 nuts, two lock washers. I got the fancy stainless steel ones thinking they'd conduct less heat, but maybe it doesn't matter? <$10. Drilled two holes and bolted it up.

Aluminum scrap to plug one end. 2 wood scraps with relief notches for two broccoli rubber bands.

And a vice. Or a series of clamps, levers, pulleys, spindles to hold it firmly in place. I might prefer to have it vertical next time I bend.

I spent a small amount of time dialing the temperature on the dimmer by judging the way water steamed off. Made a mark there and started bending. So far I've bent wood binding.Bender_00.jpgBender_01.jpgBender_03.jpgBender_04.jpgBender_05.jpgBender_06.jpg

Precisely $53-ish, give or take. Heats up in less than 15 minutes. This diameter works for the baritones we're building, but it looks like the heating element could be squeezed to fit a smaller pipe. Or it could be put an ovalized pipe for a tighter radius. It's quiet and I can stand at the end of the pipe without burning my nether bits, which is an advantage over how I was using the pipe heated by a torch. And the wind doesn't blow it out.
 
Nice set-up. That will work... My only advise I will add is to thin your sides down to about 0.065 inches (1.65 mm) or so before you attempt to bend. Sometimes people who are starting out try to bend wood that is too thick. Good luck with the baritone.
 
"whether the electrical power going to the bulb or element is making heat or light, the tube should heat up the same for a given watt input"

Not correct, see above

"The surface of a halogen bulb is hotter than a similarly power rated incandescent because it's radiating its heat over a much smaller area."

Correct
 
Yes I just properly bent the sides for my 1st ukulele today! My new setup is a 190W heating cartridge (16$ for 5-pack) in a pipe (24$) with a dimmer (17$). I start it on max to heat up then turn it down to the minimum on the dimmer (50%). For the pipe I got a stainless steel 'sanitary spool' pipe from Amazon. I couldn't find any pipe elsewhere. I think in theory aluminium is better as it's a much better heat conductor, but anyway the stainless pipe stays hot just fine. It heats up in about 2 minutes too. I got a 2 inch diameter one which has been okay for my concert ukulele (although eventually it might be cool to have a 1.5 or even 1 inch piece too).
Oh yeah I also got a 3-pack of teflon baking/crafts sheets for 10$. I cut up strips, wrapped them around the pipe and stapled them together. Protects the wood jaws well. And I cut off another piece to use underneath the side wood that I'm bending if it's going to be on the outside to avoid marring it.
 
Poul Hansen said:
"whether the electrical power going to the bulb or element is making heat or light, the tube should heat up the same for a given watt input"

Not correct, see above

"The surface of a halogen bulb is hotter than a similarly power rated incandescent because it's radiating its heat over a much smaller area."

Correct
Click to expand...

I wonder about that and standard candle form bulbs are also slim too. What ever incandescent bulb you put electricity into the output is going to be mostly heat *. Now if the halogen bulb is smaller in diameter then you’ll be able to put in inside of a smaller pipe and hence use what heat there is to gain a higher pipe temperature (‘cause there’s less pipe to heat up). Well that’s my understanding and if I’m mistaken then I’m happy to be corrected.
* https://en.m.wikipedia.org/wiki/Incandescent_light_bulb
 
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Graham Greenbag said:
I wonder about that and standard candle form bulbs are also slim too. What ever incandescent bulb you put electricity into the output is going to be mostly heat *. Now if the halogen bulb is smaller in diameter then you’ll be able to put in inside of a smaller pipe and hence use what heat there is to gain a higher pipe temperature (‘cause there’s less pipe to heat up). Well that’s my understanding and if I’m mistaken then I’m happy to be corrected.
* https://en.m.wikipedia.org/wiki/Incandescent_light_bulb
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The end temperature depends mostly on your isolation and time. You can reach very high temperatures in a well isolated environment and here the wattage only determines the time it takes. The size of the tube is determined by the use of the bender and would normally not be designed to just heat up better or faster.
A thickwalled tube would of course take longer to heat up but then be more stable and take longer to loose temperature when used.
 
Sporky said:
Yes I just properly bent the sides for my 1st ukulele today! My new setup is a 190W heating cartridge (16$ for 5-pack) in a pipe (24$) with a dimmer (17$). I start it on max to heat up then turn it down to the minimum on the dimmer (50%). For the pipe I got a stainless steel 'sanitary spool' pipe from Amazon. I couldn't find any pipe elsewhere. I think in theory aluminium is better as it's a much better heat conductor, but anyway the stainless pipe stays hot just fine. It heats up in about 2 minutes too. I got a 2 inch diameter one which has been okay for my concert ukulele (although eventually it might be cool to have a 1.5 or even 1 inch piece too).
Oh yeah I also got a 3-pack of teflon baking/crafts sheets for 10$. I cut up strips, wrapped them around the pipe and stapled them together. Protects the wood jaws well. And I cut off another piece to use underneath the side wood that I'm bending if it's going to be on the outside to avoid marring it.
Click to expand...

A bit more elegant, than a dimmer, would be to use a thermostat/temperature controller. You will get heating up at max. power and then a stable temp. which can be preset. Typically +-5C

And you could set an alarm for too high temp. or for when the bender is ready to use :)

Amazon Best Sellers: Best Temperature Controllers

Discover the best Temperature Controllers in Best Sellers. Find the top 100 most popular items in Amazon Industrial & Scientific Best Sellers.
www.amazon.com
 
Is it of any benefit to stuff the aluminum tube with some kind of heat conducting material (like foil, maybe sand?)?
 
Poul Hansen said:
Sorry, just the opposite. A halogen lamp is more efficient than an incandescent. I.e. it produces more light(and thus less heat) than a standard bulb for a given power consumption.


"An incandescent lamp, which is fairly inefficient lighting, only has around 2% efficiency. This means that a 50-watt incandescent lamp produces only one watt of light and 49 watts of heat.

Meanwhile, a halogen lamp is a bit more efficient as it provides you with 7 watts of lighting and 43 watts of heat for a 50-watt lamp."
Click to expand...
If it's inside a pipe, the pipe will absorb everything it emits anyway, so it really doesn't matter. Resistive heating is inherently 100% efficient.
 
Mike $ said:
I built a bender with a piece of tailpipe I got from autozone for less than $10, and old disassembled lamp with a 100W bulb and a piece of pine that I made into a dovetail box. Works great as long as the sides are thin enough. My mahogany soprano sides are about 5/64" and they bent like a charm. I soak the wood for a while and slowly bend the sides for 10-15 minutes, clamp them into a mould over night and voila, sides.
Click to expand...
Nice, a good thing about that pipe is that I bet it can be squished out of round to get different radii for tight and wide bends.
 
Here is another "Gas Fired" one..this method was used at the Kamaka factory before they upgraded to more modern methods, the sides were soaked in water first, then the operator pressed the sides to shape (in pairs) on the hot mould by applying pressure by hand with the steel roller and hot caul... that's my guess anyway....I quite like this one :)

12E937B2-C1DE-40F3-90DF-862AF30EDD1A by Ken Timms,
 
I haven't bent a side in 4 decades, but when I did, I bought a piece of 2" or 3" copper pipe about a foot long at the hardware store and used an acetylene torch to heat it. I soaked the sides for a couple of hours in the bathtub before bending.
 
My neighbor built me this for a bottle of champagne and a bottle of Aperol. A little scared to try it out. Wish me luck! 😆
 

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