G9729 Half Nuts

[tomh]

Can you post a pic of the back side of the half nut?
Is it held in place with a cross pin?
Looking at the manual, that lathe only uses one piece of what most is commonly known as a set. If so then its going to wear out rather fast because it is pushing /ridding and not clamping the leadscrew as half nuts are designed to do.
Folks have been making half nut from derlin/actel. The projects in metal group seem to be having success from what I have read,
so that might be a possible solution for you to look into.

Your leadscrew is 6 tpi

 

[LX Kid]

The feed lever, lower hand wheel, is engaged all the time! No way to disengage it. The half nut is engaged when cutting threads and the feed wheel turns as it moved along. With half nut "not" engaged I can not "easily" move my carriage by hand. I could try loosening the gib screws under the table, just above the gear box to see if they might be too tight. Being a "newbie" I could have tried to take too much play out of the carriage.

 

[LX Kid]

The carriage lock would not stay put, just flop around, unless held in place by hand so I made a mod to the shaft. This put friction on the gear box hole to hold it in place.

 

[tomh]

Without the half nut engaged the carriage should glide with out any effort when you move it with your hand, so I suggest loosen the carriage gib a little at a time till you can slide the carriage easily. The brass half nut has my curiosity up, can you post a pic of the back of the brass half nut.

 

[tmarks11]

Yet another reason to hate 3IN1 designs. Using the lead-screw and (half of a) half nuts for power feed is a trick found on cheap 7x14 mini lathes. turning.

What is even crazier is that the G9729 has the slot in the lead screw, so it shouldn't have to use the half nuts. But Grizzly put the "feed lever" (really the leadscrew engagement lever) on the headstock instead of the carriage. Only the cross-slide power feed uses the slot on the leadscrew; longitudinal feed relies on the half-nuts.

Even the 9x19 lathes have a separate feed lever (nothing to do with the half-nuts) on the carriage to engage/disengage the slot in the lead screw so you don't have to use the half-nuts for turning.

Since you obviously use your lathe a lot, you might start looking for a 12x36 to upgrade to. You will be very happy with the additional features.

The feed lever, lower hand wheel, is engaged all the time! No way to disengage it.

That is true on every lathe. The carriage hand wheel is engaged to the rack on the bottom of the bed all the time, moving the carriage moves the carriage hand wheel (whether while threading or by hand or by power-feed).

The "feed lever" on most lathes (as I said above) is mounted on the apron and is used to engage/disengage power feed (both longitudinal and cross).

 

[Bob Korves]

http://cdn1.grizzly.com/manuals/g9729_m.pdf
This is a link to the operation manual. Read pages 35-44. Page 35 shows the feed lever and what it does. I just noticed that the feed lever is part of the headstock, not part of the apron. You do not have a separate feed lever on the apron, like most lathes do. So the half nut needs to be engaged for any power movement of the carriage on your machine. The combination of a single half nut and the half nut being used for all power traversing is the root of your problem with half nut wear. It is a far from ideal design, apparently not designed for much usage. I would go back to your earlier idea of selling the machine if I intended to use it more than occasionally and even then only for light work.

Edit: Looks like tmarks11 beat me to it...

 

[LX Kid]

Ok, here is what I've discovered. I tried pushing my carriage by hand and I could not budge it! I "evidently" had the gib adjustments too tight. I adjusted the gib screws just to where I could move the carriage by hand. That said it's not as smooth as silk. When making cuts I will adjust the carriage lock for best final cut using power feed. Accuracy will suffer. Here is a pic of the back of the half nut and my pinion gear. I replaced the pinion gear early on cause it was really rusty and badly pitted. The new one wasn't much better!

 

[tmarks11]

Looks like tmarks11 beat me to it...

great minds think alike... just some people type faster than others...

 

[mmcmdl]

great minds think alike... just some people type faster than others...

Every time a see this thread title pop up I'm reminded of my current situation ! Rummaging thru drawers , containers , boxes , buckets and coolers looking for stuff I know I have has driven me past half nuts . Waaayyy past !

 

[tomh]

Lets try a couple ideas.
I hope this helps in some insane way

On the carriage are you getting plenty of oil on the bed ways between the carriage and the bed? think of the oil as millions of tiny ball bearings, it will help the carriage slide without causing friction/drag that can effect carriage movement and the cut finish.

Now for the half nut.
That is what I needed to see. looking at the manual and the half nut and wear on it, it appears that the halfnut rest in a cradle and held in place with a pin and that assembly possibly threads on to the half nut lever shaft? if so you should be able to adjust the halfnut assembly closer to or away from the lead screw, does that make sense or am I out in left field? the halfnut thread wear appears to be primarily on the outside of the thread if so I am thing that the halfnut needs to be closer to the lead screw.