Half Nut Adjustments?

[Wongster]

Dave,
What about shimming the apron to move the whole assembly down to the lead screw's level?

Regards,
Wong

[stevec]

(04-22-2012, 05:27 PM)DaveH Wrote: Just to labour the point and clear it up for me, those half nuts slide open and close, what stops them from sliding out altogether?


DaveH

Dave, my take is, if Wong can't remove the slides/plates for the half nuts because of the tight dowel pins then the half nut pins remain in the spiral slots of the half nut actuator (part# 38) and nothing slides out.

[stevec]

The only problem I can see with shimming down the apron front plate is it will result in less engagement with the rack.
The answer there might be to shim the rack down equally but I guess that would require slotting the screw holes (if they aren't already).

[Wongster]

Steve, the rack has some room in those holes. I'll take a closer look.

When turning without the auto feed, do you folks use the lead screw handwheel or the one at the apron?

Regards,
Wong

[DaveH]

(04-23-2012, 07:52 AM)Wongster Wrote: When turning without the auto feed, do you folks use the lead screw handwheel or the one at the apron?
Regards,
Wong

On my lathe and many others I can only use the hand wheel on the apron, I don't have a hand wheel to turn the lead screw.

Your lathe is considered a high end precision lathe, so we need to be sure we are correctly addressing the problem and not just the symptoms. We know the half nuts lift the lead screw, we just have to find out why. Whether it is the apron, or the lead screw or something else we really should be sure before changing any thing

DaveH

[Wongster]

I took a closer video showing the movements.





There is no available adjustment on the tailstock end of the bearing holding the lead screw. On the rack, there may be some small amount allow to adjust it.

On Jan 2, this year, Proxxon replied to my mail on the proxxon:

Thank you very much for your message. As you describe the problem, we can only think of one possible reason: The toothed rack below the leadscrew is most likely not aligned correctly. This problem can be fixed quite easily:

1. Please open the 4 screws as shown in attached picture
2. Then retighten these screws again step by step from left to right, while pressing the rack to the top. For this, you should press a slotted screwdriver from below in the teeth of the rack und push it upwards.

When the rack is aligned perfectly again (i.e. pressed tight to the top on all 4 screws), the carriage should work smoothly again. You can support this with a drop of light machine oil on the leadscrew and the handwheels.

When I asked about the movement of the lead screw when engaging the half nut, he replied saying that "This is quite normal, a bit of movement of the leadscrews does not affect the turning of the handwheels."

Regards,
Wong

[stevec]

I'm appalled that they would reply "The toothed rack below the leadscrew is most likely not aligned correctly. "
Hard to have faith in a person who doesn't know the orientation of the parts of the machine.
Wait... are you below the equator?

Excellent video documentation of the leadscrew movement!

Can you get an idea of the amount of shimming that would be required by using a dial indicator on the leadscrew "lift"?
I'd try that and see if you binding is eliminated. If it is, then check the engagement with the rack and, using the mounting slots, align it?

[EdK]

(04-23-2012, 11:28 AM)stevec Wrote: I'm appalled that they would reply "The toothed rack below the leadscrew is most likely not aligned correctly. "
Hard to have faith in a person who doesn't know the orientation of the parts of the machine.

Isn't that a rack below the leadscrew in the video? I can't imagine why there would be a rack there but it sure looks like one.

Ed

[Wongster]

Steve, Ed, the rack is indeed below the lead screw. I don't know about the "usual", this is my first lathe with handwheel at the apron (do you call this an apron handwheel or carriage handwheel?).

Regards,
Wong

[EdK]

(04-23-2012, 12:03 PM)Wongster Wrote: Steve, Ed, the rack is indeed below the lead screw. I don't know about the "usual", this is my first lathe with handwheel at the apron (do you call this an apron handwheel or carriage handwheel?).

Regards,
Wong

Wong,

That's usually called the carriage hand-wheel. The apron contains the hand-wheel assembly. The carriage assembly is made up of the apron and saddle assemblies.

Ed