On Wed, 7 May 2008 20:08:15 -0700 (PDT), wrote:

I have an aluminum tube that I need to bore about 1" at end out to at
least 5.57" -- it varies from about 5.47" to about 5.60".
Unfortunately, this is too big to put on my Sherline lathe--it won't
fit onto the outside of chuck that I can find for the Sherline. I
have this vague notion that there might be some way to do this by
putting an end mill in the headstock and rotating the workpiece so
that the end mill removes a fairly consistent layer. This doesn't
have to be spectacularly precise. I tried this approach, and except
that I couldn't figure out a way to get the workpiece to turn
consistently (since it wasn't supported), it almost seemed to work.

Does anyone have any clever ways to do what I am trying to do, without
breaking down and buying a bigger lathe? Some clever way to mount the
tube on a 3.5" OD chuck, for example?


Depends what other facilities you have. Since the tube is larger than the
swing of the lathe you are going to have to make the lathe bigger.

Buy a 2" boring head and turn up an adaptor to fit it to the mandrel nose of
the Shereline. This is going to be a bit heavy for the lathe to hold but it
should manage and can be adapted to fit other lathes or mills you might get in
the future.

Remove the tailstock.

Get a piece of 1.5" to 2" thick aluminium cut and drilled to size to make a
rising block to lift the headstock up to cope with the diameter of the pipe.

Get another large piece of aluminium to clamp onto the cross slide. Drill for
clamps, rough cut a radius in one edge with bandsaw, chain drilling, whatever.

Lock the cross slide gibs (don't want them moving 'till the end of the job).
Clamp the aluminium block to the cross slide

Use the boring head to cut a the radiused edge to the radius of the outside of
the tube.

You now have a work holder on the cross slide that will hold the tube
accurately on centre. Use your third hand/a friend/roller skate/pet cat to
steady the far end of the tube. Use the boring head to bore the tube to the
right diameter.

You'll probably need to use a sharp HSS bit in the boring head and take small
cuts throughout even with aluminium, due to the large diameter you are
cutting.

This may be more precise than you want, it is also a lot of work. But it will
give the result.


You did ask :-)


Mark Rand
RTFM