Large sheet metal circles

[L Webb]

That's OK Albert. Most people don't know what roto-blanking is. It is similar to rotary shearing. However, the machine is far superior to those wimpy circle shears.
There is also only one machine in existence. We can cut 1/8 and 3/16 circles up to 39" on it all day long, and fast.
We can also trepan with the same machine.
Les

Sorry Les. There are so many Rotozip like tools that are called Roto<something> that I thought that you were referring to these tools generically as Roto-blank. I guesss my ignorance is beginning to show.

Albert


[This message has been edited by Rotate (edited 05-08-2003).]

[yf]

Yeah.

Cutting discs with the chopsaw makes a very true circle. Very noisy dirty etc.
I also have torch circle cutting attachments.
The circles they produce does not come close to what the chopsaw did. It is basically like cylindrical grinding. Remember, I roughed out with the cutting blade and finished to size with the grinding wheel.

Poor boys cylindrical grinder

[Cass]

yf,
The use of a chop saw to cut circles is a great idea. I can imagine that making a pretty round disk with a pretty nice edge. Probably a noisy, dirty job but effective and a cleaner edge than using a torch. I have cut nice circles with an acetylene torch equipped with a circle cutting attachment that you can buy at a welding supply shop. It is a steel rod with a ring and set screw on one end to hole the torch and an adjustable point on the other end to fit in a punch mark or hole on the other end. With what is referred to as a "drag tip" on your torch you can cut nice circles. The drag tip has the pre-heat holes in a a straight line and it has a small wheel to allow the tip to ride on the material being cut. Works well on mild steel plate with practice.

With regard to jig sawing thin metal l would sandwich it between plywood. Cuts down the noise and vibration, guides the jigsaw blade and makes a cut with less of a burr. Use some spots of spray glue to hold the plywood to the sheet metal. Notice I said "spots" not the whole surface or you will have a lot of trouble getting the stack apart.

[Dr. Rob]

Okay...one BIG holesaw. Run at low RPM, like, one.

[yf]

I cut a 24" circle out of .25" steel plate with a chopsaw.

First drilled center hole, then drove lag bolt through hole into piece of oak 4x4 about 3' long, clamped 4x4 in chop saw vise so blade was cutting a bit over sized.
Then locked switch on and with gloved hands fed the plate around and around till cut through. As the blade wears and gets smaller it is able to cut deeper in the plate. Then removed blade and replaced with 9" angle grinder wheel and moved the 4x4 in slightly and then ground edge to square up edge all around.
Time consuming but faster than torch cutting and cleaning up.

Now I have a 12 gauge powered beverly shear.
Still wont cut .25" plate.

[This message has been edited by yf (edited 05-07-2003).]

[Thrud]

audrey:
I assume you want a nice job of it...

You can do it two easy ways, the first involves a metal cuttin vertical bandsaw with an out arm attached with a pivot point at the radius from the blade. You turn the 14Ga. into the blade and you willend up with a perfect circle with a small (1/4" is good) hole in the center.

The other way is with a nibbler - again, attach a stiff arm to it so it can pivot and make a smooth cut.

Other ways that can be done is cutting with a sawzall {regular jigsaws are too light for this), plasma torch, gas torch, CNC Turret punch, Laser, and water jet.

[CCWKen]

I've never seen a Roto Press that can handle 14ga. steel. But I guess if you can cold roll it, you could blank it too. I would think tooling up could be costly though.

[L Webb]

Rotozip?????? I think you'd go deaf and dumb trying that.
I said I'd roto-blank them.
Les

RotoZip on 14 gauge steel? I'd like to see that done. What bit did you have in mind.

Albert

[L Webb]

I would roto-blank them. It would take less than a minute to cut both.
Trepanning would work also, but take a little longer.
No centerhole required either way.
Les

[CCWKen]

You didn't say if it was ok to have a hole in the middle or what kind of tools you have to work with. Most of the above will work in a pinch. If you'll be doing this a lot, I think I'd make a radius jig for a band saw or SM rolling slitter. (I have both--I hate to waste good plywood cutting circles)
If all you have is a jig saw, then I agree with just drawing and cutting. It's going to want to wander.
Forgot to mention-- That's going to be one heck of a Bar-B-Que pit! 26" ends!



[This message has been edited by CCWKen (edited 05-06-2003).]

[darryl]

I should have added in my reply that a lot depends on the shape of the jigsaw. If it's sloppy, I'll agree with Dr Rob, just go at it by hand, and you'll make the blade follow the line by sight. If it's in good shape, which most aren't, by the way, you can use a circle jig happily.

[SGW]

How good an edge and how close to round do you need?

[gunsmith]

A simple and quiet way to cut thin sheet metal is to sandwitch it between two pieces of scrap plywood or MDF type material. I prefer 1/2 inch and in most cases the plywood does not go to waste afterword. There are always uses for 14" circles or 6" circles or . If I am using my jig saw there is a slot in it for a pivot bar. If not use a mounting screw drilled into the plate of the saw to which you can attatch a bar to act as a pivot point. This method helps the blade run true and on most jig saws a wondering blade is the norm. By the way, use a corse cuting blade or you will smoke out the shop. Good luck!