Boring from the tailstock

[T70MkIII]

Gentlemen, I'm about to spring for a MT3 arbor and boring head set from CTC Tools for my X2 mini mill. For just a little bit extra I can also pick up an MT2 arbor, so I could potentially use the boring head in the tailstock of my C2 mini lathe.

That said, is there any reason, other than rigidity or possibly the length of the job, why one would bore from the tailstock rather than mounting the boring tool on the toolpost?

Forgive me if I have answered my own question here - it's just that I've seen lots of threads showing pictures of the latter setup, suggesting it works just fine. Perhaps it's the C2's wobbly toolpost (I haven't yet removed the compound or made new gibs) that has me worried.

 

[Brian Rupnow]

One of the things that immediately comes to mind, is that when the boring head is mounted in the tailstock, you have to reach a long way out, across the compound rest to get to the workpeice in the chuck. The farther you have to reach, the less stability you have. Also, when the boring tool is mounted in the normal toolholder, you can use your crossfeed to back the tool up towards you into the cut, and the large dial on the crossfeed is a heck of a lot easier to read accurately than the microscopic one on a boring head. The only advantage I have seen in mounting the boring tool in the tailstock, is that if you put a center in it instead of a boring tool. it lets you do offset, between centers taper turning.

 

[GWRdriver]

I kind of feel like a broken record on a few issues, but here I go . . . I'm not saying it won't work or that it won't do some curious little job, but if it was such a good idea everyone everywhere would be using it and it would appear everywhere in machining instructions and descriptions . . . but it doesn't . . . anywhere, so it must not be such a good idea. The reason is, the further away from the central axis of the structural spine of the machine (bed, headstock/spindle bearings) you place the cutting edge the more moment is created and therefore the less rigidity (and accuracy) you have. A tailstock boring head would place the cutting edge about as far removed from the basic structure as you can get ( aside from a 3ft long boring bar) and a great deal of rigidity would be lost simply because the tailstock ram needs to be free to move. .001" of clearance in the ram translates into several .001" radially at the end of the tool tip, in addition to whatever deflection takes place in the boring head and bit assembly. I'd save my money.

Addendum - Brian's post got in while I was writing and we are essentially saying the same thing.

 

[tel]

I do it from time to time, but as hHarry and Brian say, there are more drawbacks than advantages, not least of which is the loss of power feed.

 

[T70MkIII]

Thanks very much - I appreciate your input and experience.

 

[jpeter]

Seemed like a good idea to me too but I gave up when the taper kept falling out.