On Sat, 14 Jul 2012 20:28:11 -0400, Joseph Gwinn
wrote:

snip

This seems worth exploration.

What do I look for on fleabay to tell if the unit on offer is any good?
Mechanically they are pretty simple, but I doubt that they bounce well.

Joe Gwinn

I usually figure that if they look beat up, they are not worth the
risk if personal inspection is not possible. In general, you need
these components:

1) Bracket
2) TAD base
3) TAD unit (dial)
4) Sphereical washers for 1/4" screws
5) 1/4-28 screws (4)

The bracket is attached to the lathe carriage or mill and is usually
custom-made for the machine it will be mounted on, though SWI used to
(and may still) sell brackets for common machines.

The TAD base mounts to the bracket and has 2 hard inserts that two of
the 1/4-28 screws bear against to adjust the tilt of the base in the
lathe X-Y plane (perpendicular to longitudinal travel). The important
part here is that the inserts should be flat - some are dented.

The TAD unit has the dials and a wheel that bears againts the bed ways
(in the case of a lathe). Swarf from a PO's installation can get
inside the unit, which can mess up the clock action. SWI claims that
the TADs are not serviceable, though some owners report success. I
wouldn't count on it being serviceable so would not pay much for one
that was suspect. SWI included a clip and foam gasket that fit over
the wheel and (mostly) prevented swarf from getting inside the unit,
but these are usually missing. SWI used to supply spares and may
still. The dial cover also was a replacement part and I'd order a
spare if they are still available. Old ones tend to crack and yellow
with age. Naturally you need the dial finger to be intact, too.

A copy of the manual or knowledgeable friend can be nearly essential.
There is a calibration procedure which is a more involved than I care
to deal with in a newsgroup message. Email me if you want a copy. I
get here once a week at most.

There were 2 or 3 different versions over the years. I have manuals
for the Series 6 and Series 7/8 models.

Mike

Hopefully someone else will correct any misinformation in the above.