Is it normal for half-nuts on older lathes to "hang up" or not smoothly
engage the leadscrew with each and every close of the half-nut lever?
Not being the original purchaser of this lathe, I do not know how it
behaved when new from the works (around 1970). The lead screw is 1-1/2"
x 8 tpi.

The half-nut hangs up say 50% of the time. A small movement of the hand
wheel fixes the problem by shifting the carriage slightly. I've taken up
using the thread dial to guide the timing of the closing of the
half-nuts, but even this dodge does not provide a smooth close 100% of
the time. Sometimes the half-nut grabs on the outside of the leadscrew
(land?). At other times, it does not appear to want to close more than
half of the normal distance.

The leadscrew has been cleaned of all chips, swarf, compacted dirt etc.
The half- nuts have been removed and similarly cleaned. The half-nuts
close cleanly on the leadscrew when they are off of the lathe. Wear does
not "appear" to be excessive. The OD of the leadscrew is the same at the
ends of the screw and in the middle (no wear?).

If this behavior is not normal, what can be adjusted or where should I
look to find the problem?

Thank you in advance for any insight you can provide.


-- 
PointFive
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"PointFive"  wrote in message 
news:PointFive.3epron@rcgroups.com...
>
> Is it normal for half-nuts on older lathes to "hang up" or not smoothly
> engage the leadscrew with each and every close of the half-nut lever?
> Not being the original purchaser of this lathe, I do not know how it
> behaved when new from the works (around 1970). The lead screw is 1-1/2"
> x 8 tpi.
>
> The half-nut hangs up say 50% of the time. A small movement of the hand
> wheel fixes the problem by shifting the carriage slightly. I've taken up
> using the thread dial to guide the timing of the closing of the
> half-nuts, but even this dodge does not provide a smooth close 100% of
> the time. Sometimes the half-nut grabs on the outside of the leadscrew
> (land?). At other times, it does not appear to want to close more than
> half of the normal distance.
>
> The leadscrew has been cleaned of all chips, swarf, compacted dirt etc.
> The half- nuts have been removed and similarly cleaned. The half-nuts
> close cleanly on the leadscrew when they are off of the lathe. Wear does
> not "appear" to be excessive. The OD of the leadscrew is the same at the
> ends of the screw and in the middle (no wear?).
>
> If this behavior is not normal, what can be adjusted or where should I
> look to find the problem?
>
> Thank you in advance for any insight you can provide.
>
>
> -- 
> PointFive
> ------------------------------------------------------------------------
> PointFive's Profile: http://www.rcgroups.com/forums/member.php?u=225133
> View this thread: http://www.rcgroups.com/forums/showthread.php?t=914362
>
It seems to me that what you describe is normal operation. The half-nuts 
cannot fully close unless they are in alignment with the thread on the lead 
screw. Unless you have a lot of backlash, careful attention to the thread 
dial should permit closing at the proper time/position. The thread dial may 
need some adjustment if it is not indicating properly.

Don Young (USA)