plasma cutter circle cutting attachment?

I have a little plasma cutter. I'm certain that Hypertherm sells a circle cutting attachment for it, just as I'm certain I can't afford it. I want to make
one. I made a nice cutting torch guide recently and now I want to make one for my plasma torch. Anyone made one or know of a good online set of pics to making one? I'm looking for design ideas, don't want to reinvent the wheel.
Grant Erwin Kirkland, Washington
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I have a Hypertherm, the model that runs on 120volts. I don't use a circle cutting attachment but have used them with Oxy/Acet. cutting.
I don't believe Hypertherm makes the attachments, but the welding supply dealer will have the fancy ones with little wheels. My machinist friend purchased on with his much larger plasma.
I found that most of my plasma burning was of irregular shapes and soon found that I could make a thin template from 1/16" ply, with allowance for the tip radius. I then clamp the template to the metal with 'reach-over vise grips' and run my torch around the outside (or sometimes inside) of the template. I have also found that I can get a very good cut even with the tip running directly on the metal, no tip gap at all (unlike Oxy/Acet.).
--
My experience and opinion, FWIW

Steve
"Grant Erwin" < snipped-for-privacy@NOSPAMkirkland.net> wrote in message
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I use 1/4" mdf board for templates, works great.
I used clamps for awhile, but have since migrated to extremely strong magnets.
-Tom

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I guess I should have mentioned, most of my plasma cutting it stainless or aluminum for my boat projects.
Steve
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On Thu, 19 Jan 2006 17:27:12 -0800, Grant Erwin

Yes Hypertherm does make a circle cutting attachment. I built one for mine based on the pic of Hypertherms. The one thing I didn't like about Hypertherms is that they use a large magnet for the center. This limits the size of the hole that can be cut. I made mine with a magnet from a hard drive. I welded a little post of 1/2" stock to a small disc just big enough to cover most of the hard drive magnet ( I then turned and faced the disc so it was square). The post is about 3/4" - 1" tall IRRC. I then made a piece that would slide over the post out of about 3/4" stock. In this piece there's a 1/4" hole just above the top of the post in which the arm for the torch guide slides. A 1/4" bolt on top clamps the arm. On the end of the arm is a short piece of pipe that kinda fits the outside of the torch cup (I was in a hurry and didn't take the time to turn a better fitting piece). I welded a 1/4" nut to the side of the piece of pipe that the 1/4" rod arm screws into (this allows different length arms).
The only problems I've had with it is one magnet getting ruined from heat. But that was a case where I was cutting a hole in the end of a plate that had just been welded onto the end of a piece of pipe (thus it was hot already before cutting). Then the waste piece that the magnet was attached to fell into the pipe and it took me a few minutes to manage to fish it out. By the time I managed to get it out the magnet had been ruined. But it's easy and cheap to replace.
Hopefully you can get the idea from the above mess of words. I'm not sure when I'll have time to take some pics and post them.
Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook/index.htm
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On Thu, 19 Jan 2006 17:27:12 -0800, Grant Erwin
Old loudspeaker magnet (car stereo is good). Keep the magnet and the poleplate at the back. Epoxy a stud / bolt / pin to the back of it. Stick some thin plastic (or masking tape) over the front, so that the pole gap doesn't fill with grinder crud and lose magnetic flux.
Steel strip about 15mm wide. Cut a suitable length and drill one end with a hole to suit the pin. Bend a joggle near this end so that it clears the back of the speaker magnet and the rest of it is almost level with the steel being cut. Drill another hole (10mm, AFAIR) at the right radius. Drill more holes as needed.
For the deluxe version, make it adjustable. Don't drill for the pin, just leave the strip long there. Make up another bracket which is a folded square loop big enough to pass the strip through with a bit sticking out drilled to fit over the pin. Drill the top of the loop and weld a captive nut over it to let an Allen or winged bolt be used as a clamp.
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Another magnet might be on the base of a work light. I have the base only - sitting on the side of a surface grinder.
It might be useful someday on odd shaped material - but for now, my DHC CNC - variable height control (automatically) plasma table will cut designs when possible.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Andy Dingley wrote:

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Hum - me to - maybe.... :-)
Hypertherm 600 here.
I'd consider a tubular 'pencil' setup - such that the torch insulating barrel slides down and the tip is at the 0.10 or dragging mode. (Gouge or quad post). Have it slip around so the user holds the torch and walks around the outside or over from the other side and around in reach over mode. The center point is a real PITA - how to attach it - Maybe a strong magnet - and a pivit from it. That would not work on SS. So maybe a sucking point - something like a lab floor puller (for raised floor users). Or Window - yea - Window cutter - suction - beam sliding beam that is - lock to length and then the action end is whipped around with the hand.
Hum - Beam and a shell end so the torch barrel will pivot around.
I know - now cardboard cutouts :-)
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Grant Erwin wrote:

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On Thu, 19 Jan 2006 17:27:12 -0800, Grant Erwin

http://users.goldengate.net/~dforeman/circle_cutter /
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On Thu, 19 Jan 2006 17:27:12 -0800, Grant Erwin

I tried various homemade attachments, but was never happy with the accuracy. I often found it difficult to maintain angle and speed all the way around. It's a pain to keep the hose clear as the torch is moved around. So I made this
http://www.citlink.net/~wmbjk/images/winchturntable.jpg which works surprisingly well so long as you don't mind cutting out a blank first. Does double duty welding circles. Good for circles from the size of the turntable up to perhaps 2' or so (as far as the winch handle could be reached comfortably). Modifying the winch took a couple of hours. Here's a picture of a cutoff made when the original circle was a bit too large. 6" diameter, 1/8" material.
http://www.citlink.net/~wmbjk/images/circlecutter.jpg
Wayne
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wmbjk wrote:

I'm amazingly dumb, Wayne. I can see your pictures fine, but can you flesh out the details of operation a little? You rest the torch over the bent steel flat bar so the flame is at the correct radius, then pull the trigger with your right hand while with the left hand you crank?
GWE
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On Fri, 20 Jan 2006 09:56:25 -0800, Grant Erwin

You got it, that's pretty much it. I've used it perhaps a dozen times, a little differently each time. The bent piece for instance was for resting the MIG torch on while welding around (IIRC) a 1.25" pipe nipple. For cutting, the threaded rod with the nut on the end holds the tip of the plasma torch. For a quick circle you can just hand hold the torch, resting the tip in the nut (it's drilled to fit). For more accuracy you can bungee the torch handle to something. One advantage over the usual compass-style device is being able to adjust the torch angle, either to cut a bevel, or just to counteract the natural taper of a plasma cut. There's also a piece of square tube welded to the frame. That had an adjustable rod in it with a rest for welding around the circumference of a 9" circle.
Cranking the handle while welding or cutting is really easy. Because the crank is rotated faster than the table, you get good speed control that's instinctive.
That particular winch is the cheapest one that HF sells, and it's plenty good enough for the task. I already had it for another project, but I think they used to be on sale sometimes for $13. I can't remember exactly how I modded it, but basically you have to change from the drum rotating on a bolt, to having the bolt stick out one side and rotate with the drum. Grounding the winch itself works fine, current flows uninterrupted through the gear teeth and bushings.
I cobbled the thing together to see if it would get me by on a particular project, thinking that if the concept worked out then I'd refine it. Instead I've left it crude and think nothing of tacking on another attachment as needed. Since that photo was taken I cut out some circles that (I didn't notice beforehand) were slightly smaller than the rotary table. So now the table is a little smaller as well and has a plasma-cut edge instead of the lathe-turned one in the picture. :-)
Wayne
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