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lpr5184

Building A Better Bending Iron

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Atomino   

Well Ernie.

just check the diameter of the cartridge and start replacing it. A 250 watts one would be more than enough. I would put a Teflon layer between the "iron" and the wood and between the screws (and washers if any) inside the wooden box. I can't see a thermal probe hole. Guess the knob for controlling temperature is some kind of dimmer. Think you have to replace it even if somebody likes dimmers for the job. You can go digital, more expensive but more "professional".

Make a list of what you need and get started when you'll have all the "puzzle" pieces.

Ciao

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The temp control looks to be nothing more than a triac lamp dimmer. There isn't any feedback temperature sensing, so it's a "set by trial and error" kind of setup. If you want a thermostatic control, you could incorporate an electric frying pan cord / thermostat assembly such as this:

http://buyitnow64.stores.yahoo.net/sunbeamprobe.html97296n2big.jpg

I would put a sealed cartridge heater inside the bore, and make sure the iron itself is grounded for safety purposes.

You could mount the iron on a teflon base as suggested, or you could use high temp phenolic or asbestos board. If you choose the asbestos, get it cut and drilled for you by someone who knows how to work with asbestos and takes the proper safety precautions. You don't want to make or breathe asbestos dust. Get rid of the plastic box; Perhaps consider a Hammond die cast aluminum boxes such as this:

http://www.hammondmfg.com/pdf/1590UF.pdf

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If you are going to directly bolt the iron to that base, it's going to get just as hot as the iron. There really isn't any need to heat the base. To get around this, you need some sort of thermal insulator between the iron and the base.

When I made my Iron, I made the curve radii slightly tighter than any I would encounter on a violin. You need to over bend the ribs slightly as they tend to spring back slightly after the bending process.

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Welding is overkill. You can use bolts to hold it down and even help with isolation. I used PTFE washers on mine to help isolate the threaded rod from the box. I think something like that with a wood base is fine. The Ibex irons just have a sheet of something between the iron and the wood. I just used the project box as a time saver.

There is such a thing as too much mass. Mine is solid and it heats slowly and if you overheat it it takes a long time to cool down.

Mine is made to a shape that would allow me to make a small Andrea Amati if I wanted to.

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Atomino   

Yes, I think you don't need to weld a base. As it gets hot as the iron, you risk to scorch your hands while bending close to the box. If I should make another one, I would surely build it without a base. The pushing effort in bending violin and viola ribs is minimal, two M6 screws threaded in the iron will do just fine. I tried with PTFE but got melted over 140°C. Teflon stands until 250°C and I'm happy with it. Don't forget to insulate both the iron and the screws/washers, whatever material you chose for the box.

A 500 Watt cartridge heats up my brass "iron" in no time. Guess you can pick one between 150 and 250 Watts. Look for Watlow Firerod heating cartridges on Ebay.

Shape is ok. Bending correctly is a matter of adjusting the rib on the iron, you just have to do it getting accustomed to the available curves.

Ciao

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Hi Ernie, thanks for the comments.

If I understand correctly, you drilled and tapped four holes into the bottom of your iron? Can you tell me what size threaded rod or bolts you used?

10-32 stainless

Are the rods attached to the project box or do they extend through the box and into the wooden baseplate? I don't remember what material your project box is made from...is it one of the aluminum ones?

Rods just attach to the project box, which is aluminum. I think the weakest spot in my design is the small screw size that fits into the bottom of the project box. I used longer ones going through the wood from below to hold the box to the wood, SS for added strength so I'm not too worried that the thing will give way.

I'm not familiar with PTFE washers, what are they and where do you buy them? I'm also interested in knowing what type/size element you used in your iron. If I remember correctly, I think you said that you got it from McMaster. From what I understand 250watt is sufficient.

PTFE is the generic, Teflon is the brand. Or at least that's what I thought until I read Atomino's post. At any rate according to the specs at McMaster it's a good insulator. I got the washers from McMaster, along with the 250 watt iron which is plenty.

Too me welding a baseplate is much simpler than drilling and tapping holes, since I was a welder in my former occupation.

If you have a drill press drilling and tapping is a cinch.

I think CB Fiddler posted pictures of a disassembled Ibex iron showing the piece of insulation you referred to. It looked like it burned through to the wood.

Yes that was an eye-opener, but I still think the principle is sound--i.e. the way Atomino has it seems fine.

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Just be sure not to use oil-soaked bearings as bushings. I think in a pinch you could wrap the cartridge in aluminum flashing or sheet aluminum to make a tight fit. Or just use the 500 watt element if you can find a switch that is compatible, and keep the setting lowwww. :)

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Hard to be sure that it would matter what size cartridge you use. I used a 1/2" one. I think it's far more important to make sure your cartridge matches your switch than to worry about the size.

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The larger the diameter, the longer the element should last. Too much heat concentrated in a small area tends to lead to heater failure sooner. I chose a 5/8 diameter by 4 inches long, 250W for mine.

You could wrap brass or aluminum shim stock around the cartridge until it fits snug in the 3/4" hole.

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Yes, I think you don't need to weld a base. As it gets hot as the iron, you risk to scorch your hands while bending close to the box. If I should make another one, I would surely build it without a base. The pushing effort in bending violin and viola ribs is minimal, two M6 screws threaded in the iron will do just fine. I tried with PTFE but got melted over 140°C. Teflon stands until 250°C and I'm happy with it. Don't forget to insulate both the iron and the screws/washers, whatever material you chose for the box.

A 500 Watt cartridge heats up my brass "iron" in no time. Guess you can pick one between 150 and 250 Watts. Look for Watlow Firerod heating cartridges on Ebay.

Shape is ok. Bending correctly is a matter of adjusting the rib on the iron, you just have to do it getting accustomed to the available curves.

Ciao

Thats strange PTFE is Teflon??

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