i have a 10"logan lathe and now that i'm starting to do threading a lot
more, i've run into an issue with my compund. when i adjust the
indicator dial and lock it down, and then back the coumpound away from
the spindle, everything is fine, the indicator turns correctly, and life
is good. However, whan i advance the compund towards the spindle, the
indicator seems to bind up against the face of the compound and it stays
in place while i turn the handle. not good if your trying to advance a
few thou at a time for threading as you lose all reference. I've
disassembled, cleaned, lubed, etc, but i can't seem to figure out why
it's binding like this.
joel joel email@example.com
If it's like an SB:
You don't want to "lock" the micrometer dial in and then back the compound
slide out. That puts you back into backlash (the play in the screw and nut
between in and out).
Back out both the cross slide and the compound slide.
Start the compound slide back in a half turn or so to eliminate backlash there.
Run the cross slide back in to just "touch" the work (while the lathe is
running). This eliminates backlash on the cross, and gets you to your starting
point for threading.
Stop the lathe, and set (lock) both mic dials to their zero. Make sure that
the handle does not move whatsoever when unscrewing and repositioning each mic
dial to the zero.
Run a pass on the work to see that you have set up the correct tpi you want to
cut--the touch depth will give you a scratch thread.
Run the cross out beyond the zero for the trip back to the starting point, then
bring it back to its zero to start again. Infeed with the compound. Never
back the compound out during the entire course of threading.
The backlash you put back into the cross with each pass doesn't matter.
OK, this is a pretty common problem. By 'indicator' here I figure
you are actually talking about the graduated dial that gives you
the number readings.
So what's going on is, to repeat your comments above, is that
the handle and dial turn together as a unit when backing out,
but the dial 'stays behind' when you turning the handle forward.
If that's the general effect then the problem is pretty simple,
you don't have enough axial clearance on the crossfeed screw shaft
for the handle to freewheel.
Typically the thrust force on the shaft is taken by two surfaces,
when there is no actual thrust bearings on the shaft. One surface
is the inner lip of the screw which bears on the inside of the
bushing that threads into the apron (this is a typical SB
construction btw) and the other surface is often the inside of
the graduated dial which is backed up by a nut, eventually,
on the outside of the shaft. The handle is in between these two but
is pretty much allowed to float axially.
So it's possible that the entire stack is set up with too little
clearance so that when you are dialing the handle in, the surface
that's taking the thrust is the dial against the bushing surface.
If there's too little slack there to start with oil can't get in
there so it will hang. Or if there's any wobble or unevenness
in the shaft it will cause the dial to be tight locally on the
bushing face and it will bind in an uneven fashion.
So you might look at the stack again in that light.
If there are true thrust bearings in the stack then the
answer is even more simple, in that case the dial has to be
free to float at all times (it's not being used as one of
the thrust elements then) and you need to thin it down
Also be sure that the brass or copper slug that's supposed
to go under the clamp screw for the dial is actually present.
Those get lost over time. Easy to fabricate.