View Full Version : lathe-powered plasma cutting!

04-25-2005, 09:00 AM
ok so maybe this is a dumb idea.. but it doesn't seem dangerous, and IT WORKS..

i spent all day yesterday building a linear slide with complicated(?) screw and variable speed motor drive.. it was going to be a motorized guide for my plasma torch and would make super fast clean cuts.

anyway some wobble in the junk bearings and old screw gave me saw-shaped cut line (the same pitch as my lead screw!).. so i started again today to make a better one, seeing that the idea, at least, seemed to work.

when i realized i had a great variable speed slide in the shop already.. the lathe!

took me all of about 20 minutes to rig up a 3' long tube, bolted to my saddle, with a turned and welded seat on the end (to mount my handheld torch).

i figured 3' away was enough to keep sparks from the lathe.

so i dialed in the feed rate and CLEANLY CUT a 1' piece of 1/2" plate *without* tripping the power!

hmm.. now if i could only figure out a way to mount the torch in the lathe chuck and cut circles... http://bbs.homeshopmachinist.net//smile.gif

(ps. the circle thing.. just kidding)
(never know)


i'm hooked, by the way, and have my sights set on building a CNC plasma cutter. (thanks john and ibew).. heck, at this rate, i could just convert the lathe!

04-25-2005, 09:03 AM
ps.. i have a CEBORA inverter plasma cutter, though the 'top rating' says 12mm, i've never been able to make that big of a cut without tripping the power. 6mm is the most i ever used it for, and turned the oxy torch on for bigger stuff.

04-25-2005, 09:11 AM
Sounds like were thinking along the same lines.

I am putting together (in my head so far) a way to notch tubing with the plasma cutter.

Good luck!

04-25-2005, 09:24 AM
paul, for what its worth i had an idea a while back to cut fishmouths using the plasma, but i never followed up on it..

the basic idea was to mount to small 3jaw chucks next to eachother, on a plate, and gear them (chain on the backside, so they both turned the same amount)

one chuck would hold the tube to be cut, the other chuck would hold a 'template' tube, already properly fishmouthed.

the idea was to spring-load a torch holder so it could ride along the template, like a cam-follower, and copy the cut onto the blank tube.

of course you'd have to have 'templates' for each tube diameter and profile (angle).. small angles (ie long cuts) might be tricky to follow, though.


04-25-2005, 10:30 AM
You measure the diameter of the cutter tip, clamp a piece of angle, flatbar, or straight edge to the metal to be cut, hold the plasma cutter against it and press trigger and pull, holding the cutter against the flat edge. You end up with a PERFECT straight cut.

I also have cut out templates the size plus radius of tip. Lay the cutter nozzle inside and trace the template pattern and you have a duplicate. I cut fifty or so tattoo machine frames to hand break and polish (the part I hate). Installing some instruments at TVA I swapped the use of my plasma cutter for some man-hours on my timesheet. Same deal. On about ten jobs since then I have used a plasma cutter instead of jig-sawing/vibrating out control panels. (I got the tattoo-hand and a artists eye)

If ya was really sharp, you would fold a piece of metal around your tubing, make a template, clamp and cut your "fishmouth". I bought a jig jointer (hole saw on mandrel) from Speedway at $75 and love it.

I rotated the metal recently, I needed a bunch of circles cut out, build a arbor drive and 5-holed drilled and tapped spindle. Using CCW's waa-waa pedal to control the speed I got the metal hot, pierced and pressed the go pedal. You only need a single hole in the middle of the plate to rotate, my 5 holes were overkill.

My Miller plasma cutter is old. It keeps on clicking and cutting thou. It won't cut 1/2" metal.. I think 3/8" is max.

If ya want pictures I can repost them.. I just looked and have deleted them in the past.

04-25-2005, 11:25 PM
Bought a 600:1 gear box off ebay. Was thinking something like this:

04-26-2005, 03:42 AM
I'm not familliar with that machine - does it have a high frequency starting circuit? If so, it may be unsuitable for CNC; as the EMI will wreck havoc with your control...

04-26-2005, 07:17 AM
Paul, I've cut hundreds of notches with my plasma cutter (stock car cages) and a jig I made up.
It's a piece of pipe that slides over the end of the tubing and is shaped like the notch, minus the size of the cutter nozzle of course.
Has a bolt that tightens it to the tube and an index mark so they are all the same.
What I really like about it is that you don't have to be dragging long pieces of tubing around and trying to stick them in a jig etc.
I use a barrel stone on an angle grinder to give the notch a quick cleanup.

04-26-2005, 10:03 AM
I am not that good bending tubing I guess.

I notch to length. Fishmouthing, now that is easy for me with the jig jointer. BUT, beveling a tube for a consistient weld around kicks my butt, I end up taking the guard off my 4" grinder and standing on my head.

A air tool with a rotary burr would be much easier perhaps? Can you post pictures the next time you make a joint in a tubing?