Two coils in parallel for tapers?

[todoned]

My new induction heater is great! Many thanks to Grant! The speed is something you have to experience to really get how this will change the way you work forever. At least that's how I feel after using it for three or four hours, :-)

One problem I am having, is when I go to taper a bar, the tip becomes very difficult to heat... now this is partly a good thing (it is easy to burn a piece in half as I discovered) but kind of a pain...I find myself sticking the tip of the taper in the coil and waiting...waiting... it just doesn't get hot -- too far away from the coil I guess... mostly it gets hot by proximity. I have considered setting up my gas-saver and torch for just the purpose of heating the tip, and that might be a decent solution..but I wonder if there is another way? Either a technique to get the tip hot, or... and here's the crazy idea, running two coils in parallel...one very small used just for heating very small sections (e.g., the tip of a taper) alongside the regular one. I'm imaging some sort of machined "T" in copper that splits the current and the coolant...maybe give up a bit of the high end speed, but gain flexibility. Anyone tried this? Or have a solution to heating the end of the taper in the coil that was ideally sized at the start, but not so good now that its been pointed.

Thanks!
-Tod

[Adam2519]

I remember seeing a flat pancake style coil used to heat a bar held close to it without having to insert it in a cylinder. can't remember which post it was in. maybe something like that on a slight tilt to fit the profile of the taper would work.

Adam

[pkrankow]

Is there a reason not to have a couple smaller loops on the end of the larger continious coil? Just stick in a little farther and the coil is smaller where you need it.

Phil

[John B]

My new induction heater is great! Many thanks to Grant! The speed is something you have to experience to really get how this will change the way you work forever. At least that's how I feel after using it for three or four hours, :-)

One problem I am having, is when I go to taper a bar, the tip becomes very difficult to heat... now this is partly a good thing (it is easy to burn a piece in half as I discovered) but kind of a pain...I find myself sticking the tip of the taper in the coil and waiting...waiting... it just doesn't get hot -- too far away from the coil I guess... mostly it gets hot by proximity. I have considered setting up my gas-saver and torch for just the purpose of heating the tip, and that might be a decent solution..but I wonder if there is another way? Either a technique to get the tip hot, or... and here's the crazy idea, running two coils in parallel...one very small used just for heating very small sections (e.g., the tip of a taper) alongside the regular one. I'm imaging some sort of machined "T" in copper that splits the current and the coolant...maybe give up a bit of the high end speed, but gain flexibility. Anyone tried this? Or have a solution to heating the end of the taper in the coil that was ideally sized at the start, but not so good now that its been pointed.

Thanks!
-Tod

You have not stated what sizes and lengths of bar/tapers you are forging, clearance between coils and work etc.

Have you tried reciprocating the material when it is in the heating area, this would allow the concentrated heat to 'walk' to where it is needed

No doubt Grant will come in with a solution, Have you asked him yet?


You may also have to alter your methods of forging, induction heating is not like a forge, it is used in a specific application within a localised area, different sizes for different applications, it may be that you have to introduce new methods/sequences of working, more akin to production methods doing a single operation, concentrating on one stage at a time, rather than trying to finish one item off completely at a time. Bit of a learning curve here I think. Edited October 12, 2010 by John B

[todoned]

I agree its a different way of working. I was working (guess) 3/8" round in the smallest coil. I found I could do quite a lot by passing the bar through the coil, even when I had it all coiled or scrolled up. I guess I'm just wondering what others are doing to try and avoid coil changes. Tightening the coil at one end is probably a good solution if the only thing I was doing was tapering -- even there though, you might find that you need more length than you have. I have not built my pancake coil -- something I should do soon. I did try reciprocating, rotating, etc., the tip...all to no avail. Once these things come way down in price, I predict blacksmiths will own several of them, just to run different coils...

Thanks for the ideas,

-Tod

[Nakedanvil - Grant Sarver]

Actually the problem you are running into is frequency. This machine will do a maximum 100,000 cycles. 100khz has what is known as a "reference depth" of about 1/16 inch. This means that material less than 1/8 inch thick can only heat to the non-magnetic point (1450 or so) because the surface fields cancel each other. Heating from one side with a pancake coil allows you to cut that in half.

Look at the coil in this video for the answer to your other question. You can do coils in series or parallel:

[monstermetal]

Watching Darryl in that video made me wonder about slivers. Seems I am always digging bits of metal out of my fingers. Is there enough mass in a sliver you can get it hot when your finger is close? I understand the cross section/freq bit even if it just got a few hundred deg it seems like that would be a bad thing...

[Nakedanvil - Grant Sarver]

Great way to find them pesky slivers! Don't have to worry about them getting infected either.