Harrison M300 Crash - what fails on the leadscrew?

[Rannsachair]

I foolishly drove my carriage into the carriage stop while screw cutting . Now the Lead screw is not rotating, the feedrod is still rotating.

If I grab the leadscrew it can be freely rotated by hand

Is there a shear pin?

Thanks

 

[Welderpaul]

When i rebuilt my M300 i remember reading in the instructions about a shear pin

 

[Welderpaul]

Page 17 in the manual

 

[Rannsachair]

Page 17 in the manual

View attachment 344596

Thanks, was looking in wrong part of the manual, assumed it was at the lead screw.

 

[Rannsachair]

No luck, knocked the shear pin out and it is intact, anyone any idea what the collars are where the lead screw gows into the gearbox, am hoping it is something there rather than a gearbox strip?

 

[Agroshield]

This is clutching at straws a bit but have you verified that the two parts that are supposed to be joined by the shear pin do turn together when it is inserted? I am wondering if it is possible for it to have slipped out of position and disconnected itself.

Can you confirm that there is input to the gearbox when the spindle turns. Try all gearbox lever positons and confirm they are detented into place. I read something recently about someone knocking his gearbox into a false neutral, which was not obvious from the lever position.

Before stripping the gearbox, it might be easier to undo the bracket at the tailstock end and slide the two shafts out of the gearbox, just to confirm that whatever joins the leadscrew to the gearbox is not broken. That will also enable you to see if the output of the gearbox is turning. The bracket is normally secured by capscrews and then located by threaded dowels, removal of which allows it to move fore and aft without disturbing the apron.

If the feed rod is rotating but the leadscrew is not, trace through the diagrams in the manual and see at which point the drive to the two diverges. That has to be the point of failure. In normal operation do both shafts rotate together?

 

[Rannsachair]

This is clutching at straws a bit but have you verified that the two parts that are supposed to be joined by the shear pin do turn together when it is inserted? I am wondering if it is possible for it to have slipped out of position and disconnected itself.

Can you confirm that there is input to the gearbox when the spindle turns. Try all gearbox lever positons and confirm they are detented into place. I read something recently about someone knocking his gearbox into a false neutral, which was not obvious from the lever position.

Before stripping the gearbox, it might be easier to undo the bracket at the tailstock end and slide the two shafts out of the gearbox, just to confirm that whatever joins the leadscrew to the gearbox is not broken. That will also enable you to see if the output of the gearbox is turning. The bracket is normally secured by capscrews and then located by threaded dowels, removal of which allows it to move fore and aft without disturbing the apron.

If the feed rod is rotating but the leadscrew is not, trace through the diagrams in the manual and see at which point the drive to the two diverges. That has to be the point of failure. In normal operation do both shafts rotate together?

Sorted. the far right bottom selector just needed a wiggle now the leadscrew is driving again, Phew, will be more careful in future, too used to the myford and just getting a slipping belt if I do something stupid.

 

[nickk]

Just like some bikes eh?false neutrals everywhere .

 

[RichardM]

I made a little micro switch housing that slips over the carriage stop and operates the E/Stop system for just such occasions.