G4000 Leadscrew Binding

M

mtrhead

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Hi, I bought a used G4000 Grizzly. When started to get the feeds and threading working I ran into an issue with the leadscrew where it binds particularly when the carriage is run over to the left near the headstock. I took off the leadscrew and apron. Cleaned the chips out of both, partially straightened the leadscrew and reassembled, by eye it still has a .030" whip in it. When I tighten the apron to the carriage things bind up, to where you can't turn the leadscrew by hand. With the carriage in the middle it loosens up and it is real nice towards the right end of the travel. I'm planning to make some shims, from .012" brass to put between the apron and carriage. Has anyone else run into issues like this, anything to check that i may be missing? I'd really like to avoid messing with the mounting of the ways and headstock, it faces good and the cuts across the work are straight enough for the projects I'm planning. I haven't unbolted the gearbox yet to see if i can raise the left end of the leadscrew a bit by messing with it's mounting position.
 
I have not used that lathe. But .030 is a lot if the bend is close to the head stock. I would try to get it within .005. Does the carriage move freely with the half nuts disengaged ?
 
kd4gij said:
I have not used that lathe. But .030 is a lot if the bend is close to the head stock. I would try to get it within .005. Does the carriage move freely with the half nuts disengaged ?
Click to expand...
The bend is towards the middle and not a major contributor to this issue. The leadscrew binds with the half nuts and the feed both disengaged. The bind is worst with the carriage to the left. If i crack loose the two mounting screws between the apron and carriage the bind goes away.
 
Ok loosen the 2 screws on the bracket, run the carriage all the way back to the tail stock end. Close the half nuts and then tighten the bracket. That should line it up.
 
What ever you do, don't place shims between the apron and saddle. Doing so messes with the mesh of the gearing in the apron. Will cause premature failure of a gear or two over a short period of time.
You're probably going to have to drop the QCGB down by the amount needed to get things lined up.
 
4gsr said:
What ever you do, don't place shims between the apron and saddle. Doing so messes with the mesh of the gearing in the apron. Will cause premature failure of a gear or two over a short period of time.
You're probably going to have to drop the QCGB down by the amount needed to get things lined up.
Click to expand...
Oh hey, thanks. I'll take a look inside the QCGB the next time I tackle this.
 
If you you have a bent screw take it out and make it straight. It most likely got bent moveing it.
 
You could also just call Grizzly parts and buy a new leadscrew don't know what the cost would be but would save a lot of messing around in the long run.
 
When I got my Clausing/Atlas Mk2, it had a bind, as you suggested, moving toward the head. I wound up shimming the left end bushing on the lead screw, about .025 away from the head. Since the change gears are adjusted individually, the location didn't matter to them, but the saddle distance is fixed and that bound.
 
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