Plasma Circle Cutter

[Hilbilly]

I had a need to cut some 3" and 6" diameter circles in 1/2" and 3/8" plate so I scribed a perfect circle on a piece of plate and tried freehand. Won't do that again ------ I suck at freehand. So I googled circle cutters and found one that looked like it would suit my needs and made it. It will cut from about 1" to 12" diameter circles and does a great job. While making my first practice cut (no power) I quickly discovered that if I my cut involves the circle cutter hanging over the edge of the plate it will drop off the edge of the plate and hang up when it gets back to the following edge. I resolved this by adding tapped holes between each of the torch holes so that I could put a screw on the underside of the cutter and have the head rest on the plate, behind the torch. Worked great.

 

[Shield Arc]

Never seen a circle burner like that before. Very interesting!
If you're going to be burning a lot of circles, one thing that is very handy is a rotating table. Take an old car or truck hub, mount it on a stand. And place some grating on top. It is amazing how accurate you can cut circles with it.

 

[Hilbilly]

I got the idea / info from post #18 on this link.
Has anyone made there own radius cutter?
There are better systems but I made this because I had the required parts on hand. The center pin needs to be held in place which makes it awkward to try and walk the cutter around the circle. Your table would have made that a breeze. Alternatively I tried to stay stationary and swing the cutter around the cut, that way I would have to stop to move the hand I was using to hold down the center pin and once the pin slid out of the center punch mark when I was doing it. That is how you get an ellipse.

I really like your rotating table and that would be perfect for smaller pieces of steel. I was cutting my circles from a plate that was 8' long so rotating the plate would only work if I cut it down into manageable pieces first. If I find an old wheel hub I am definitely going to grab it and make one of those.

 

[LD1]

Anytime I have had to cut circles I use a piece of wire.

Use a fairly strong magnet that has a tapped hole in it kinda like this Threaded Through Hole - e-Magnets UK

Take the wire (string melts) and put a large washer on one end for the torch and a smaller one for the magnet bolt. Keep the wire taught.

I dont do a ton of circles though

 

[Big Barn]

A rotating table like Shied Arc's is on my 'to do' list.

Terry

 

[Industrial Toys]

I supplied a motor, right angle reduction gear, speed control and foot pedal to a friend to make a rotating table. All surplus stuff. He is a good welder but the stuff he does with that looks like done with a robot. I was always going to build one for myself, but in a sense it is just another thing to take up space. I never thought about using it for the PLASMA. Very good idea!

On that note, what about a sliding table to make straight cuts?

I've said it before. If I am destoying something, I can make perfect cuts with the PLASMA. When it counts, I always manage to screw it up! Somehow the torch allways sticks to the work and then breaks free.

 

[Shield Arc]

For making straight cuts, these two things work really well.

 

[Big Barn]

Here are my home made and store bought straight edges. Pictured in between them is my "fine adjustment" tool.

Terry

 

[Industrial Toys]

The problem with free hand is also, that in thicker material it is hard to keep the cut at 90 degrees. But if you build something that moves, like a carriage, how do you activate the torch trigger and keep it on?

 

[Big Barn]

The problem with free hand is also, that in thicker material it is hard to keep the cut at 90 degrees. But if you build something that moves, like a carriage, how do you activate the torch trigger and keep it on?

Build a track and carriage to hold torch at correct standoff and angle. Pull and use trigger as in normal use. Some controlled resistance could be incorporated to make travel speed more consistent. ....maybe.

Terry