had a question on facebook about making your own coils, worth noting my reply here for others.

 

say you made a 1" coil with 100 loops in it, it would never produce any heat. a 1" coil with 1 loop would overload the machine and damage it. but with 3 loops would generate an immense amount of heat, melting anything you put in it in seconds. you *could* use that coil at half power and be ok but its better to remake the coil to say 5-7 loops and run it at full power. same temp as lower power but over a much larger working area.

Any opinion on multiple loops per fixture? What are the downsides of having a 3/4”, 1.5” and a 2.5” (or similar) on a single coil? That way you could have multiple size ranges without having to change coils. 

i havent tested the multi-loop coil thing yet, its REALLY hard to find metric flare nuts for this thing. I may end up doing a metric-->SAE conversion on this thing. i only have 2 spare flare nuts that fit the stock unit that came with it. 8mm flare, unknown threading/size. man I've been tryin though.

As soon as i have this flare nut thing resolved i'll make all sorts of coils including a levitation one and the multi-coil and post about it.

Mettle works has them 

You just saved me a bunch of work, thank you so much.

just ordered 15 8mm flare nuts from mettle works. neat site there's some good stuff on there. 

Our coils were soldered to copper blocks that were bolted to the head. They had push lock fittings that hooked onto the coil tubes. The head had sets of holes which allowed us to move the coils up or down depending on what setup we were running.

found an excellent coil design document http://www.stanleyzinn.com/pdf/coil_design.pdf

That is the same coil info that was given to me when I went to the Ameritherm training course. Unfortunately the company I worked for tossed the notebook during the move.

That's a great read. It will be something else that my wife looks at on the bedside table and shakes her head.

I am at work, so I can't really read it, but I don't see anything in there that indicates I can't run a reasonably efficient multi-loop coil. I need to pay attention to design, but it looks like there's no theoretical problem with it.

Didn't get any pictures of it but started a new piece yesterday for the wife's birthday - making 1084/15n20 knitting needles. Used a smaller billet about 1.5x1.5x0.75". Had to drop the power down just a bit, around 650 amps to keep the sides from melting but got a fantastic weld in 2 heats. Evenly spread out welding heat took about 80 seconds. Drew it out about 6 inches, zero delams looks fantastic. No flux used. Very pleased with its performance. 

Many improvements made in the last few weeks. I've rigged up a dual pancake coil and can now heat large items. Jeep CJ leaf springs for example heat up wonderfully.

You can also do a single pancake coil instead of two.  A little more involved in bending but it gives you total open space above and below.

built one of those first, works but doesnt heat nearly as fast as this double.

You are not size limited like a double though.

Have you made a coil that allows for levitation? If so I would like to see a video of it. Thanks

Great thread, thanks for sharing all the information everyone.