How to cut a 3.125" dia half circle in 6" long aluminum?

GregSY · Oct 20, 2018

Water jet? EDM?

I want to end up with a 3.125" half circle cut out of a bar of aluminum. The bar is 6" long, and 5"x5" square when viewed on end.

If I had a big drill bit, I could chuck up the bar in the lathe and just drill a hole, then cut the bar in half longitudinally. I guess I could start with a smaller hole and use a boring bar but that's a lot of turning.

The exact diameter of the hole is not super critical (+/- .15") but it needs to fairly straight...a taper would be bad.

john.k · Oct 20, 2018

You gave your own answer.....do it in a lathe.....1" pilot hole,cut out 1/2" per pass(1/4 cut) ,done in 5 passes...whats difficult about that?.........

CalG · Oct 20, 2018

A fly cutter on a mill would have that job done more quickly that you can read this forum.

Get at it!

Hazzert · Oct 20, 2018

Boring head. Find centre in Y, find your edge in X. Move over 1.5625”. Set a boring head until it just scratches the face and step it in until you get back to your zero. Your machine and boring head will dictate how long that takes.

johnoder · Oct 20, 2018

Cut in half (still have the 36" Crescent?)
Rough out on same machine - narrow blade with coarse pitch
Mill joint
Put halves in lathe, hold with four jaw and bore out. Use front clamps as needed (like if the four jaw is a wimp)

CarbideBob · Oct 20, 2018

An edm or waterjet sounds like a not great idea.
What machines do you have?
Part is 5 inches thick (or deep) from our profile view or 6 inches? (just a mention as the front view looks easy)
Sort of a 1/2 boring job and square, true and no taper is important?

On say just a B-port I'd probably drill a bunch of holes around the circle, knock out the slug and then get out the boring head.
Even on a cnc mill I'd do likewise.
Turning and boring is faster cutting than drilling or milling but a whole lot of material is made into little chips needlessly.
Bob

eKretz · Oct 20, 2018

It sounds like he wants to send this out and have someone else do it. If that's the case, EDM should be the easiest and it should be fairly straight if they know what they're doing. If you're going to do this in house it will depend on available machinery. If I had to do it, I'd go with an hbm. Set it up and punch it out with a boring bar just like described by Hazzert. I guess I'd have that done in less than half an hour.

Mr. Haney · Oct 20, 2018

I think they cover this in Machining 101 at the local college.

Dan from Oakland · Oct 20, 2018

right angle head on a Bridgeport with a flycutter. Cherrying attachment on a Bridgeport- that's exactly what they were made for!. What John said. Vertically on a Bridgeport. That's the manual side- lots more CNC options.

john.k · Oct 20, 2018

Seems like a strange question from someone with 5,250 odd forum posts..

Finegrain · Oct 21, 2018

For just 1 I would 3D surface it in my CNC mill with a 3/4” ball endmill. Rough out as needed first.

Regards.

Mike

Limy Sami · Oct 21, 2018

Lathe job ;- as in keep it simple

number 2 · Oct 21, 2018

Clamp it to the lathe cross slide with center of radius longitudinal. Make a bar with cutter and line bore it with successive cuts applied with the cross slide.

Gordon B. Clarke · Oct 21, 2018

john.k said:
Seems like a strange question from someone with 5,250 odd forum posts..

That did cross my mind too. It is after all "only" aluminium. A drilling machine and a 3 1/8" or an 80mm (3.15") drill and then cut in two.

GregSY · Oct 21, 2018

Thanks for the good comments. I kinda figured using the lathe would be my best choice but wanted to make sure I wasn't missing the best combination of time/cost/effort.

As for the few stupid-ass comments, well, that's why you're stupid-asses. You don't know enough to ask for other ideas before you start.

Lewie · Oct 21, 2018

I did a similar thing in 1-1/2 or 2 inch steel about 3 years ago by chain drilling, bandsawing, and boring.

...lewie...

ostie01 · Oct 21, 2018

GregSY said:
Thanks for the good comments. I kinda figured using the lathe would be my best choice but wanted to make sure I wasn't missing the best combination of time/cost/effort.

As for the few stupid-ass comments, well, that's why you're stupid-asses. You don't know enough to ask for other ideas before you start.

And remember, you must do it in 30 minutes or less or, you will have to unsubscribe from this forum.

EPAIII · Oct 21, 2018

I have thousands of posts here and on other sites. But that does not make me an expert. It only means that I have been here a long time. I am sure some of my posts were not helpful. What not to do is also good to know. I learned from them and I hope others also did.

john.k said:
Seems like a strange question from someone with 5,250 odd forum posts..

kazlx · Oct 21, 2018

It also depends on if you want both halves usable or the same size. You will lose your kerf size on whatever you cut it in half with. It really does make a difference if you want the 'best' way for the equipment you have on hand and want to do yourself, or if you are sending it out. EDM would be pretty much perfect, but also by far the most expensive. All the other methods will work. Personally, I'd probably either just turn it to chips and surface in the cnc or chain drill and saw it out and then surface it. Probably the first since it's way easier to click a few more buttons and have the cnc hog it out.

GregSY · Oct 21, 2018

Lewie, that looks really good. I'd be concerned with keeping my bore parallel to the bottom of the workpiece, which is pretty important, going down a 6" travel.

I only need half of the circle so kerf doesn't matter. Anyway, good ideas so now I need to order material...

How to cut a 3.125" dia half circle in 6" long aluminum?

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