Boring al tube for a spider

I bought some 3" aluminum tube to make a spider for my lathe. The od of the spindle is about 2.05 and the id of the tube is 2.0. I'll have to take .05 of the id of the tube for a slip fit on the spindle. Now my confession of ignorance, I have never used a boring bar. I have boring bars and holders for both my lathe and mill but have never used them. Any recommendations on which machine would be best to do the job? Also a very basic question, which direction is best to do the cut, outside in or inside out? I bought a 12" piece of tube so I could cut off a short piece to practice on before doing the real thing.

Here ya go

Do you have a steadyrest?
Set up your piece of material in a 3 jaw and the steady. Leave enough outside the steady so you can part the finished work off to length. Indicate the tube. Face the end, bore to desired diameter and part off. Before you part off you might think of a way to catch the piece that will drop. Maybe run the tailstock up in the tube a ways.

No steadyrest?
Indicate the part as well as you can in the chuck, part off to length near the chuck, (your new spider is in the chuck and the bigger piece you cut off is going to fall so think about how to catch it) flip the piece end for end, figure out spacer to let you bore the piece in the chuck without hitting the chuck face, face the second end, bore the I.D. A piece of wood the right shape to stay in the jaws might be a good spacer. Gently touching the wood with the boring bar won't break anything and lets you know you're through the bore. You might get by without a spacer just leaving a gap and you might bore your chuck that way.

adamsgt said:

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I have boring bars and holders for both my lathe and mill but have never used them. Any recommendations on which machine would be best to do the job? Also a very basic question, which direction is best to do the cut, outside in or inside out? ....

Click to expand...

Lathe, absolutely positively; it's easiest to start the cut at the mouth of the bore so you can do a short section and establish your finished bore diameter.

Then rough out the bore, safe in the knowledge that if the tip doesn't touch the short witness bore, you're not out to size yet.

When ready to take a finish cut, use a diamond hone to freshen up the cutting edge and radius, and (with the lathe stopped) touch off on the witness bore, zero the dial, then back off past the backlash, run the spindle up to speed, and come in (actually outwards on the cross feed) carefully as you approach zero to make sure you only kiss the witness.

You'll want to be running at top speed, and using kerosene for the finish cut.

Another factor: If you're using a tipped boring bar, it's designed for cutting inwards rather than outwards.

BUT

The one thing to watch when cutting inwards is to make sure you don't bore into your chuck
or spindle taper bore


If you have a carriage stop, this is a good time to use it.
A small toolmakers clamp, or a mark on the bed, or some other such, is a good idea.

Just make sure you re-establish it if you make any adjustments to the boring bar or the compound slide.

EDIT:
Henrya posted while I was pondering - good stuff, esp. wooden spacer (although it will trap the swarf at the end of the hole somewhat ...

A steady rest is a good way to avoid squashing the tube out of round if it's thin walled, and provided you have enough spare length. Also if the hole in the chuck is not big enough and the job is quite long.

(6 Jaw chucks are best but mucho dinero; a 4 jaw may be worthwhile as the squashing tendency is somewhat less and the hole is usually bigger)

However: you do have to watch it when using a steady rest on aluminium. It either needs to be a roller steady (preferably plastic rollers) or you need to wrap a strip of good quality card, well oiled, around the work inside the jaws of the steady, trapped in the nip of the clamp. Some people use thin leather - I find card works best though if you want minimal polishing effect...

Wow

Thanks so much guys. Just the kind of help and advice I needed.