cutting out 4" circles of 1/8" mild steel plate

I have a need for some 4" circles of 1/8" steel. They have to be pretty flat. They will wind up with a central hole of 5/8". (Tolerance here is about 1/32", not really machinist tolerances.) If I could think of a clever way to hold them by the 5/8" hole really solidly, I might be tempted to try grinding up a trepanning bit - how hard can it be?

I suppose I could try cutting them with a circle template and a plasma cutter, or I could make up a bandsaw circle jig and try cutting them on the bandsaw (don't have a 24tpi blade though) or even borrow someone's hole saw and try banging them out in one go on the mill. I don't have access to a blanking press. I only need 3, so it isn't worth having them laser cut.

I have a few days before I need them. What's the easiest way to cut these?

Grant Erwin Kirkland, Washington

Reply to
Grant Erwin
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How about this approach:

  1. Rough-cut the circles (a bit oversized) with your favorite cutter
  2. Drill a 1/2" hole at the centerpoint of each circle blank
  3. Cut the head off of a 1/2" bolt (with a smooth shank) and chuck it in your lathe
  4. Put a nut on the bolt and run it up tight then put the 3 blanks on and use another nut to clamp them. [Washers optional]
  5. Turn to size
  6. Re-drill center hole to 5/8"

You DID say you wanted EASY, didn't you?

Reply to

... I suppose I could try cutting them with a circle template and a plasma cutter,

I needed a whole pile of similar size a while back. Also needed a tighter spec on size and round. Anyway, I just cut up a bunch of octagons ruff on bandsaw. Drilled center hole. Then took a piece of all thread and bolted a whole stack on the lathe though the spindle center hole. Turn to size.


Reply to
Karl Townsend

Lessee Grant, you have a plasma cutter and a lathe. Rough cut the steel with the plasma cutter. Then put in your 5/8 hole accurately. Then chuck a 5/8 dowell pin in the lathe leaving .350 sticking out. Slide the plates on it. Use a live center to press a plate against your stack of plates that you slid onto the dowell pin. Turn to size. You need a pretty good live center for this. But pressure turning works well and is fast to setup. Take light cuts so the plates don't catch. I used to do a repeat job on an 18" swing lathe where I would stack up 20 each of 1/4 aluminum rough cut plates. These plates did not have through holes in the center. I just pressed them against the chuck jaws with a live center to hold them for turning. ERS

Reply to
Eric R Snow

A plasma torch will cut to that accuracy. Make yourself a washer template and burn the center hole first. If your edge distance on the torch is say half inch your center hole on the template would be 1 5/8 and your outside diameter would be three inches. My first inclination is to hole the template with a magnet but it may give problems with the plasma cut. You also could make yourself up a radius cutting attachment to clamp to your plasma torch much like people use with a oxy acetylene torch. Randy

Reply to
Randy Zimmerman

A jig saw with a good blade will do the job in a few minutes. True up the edges with a grinder after cutting.

Gary Brady Austin, TX

Reply to
Gary Brady

You could use a 4 1/4 hole saw to cut them from flat plate and then enlarge the pilot hole to 5/8- then put a 5/8 bolt and nut through the hole and turn the OD to size

Reply to

I had to make 6 circles recently, 1/8" thick, 6" diameter. They needed to be nice, so I always intended to lathe turn them. Trouble is, when I've done it before using a plasma cutter and a compass-style circle guide, the smallest variation in the angle of the torch head while cutting left the blanks just inaccurate enough to be a pain to turn on my small lathe. So this time I cut them square from 6" wide flat stock, center drilled the squares, and mounted them on my quick and dirty turntable, which was cobbled for a previous project from a modified $10 HF boat winch . Added an adjustable arm to hold the torch head locked in position, and started cranking. It worked so well that I almost could have skipped the lathe turning. You'd think the winch-turntable would need a separate ground to the material, but the current carries through the gear train and bushings without problem. It's overkill for 1/32 accuracy, but you might find it useful for other projects. Very low tech, here's a photo

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Great idea, I like the way you think!

Reply to

Funny, I'm working on a small winch too! I am going to simply remake the drum, but different. Then I'm planning to cut the gear off the original drum and weld it onto this one.

The design is for a table hoist system for an H-frame hydraulic press. I'm modifying the winch to reel cable in and out both sides instead of just one, then I'll mount it in the middle of the top and make pulleys on the top corners and hang the cables from brackets on the outside of the H frame. Hope it works.


Reply to
Grant Erwin

I just made a big specialized washer out of some 3/8 thick material that I had on hand. I needed a 1.5 inch hole, but first drilled a hole

5/8 inch in diameter as I have a mandrel made of some 5/8 rod that is threaded for an inch or so. I just use two nuts and clamp whatever between them. I was not trepanning, but it works well enough to turn the outside.


After getting the outside done, I chucked the disk in the lathe and bored out the inside with a fairly large boring bar.

Grant Erwin wrote: If I could think of a clever way to hold them

Reply to

Yep! Works just fine. I've used that system for so many years I've lost track.


Reply to
Harold and Susan Vordos

How about a hole saw?? in a drill press? cheap tool a good one would do the job just fine wouldnt it?


Reply to
Doug Schultz

I'd be surprised to find a home shop type drill press that could run slow enough to run a hole saw that size in steel.


Reply to
Harold and Susan Vordos

Al cuts so nice with a plasma - vaporizes and powers the metal and it cuts. I tried a small item on my CNC plasma - nice sharp edges. Martin

Reply to
lionslair at consolidated dot

Yep, Harold. Me too! Most folks don't view the hole saw as a machine tool - one that has a specific range of speed and feed. The same with trepanning-type circle "cutters". And reamers - aren't they all the same as that tapered, sheet metal reamer Granpa used to use? I think the term "cutter" is what sucks us in. If it says "cutter" anywhere on the label, it must be easy and safe to use as scissors and other cutters we grew up with.

Bob (Please don't take me back to the old days) Swinney

Reply to
Robert Swinney

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