Grafting feedscrew (Q from a new guy)

[EdK]

(04-28-2015, 11:30 AM)TomG Wrote: I'm a little late to the party, but it still seems like a good time to throw a monkey wrench into the whole shebang.

Most lead screws have a joint with a slip fit that are then pinned with a soft pin that will shear if some idiot runs the carriage into the headstock. If that happens, the pin will shear off rather than teeth on a drive gear. All of the aforementioned techniques will make a secure joint, but if you want some insurance, I would suggest pinning it instead.

Tom

I wish my lathe had a shear pin. I've often thought of trying to add one but I'm not sure the lead screw in its current configuration can accommodate one.  

Ed

[DaveH]

(04-28-2015, 11:58 AM)EdK Wrote: I wish my lathe had a shear pin. I've often thought of trying to add one but I'm not sure the lead screw in its current configuration can accommodate one.  

Ed

It probably has - you just haven't found it .......... yet
My lead screw is pinned.
So my opinion is the same as Tom's  'pin it'   - no heat, no loctite.   .............. probably an age thing

DaveH

[EdK]

(04-28-2015, 02:02 PM)DaveH Wrote: It probably has - you just haven't found it .......... yet
My lead screw is pinned.
...
DaveH

I guess I misspoke. My lead screw is pinned but not with a shear pin. It's pinned with a 3/16" spring pin with a breaking strength of about 4100lbs.

Ed

[Vinny]

That's so your gears will protect the pin.

[Mayhem]

(04-28-2015, 11:58 AM)EdK Wrote: I wish my lathe had a shear pin...

Attention and a fear of crashing my lathe is my shear pin

[TomG]

I think that makes you a shear pin Darren.

[DaveH]

(04-28-2015, 04:15 PM)EdK Wrote: I guess I misspoke. My lead screw is pinned but not with a shear pin. It's pinned with a 3/16" spring pin with a breaking strength of about 4100lbs.  

Ed

This will get me into a lot of trouble.
Your lathe was designed by engineers made by machinists.

DaveH

[Pete O]

Is crashing as much an issue with the crossfeed as with the longitudinal feed? The drive gear on the leadscrew of my lathe is a slip fit with a tapered pin, so the drive is only transmitted by the pin. However if I introduce a clearance fit into the middle of the crossfeed screw, as it is only supported at either end, I think it would cause problems with sagging in the middle (like me).
I'm not sure I have the confidence to produce a tapered fit, I'm only going to get one chance at this (unlike the threading of the new nut, thankfully) and don't want to risk destroying the driven section of the shaft.

[Vinny]

Yes. I make plastic gears for the Logan gearbox. When I was first testing them I engaged the power crossfeed. It was up against the stop and I heard a snap. I don't wanna think about what it woulda sounded like if they were all steel gears! I also have an older Logan so it doesn't have the slip fit clutch and don't know what would have happened if I did. In the end I had one gear crack in half and the next day when I had more time I replaced it (without removing the gearbox) and was back in business. Unfortunately the next test didn't break the same gear, it broke a different plastic gear that's a pain the butt to replace. Morrow of the story, don't crash the lathe. Mine were intentional tho to test the strength of the gears. No more intentional stuff here now!

[Dr Stan]

(04-28-2015, 04:15 PM)EdK Wrote: I guess I misspoke. My lead screw is pinned but not with a shear pin. It's pinned with a 3/16" spring pin with a breaking strength of about 4100lbs.  

Ed

sounds like someone replaced the shear pin with a spring pin.  Not too difficult to correct.