Circle Milling

[asallwey]

I was asked to cut a few circles from 1/8" aluminum plate, no center hole. It didn't go so well, so now I'm trying to figure out a solution.

#1. What's a good way to do this?
#2. What might I be doing wrong, or what should I change in the procedure below.

I'm using a 4" boring head with a 1" horizontal bar and a 3/8" square tool. As you can see in a photo, the tool extends out from a side bottom hole. A 3" head would probably be better, but this is what I have. The center locking screw is against a flat, the other locking screw is on the curved body. The mill is a Millrite, and it's set at the slowest speed, 250 rpm. The table is locked and the knee is tightened between raising the table. I ground the tool and it's very close to how I grind cut-off tools.

I'm getting both chatter and squealing all the way around. Depth of cut is probably 0.0005" as I'm taking 2 "bumps" on the knee to move 0.001" on the dial. I would normally use a higher speed for aluminum, but with this mass I'm chicken to turn it up. The practice plate I'm cutting is held by a bolt head in the vice and has 2 hold down clamps in line with the vice (one is visible in a picture). I'm not trying to cut all the way through, just make a groove.

Thanks,

Alex

[GlennW]

If you only have a mill to work with, I'd clamp it down to to a sheet of plywood so it wouldn't resonate so much, and use coolant/lube.

Do you have the proper relief ground on the outside surface of the cutter so that it doesn't drag on the aluminum?

I'd use a lathe and rough cut them using a band saw and then push them against the chuck jaws with a disc of wood using the tailstock live center and turn them to the finished diameter.

[pete]

Good industrial grade double sided tape and not something like Home Despot sells as carpet tape will help fix the piece that's getting cut out in place. If it can move after it's cut free of the plate your almost sure to have a crash.Work and whatever backing piece your using has to be very clean and the work sort of burnished down so the tape will grab properly needs to be done as well as you can. Google trepanning, read the explanation then hit the image tab and you should find examples of the correct cutting tip shape. But trepanning is the correct term for what your trying to do. The cutting tool needs relief on both the outside and inside so it's not trying to rub on the work. Sometimes a hook shape just behind the cutting edge helps to curl up the chips. It's just a cut off tool with the tool spinning instead of the work like cutting off in a lathe. Since it's aluminum I'd try ample WD 40 as a cutting lube as well.

[SteveHGraham]

I think Glenn has identified the problem. You are pretty much guaranteed to get friction on the outside of a straight tool cutting in a circle.

I assume you don't have a rotary table. An end mill and rotary table would do this job in a hurry.

[asallwey]

Glen, I do have a lathe, but the original piece was a rectangle that I was to get several pieces from. I could rough cut them on my bandsaw, but then I couldn't think of a way to make them round.

Your comment about side relief - hmmm, I need to check, I might not have it. The idea of a wood base would reduce vibration, have to try it.

Pete, I forgot about the double-sided tape, have to pick some up.

Thanks guys, I've got some more things to try, good thing it's the weekend!

[BadDog]

I've done what you are trying to do using a trepan tool, much less rigid than your boring head. It's was no fun, but with the tool properly ground it's much better than you describe. The key is it must have clearance. If anything behind the cutting edge rubs, it's a miserable process.

[wlw-19958]

Hi There,

What about "plating?"

Good Luck!
-Blue Chips-
Webb

[Harold_V]

What about "plating?"

That's already been suggested (by Glenn)
"I'd use a lathe and rough cut them using a band saw and then push them against the chuck jaws with a disc of wood using the tailstock live center and turn them to the finished diameter."
I couldn't agree more. I've done a huge amount of turning that way, and with very good success.

Many years ago I had to trepan a large number of washers (about 3" diameter, 1/8" thick) from stainless, for use in a gasketed filter press I built for my refining service. The filter press was used to separate silver and gold laden cyanide solution from finely crushed ore. I used a boring head to create the blanks, which were then finish machined on the perimeter (pressing with the tailstock), so they could be held in soft jaws for facing and boring. The trepanning operation was quite difficult, although the bulk of my problems went away when I switched to Boelube, which required I make the purchase, along with the mist dispenser. I had tried a large variety of lubricants prior to the purchase, none successfully (broke several tools), so it was the right thing to do.

Harold

[earlgo]

If your stock is rectangular then I would bolt the stock (through the corners) to a wood backer like a similarly shaped piece of plywood, clamp it in a 4 jaw chuck, and trepan the part out on a lathe. As has been mentioned, if the part is cut through, the last parting may cause a crash. By pushing on the center with a tailstock pad during the last few thousandths of the cut will help prevent that. As was also mentioned, the cutter relief should not be straight, but curved to sort of match the outside curvature being cut.
I've done this many times making odd sized washers, especially from very thin shim stock. In this case one cuts out the center then the OD with little concern for crashing.
--earlgo

[WesHowe]

While it is mainly done on a lathe, not a mill, you might want to watch Joe Pie's Youtube video on making aluminum washers 0.006" thick. I think it is relevant to your problem.

https://www.youtube.com/watch?v=lGsA_q4guwM

- Wes

[John Hasler]

Rough out the disks on the bandsaw, stack them between wood disks with double-sided tape, grip one wood disk with the chuck, put pressure on the other with the live center, and turn the whole assembly to diameter. The thickness of the stack of disks has to be much smaller than the diameter and don't take deep cuts.

[RSG]

I can't believe no one has suggested soft jaws! If the material is rectangular chuck it in a four jaw chuck and turn to the correct dia then part off oversized. Turn up some soft jaws and finish the back side in them. I do it all the time with soft jaws and have been successful as thin as .04" thickness.