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Old 09-29-2010, 09:48 PM
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Lu47Dan Lu47Dan is offline
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Default Circle cutter for my plasma cutter.

I need a circle cutter for my plasma cutter, so I had to engineer one from what I can make here.
The first part to make is the locating arbor for the pivot, the first arbor is for cutting the 3/8" round plate. This plate will make the bearing end plate and the mounting flange for the suction end plate. I was going to make the impeller plate out of that plate and the suction side end plate mounting flange, but there would be a large amount of waste in that configuration.
So I needed a way to center the circle cutter. This is what I came up with.
  1. Bottom half machined.
  2. Side view.
  3. Inserted.
  4. Cutting off after marking the height of the shoulder and overall length.
  5. Arbor finished.
This started out as a piece of 2" cold rolled round stock. The locating pin is 1.250" in diameter, the shoulder is 1.938", and the top pin is 1.000" in diameter with a 1/2" X 13 tapped hole.
The top pin is the anchor point for the circle cutting jig, the jig arm will be made up by a series of threaded rod. The anchor end and torch end will have about 1" of adjustment in them.
I will be making the torch end and the anchor ends tomorrow. Once I have the jig built I will be making two more pivot anchors for it, one will bolt on via a 1/4" bolt and the other will be held in place with a pot magnet.
Dan.
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  #2  
Old 09-29-2010, 10:10 PM
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Dang, Dan! How did you get that polish on it?
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  #3  
Old 09-29-2010, 10:30 PM
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Lu47Dan Lu47Dan is offline
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Cutter, the polished area of the arbor, the speed was 500-600 rpm, feed 0.022"/rev and depth of cut of about 0.032". At that diameter, the feed and speed must be just right to produce that finish. I made two cuts to get rid of the rusted surface.
I would like all my finished surfaces to look like that.
Dan.
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Last edited by Lu47Dan; 09-29-2010 at 10:53 PM.
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  #4  
Old 09-29-2010, 11:43 PM
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I just drill two holes in a scrap of 3/8" material when I need circles and arcs. One for a pivot bolt and the other a 3/8" one to fit the tip of the plasma torch. My torch is "live" not a drag style. 3/8" material gives me a near optimum stand off to avoid contacting the work.

I've scorched a lot of 3/8" underlay and OSB scraps making guides and templates. I've got lots left.
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Last edited by camdigger; 09-30-2010 at 08:37 AM.
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  #5  
Old 09-30-2010, 08:16 AM
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Lu47Dan Lu47Dan is offline
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Cam, I make patterns also. I use tempered mansonite for them, but as many circles I have been cutting lately I figure the circle cutter will pay off in the long run.
I am figuring a stand off of 1/4" for now. What I have been pondering is the what to use as a wheel, I thought I had a couple of old wheels for a set of 12" cold cutters but they are not in the drawer with my new ones for my 4" cold cutters. What I am figuring on doing is making a set of wheels for it.
List of parts to be made.
  1. Anchor ring.
  2. Torch ring.
  3. Magnetic anchor block.
  4. The rods.
  5. Bolt on anchor block
  6. And the capture plate for the anchor blocks.
The bolt on anchor block might get made from the centering jig I made yesterday. It is after all a one use device.
Dan.
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  #6  
Old 09-30-2010, 02:21 PM
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Can’t you program the cutter to cut circles?
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  #7  
Old 09-30-2010, 04:14 PM
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Quote:
Originally Posted by kbs2244 View Post
Can’t you program the cutter to cut circles?
Sadly, in my shop, all the torch controls are in the organic peripheral (aka human). The issue does not appear to be in the programming (I know the shape I want), but in the wiring harness or the mechanical drive ( can't hold the torch steady enough to get a smooth cut and can't follow a chalk line worth spit).

A dirt cheap alternative is in the works, but the prototype development (aka reverse engineering) is stuck some where in management's prioitizing of available resources (haven't had time to play with it). It is a shameless copy of existing, obsolete machines. See attached...
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  #8  
Old 09-30-2010, 09:40 PM
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Lu47Dan Lu47Dan is offline
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Quote:
Originally Posted by kbs2244 View Post
Can’t you program the cutter to cut circles?
kbs, my plasma cutter is manual not CNC.
Today I got a few of the pieces made, engineering on the fly kind of slows things down.
  1. Drilling out the anchor ring.
  2. Parting off the anchor ring
  3. Anchor ring and adjusting sleeve.
  4. Adjusting sleeve, jam nut side.
  5. Adjusting sleeve, anchor ring side.
The anchor ring was turned out of a piece of 2-1/4" 1018. It already had a 7/8" hole in it, I enlarged it to 1" and turned the OD down to 2". Then I parted it off to 1" thick, chamfered the hole and test fit it to the centering device. The anchor ring spins freely.
I then made the capture plate for the anchor block, which is 1/2" thick with a 1/2" hole in it.
The adjusting sleeves are made from a 2" long piece of 3/4" hot rolled faced both ends and drilled and tapped to 1/2" -13TPI. I cleaned the mill scale off the one end about a 1/4" wide so I could tig weld them to the anchor ring and the torch ring.
The torch ring is the last of the parts that need made before the welding can begin. I will get that built tomorrow, I need to make a sleeve for my boring bar before i can make the torch ring.
Dan.
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__________________
Tools to Men are like Shoes to Women , you can never have too many !!
Used diesel engines are an adventure anyway you look at them !!
Miller XMT-304 Multiprocess
Miller 10-E Wire Feeder
Miller Spectrum 2050 Plasma Cutter
Hobart AC/DC stick welder
Hobart 175 Mig
Craftsman O/A set
Turbo torch and B-tank
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  #9  
Old 09-30-2010, 10:29 PM
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Hmmm, looks rather familiar.

Steel seems to work ok for the thinner parts. Aluminum is nice, but difficult to keep in one piece when it's thin.
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  #10  
Old 09-30-2010, 10:52 PM
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Sorry, I did not get the big picture of how it's going to work. What my problem is, cutting 1" holes in 1/4 plate with plasma. Yes, I've made one cutter. The only problem is a 3/8" hole has to be cut and maybe a start hole. You can place the torch at any height to start. A complete circle is only changing the height by the width of one thread, that's not a problem for plasma cutting. Other nut sizes can be made for larger holes. Now starting the cut and with all the blow back might be a problem. Maybe you can see why I havent used it yet.

2 cents
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Last edited by Vern2; 09-30-2010 at 11:15 PM.
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