Half Nut Adjustments?

[Wongster]

Hello folks,

I spent the morning before heading to church stripping the lead screw, carriage, and the apron apart. Beside wanting to make some adjustments to the gibs and slides to make the axes turn smoother, I also wanted to take a look at how the half nut works.

You see, I've been seeing the lead screw being lifted up everytime the half nut is engaged and wonder if this is the cause of the lead screw handwheel not being able to turn smoothly. So the plan was to adjust the gib plate underneath the carriage so that it glide smoothly on the ways and put the apron back on to isolate the problem.

After spending quite a long time, I managed to get the carriage gliding smoothly with no lifting and side movement. When the apron was put back and half nut engaged, turning the handwheel is still a pain.

I'm unable to strip the half nut as it seems that the 4 pins on it are holding it down very tightly on the apron. When I look at the exploded diagram in the manual, I don't see anything that can be adjusted. The idea I had was to "move" the half nut up a little so that it is in line with the lead screw and so ease off the friction. I may have think wrong though...

Here is the exploded diagram from the lathe's manual:



Using Babel Fish, I've listed out the terms used:
P/N
36 - Klemmmutter: Clamping Nut
37 - Blech: Sheet Metal
38 - Nocke: Cam
56 - Stift: Pin
57 - Madenschraube: Set-Screw

The pics from this morning session can be found on my blog here

Before going on to making the ER32 collet chuck, I wish to get this arm-cramping-hard-turning of the handwheel out of my life.

Any help would be very much appreciated.

Regards,
Wong

[Highpower]

Wong,

With the apron removed, did the saddle move smoothly from end to end - or was it looser towards the center of the bed?

Did you check to see if the lead screw is straight and not bowed in the center?

I had a similar problem with my mini lathe lifting the lead screw when engaged. I just added some shim stock between the saddle and the apron in order to "center" the half-nuts over the lead screw. FWIW.

Willie

[Wongster]

Willie,

Thanks for the shim stock idea. It may just work. I'll test it in my next session.

The saddle did move smoothly with little effort pushing and pulling it from between the ways. It is harder if I push or pull from the side where you have the lead screw underneath. It gets a little tighter very near to the spindle but I don't usually cut that close. No apparent bow in the lead screw. Pretty straight at the moment.

One thing I noted when the apron and lead screw was re-installed; turning the handwheel to move the carriage from left to right is always easier than from right to left. Don't know if this is of any significant.

Regards,
Wong

[Highpower]

(04-22-2012, 10:14 AM)Wongster Wrote: One thing I noted when the apron and lead screw was re-installed; turning the handwheel to move the carriage from left to right is always easier than from right to left. Don't know if this is of any significant.

Regards,
Wong

Hmmm.... probably unlikely but the rack teeth (attached to the bed) may be sitting lower on the left end of the bed, causing it to bind on the pinion gear in the apron? Try the shim stock and see if that improves the right to left movement any. (Wild guess...)

[DaveH]

Wong,
Here's my best guess the half nuts may just slide out.
The 4 pins are for location, Proxxon went to a lot of trouble to locate it correctly. So caution is a wise option at the moment.

Test for the half nut engagement at the headstock, the middle (1/2 way between headstock and tailstock) and at the tailstock. See if you get the same amount of movement of the lead screw at each position.


DaveH

[DaveH]

(04-22-2012, 09:31 AM)Wongster Wrote: When the apron was put back and half nut engaged, turning the handwheel is still a pain.
Regards,
Wong

Wong, I think you're right it is a pain, once the half nuts are engaged you should not turn the hand wheel, you will break some thing

Dave

[Wongster]

(04-22-2012, 10:26 AM)DaveH Wrote: Wong,
Here's my best guess the half nuts may just slide out.
The 4 pins are for location, Proxxon went to a lot of trouble to locate it correctly. So caution is a wise option at the moment.

I should leave the 1/2 nut alone then. Not worth the risk.

(04-22-2012, 10:26 AM)DaveH Wrote: Test for the half nut engagement at the headstock, the middle (1/2 way between headstock and tailstock) and at the tailstock. See if you get the same amount of movement of the lead screw at each position.

The feel when engaging the half nut at the tailstock is like I'm locking up the lead screw. At the middle, the lead screw shifted up. I'll take a look at it at the headstock.

(04-22-2012, 10:50 AM)DaveH Wrote: Wong, I think you're right it is a pain, once the half nuts are engaged you should not turn the hand wheel, you will break some thing

Dave

Dave, I need to engage the half nut to turn the lead screw handwheel and not the handwheel at the apron.

[DaveH]

(04-22-2012, 05:18 PM)Wongster Wrote: Dave, I need to engage the half nut to turn the lead screw handwheel and not the handwheel at the apron.

Wong,
I knew that really, I was just testing

That's fine Wong, my mistake

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

[Wongster]

Dave,

Did I pass the test? No mistake there, Dave. Good reminder. I was wondering why didn't the handwheel on the apron turn with the half nut engaged when I first got the lathe. I don't have such on my Sherline...

I couldn't figure out that part on not being able to remove the half nut altogether. From the diagram, it should. Maybe it is just too tightly fit. A good buddy of my blog pointed out that I may need to use 2 one-sided razor blades to carefully knock it out of the 4 pins used for alignment. From the diagram, it seems that there is no adjustment available even with it apart. So unlikely I want to risk not being able to put it back properly.

Over at the other forum, I posted the exploded diagram of the lead screw assembly when Andyf suggested lifting the leadscrew. I've it here to see if I can gather more suggestions before my next session to hopefully correct things.



Regards,
Wong

[DaveH]

Wong,
Yep, lifting the lead screw at the tailstock end is a far better idea than trying to adjust the half nuts.

You still need to check if lifting the leadscrew at the tailstock end is the right way to go.
Slow and carefull is the way to go

DaveH