Re: Aligning the tailstock?

On Thu, 1 Nov 2007 16:01:04 -0500, DR_G <DR_G.2ze2kn@xxxxxxxxxxxx> wrote:


Hello again,

Basic question no 537 from me:

I'm about to start my first 'real' machining job. It is basically
drilling out a 120mm long, 12mm o.d. bar to 8mm i.d., and relieving the
ends slightly to take 10mm o.d. ball races. The ball races support a 6mm
dia solid shaft (coaxial with the first) with a 'chuck' at one end and
an internal square drive socket for a flexible drive shaft at the
other. The 'chuck' is really a conical bit at the end of the inner
shaft, drilled and tapped to 1/4-28 UNF 2A to take threaded shank twist
drills. For this inner shaft/chuck I intend to turn down another piece
of solid bar to 6mm o.d., leaving a 12mm diameter by about 50mm long
conical end bit for the chuck (thus making the chuck and outer shaft
the same diameter for neatness). I am going to mill a couple of flats
on the chuck in order to fit a spanner for tightening the drills.

My questions are:

1) Any general advice as to how to go about this?

2) What is the best way of aligning the tailstock with the headstock? I
ask this since turning the inner shaft down from 12mm to 6mm diameter I
intend to do between centres, and this needs to be accurate because it
will have a bearing at each end of it. It may be best to turn the
central portion of the inner shaft down a bit (between the bearing
'lands') in order that I can get the first bearing all the way upto the
'chuck' without forcing it all the way along a tightly fitting
(hopefully!) machined surface.

Material is Austenitic st. st. Ground bar, 12mm o.d. x 300 long
initially, for both shafts.

Cheers,

Garth.


In the absence of a gun drill, start with 15mm bar. Clamp one end in the chuck
and the other in a properly aligned fixed steady. Face the end off and use a
spotting drill, or centre drill if that's what you've got, to start the hole.
Drill the hole with a new, long, split point drill

http://www.jlindustrial.co.uk/ part No HSS-66087C, for instance.

use plenty of cutting oil in the hole and withdraw the drill often to clear
the flutes and lubricate the hole.

Once you've done that, mount the "tube" between centres and turn it to the
final diameter. This will ensure that the hole is central. Then counter bore
for the bearings.

With a gun drill, the operation becomes a lot easier.


Mark Rand
RTFM
.

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