Lathe machining questions

[devinchi]

I don't have any experienced machinists local to me, so I am coming to the pool of knowledge here to get a question answered.

I have some experience with milling, and a little with my lathe. I have basically just done OD work, and facing off the end of a piece.

I have recently come across the need to machine out the center of a soild aluminum bar. Since the bar is circular, and the hole for the center is to be circular I would like to do this on my lathe, but I don't have the right tools.

What tools should I use to produce a 2.45" diam hole in the center of a 3" piece of aluminum round stock? The hole has to go in almost 3".

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[wms]

Devinchi,

You should get as big a drill as you dare.
Say 2.25" (if you have the power and drill chuck for the tail stock to hold it.)

If not get as big a one as you can handle.


Then after you have the hole drilled, you will need a boring bar.
For 3.00 depth you will need at least a .750 diameter bar.
1.00 diameter bar would be better.

Again I don't know what size tool you can mount on your cross slide.

But normally 4 time the bar diameter is all you want hanging out, for steel bars. For heavy metal 6 time is OK. And Carbide bars up to 8 times. I'm talking about the bar material itself, not the insert. It's a stiffness thing and harmonics also.


Make sure that your drilled hole is big enough so you bar can make the first pass. You will see the "min. bore" listed for the bar you choose. Your drilled hole has to be at least that big, plus a little, say .030 more. That way you can move the tool away from the bore to retract the tool.


Then it is just a matter of taking passes with the bar to get it to size. Speed and feed and depth of cut will depend on power, bar over hang, bar diameter, Insert tip radius, (use a .016 or less, IE: almost sharp).

[devinchi]

SO I need to find a boring bar that will work on my toolpost so I can move it offcenter, right?

[wms]

That is correct.

[Bloy2004]

Originally posted by devinchi
SO I need to find a boring bar that will work on my toolpost so I can move it offcenter, right?

Devinchi....
I believe you are talking about the shoptask? In this case the quickchange tool post will be too small. You can mount the boring bar in anything (vise?) that will hold it solidly to the table axis. just have to get it aligned for proper cutter location.

[Swede]

WMS I must disagree with you a bit on the "Giant Drill" recommendation. Drills that size are expensive, require massive horsepower, and are prone to chatter on smaller machines.

I have bored many setups as described using only a 1/2" drill to start. Devinchi, I'd drill to a depth of 2.90", assuming the bore is to be 3.00" deep, you don't want to bore to final depth initially.

Once the 1/2" hole is drilled, open the hole up to about 1" with a smallish boring tool. Then, I'd make use of a 3/4" boring bar, one of the cheap ones which hold a small 1/4" square HSS bit, to do the remainder of the boring. These styles of bars have been around for decades and can take deep feeds in aluminum.

Approaching the final bore, begin to increase the depth of the bore gradually, while also increasing the diameter of the hole. Use smaller outfeeds to remove the spring in the tool, with a final pass (or two) of only .002" or so, this keeps the bore walls parallel and untapered.

Good luck, boring is easy, don't be intimidated.

Swede