Lead Screw not turning consistently

[LTRDavid]

While threading a barrel tenon my L

eadscrew quit turning. Fortunately I pulled out before damaging the threads beyond the point of being able to clean them up. One observation is this happens only in US Threads setting. In the metric thread setting the Leadscrew works fine. It appears the shear pin is still intact as the coupler and leadscrew turn together. I am trying to gather information before before I drain the QC Box and pull the cover off, so any comments would be appreciate.
Thanks

 

[macardoso]

It looks like the clutch or engagement lever to switch between threading and feeding is loose, worn, or damaged.

 

[Jim F]

I would be looking at the shear pins.

 

[LTRDavid]

Yes, I think you are correct, @macardoso. Thanks for your quick reply. I spoke with Mike at PM earlier and we are all three in consensus as to where the problem resides. He was very helpful with what information I could share. Plus, I learned the front cover can be removed without removing the knobs! Next step, drain the QC gear box. I’ll take pics to share with the next guy here who may have this issue. Thanks agai.

 

[brino]

@LTRDavid ,

Welcome to the group!

-brino

 

[JimDawson]

Looks like the lead screw/feed selector is bouncing between feed and lead screw. Maybe make sure it's firmly engaged one way or the other.

 

[Ulma Doctor]

generally,
either the leadscrew OR the apron drive shaft will turn at a time.
if they are both turning, that may indicate a shear pin has been sheared and providing friction (enough to drive the opposing shaft)
a worn shifting fork may also prevent a sliding gear from completely disengaging drive.

i'll be following to see what the actual problem(s) are

 

[Jim F]

generally,
either the leadscrew OR the apron drive shaft will turn at a time.
if they are both turning, that may indicate a shear pin has been sheared and providing friction (enough to drive the opposing shaft)
a worn shifting fork may also prevent a sliding gear from completely disengaging drive.

i'll be following to see what the actual problem(s) are

Just the way the leadscrew is turning tells me shear pin.

 

[jbolt]

Just the way the leadscrew is turning tells me shear pin.

I believe the OP has a PM1440GS which has a selector knob for inch or metric threads and says it works fine in the metric position which would rule out the shear pin.

 

[LTRDavid]

Follow-up; drained the oil, carefully removed the front cover after making a picture of the knob settings. Next performed was a general check for any obvious problems, e.g. broken shear pin(s), wear marks, etc. and nothing was determined. With the obvious ruled out, an attempt was made to re-create the symptom. During this process it seemed holding left-to-right pressure on the cam the leadscrew turned consistently. This made me wonder if the interface between gears 112 & 141 were not meshing properly. So, I replaced the cover to test this and sure enough the lead screw now turned consistently. I wish I could be more specific about a solution, but that’s the facts as best I can relay them. Here’s a short video of holding pressure on the cam And a pic of the two gears 112 & 141.
Thanks to all who responded.