G0752 Lathe Stuck Half Nut

RVJimD

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Dec 30, 2014
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While turning some mild steel the half nut/feed lever would not disengage. I managed to stop it before it killed me or itself.

I was turning some 3/4" steel to a shoulder and just as it came to the shoulder I went to pull up on the lever to stop and it was seized in the engaged position. I released the QC tool post and tool holder, still seized. Turned the Lathe back on and reversed direction and the saddle moves away from the headstock okay, but still can't release the half nut. Don't have time to mess with it today.

Has anyone had this trouble with this or any other Lathe?

Glad I was only turning to a shoulder and not working close to the three Jaw.

Jim
 

RJSakowski

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The 752 is basically the same machine as my 602 and no, I have never had this problem. It is possible that some debris has gotten into the mechanism and preventing disengagement. Is the lever jammed or does disengaging the lever not disengage the half nut(s)? If the former, I would look for debris., If the latter, perhaps a sheared pin on the half nut.
 

RVJimD

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RJ,

The lever is stuck in position (engaged).

Thanks for the response. I got around to looking at it this afternoon and it and apparently the detent ball was stuck somehow, probably partly out of the hole in the round part of the handle? Couldn't tell exactly since it all fell apart when I dropped the wedge and bottome portion of the saddle off.

I don't think it was out of adjustment but not sure, I would guess the handle was not tight and started sliding off, out toward the front of the machine, allowing enough of a gap between the handle and detent location that the ball was able to get lodged between the two, seizing the function? It never felt like it was loose and I never had trouble with it until this event.

I also found a small spot on the TOP of the wedge (shoot, what is that called, wedge isn't the proper term is it?) that might indicate a chip jammed in place freezing the half nuts in place? I couldn't move the handle at all.

I'm only a hobby machinist and I DIDNT stay at a Holiday Day Inn last night so there you go....

Be careful out there! Makes me think I should PRACTICE an emergency stop function from a hands normal position to hitting the stop! I know I didn't do that as an automatic response like I would have liked! Anyone hear of that sort of lesson in shops class or machine training?

Jim
 
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chillywilly

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No, haven't heard of that, but I like the idea of training or at least mentally preparing for that bad moment. Like looking down the road instead of at the car in front of you. Thanks for sharing
 

Bi11Hudson

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Early on in my learning to thread, I ran into a similar problem on a G-1550. That is the predecessor to a G-4000, a relatively small machine, from Grizzly, from Taiwan. The slowest speed for that machine was 140 RPM. As I threaded, the half nuts would "lock" up as the leadscrew was turning. I disassembled the apron several times looking for something off kilter. Eventually, I built a reduction gear assembly (40 RPM) and the problem went away. I can only assume that I was threading too fast.

The final assumption was that the "acme" threads on the lead screw were sharp, as were the threads of the half nut. This was a new machine. There is "tension" on such a new part and slowing it down created less tension. I don't know that was the problem, just an assumption. But slowing it down took care of the problem. The gear reduction I built isn't very pretty, but it works well. http://www.hudsontelcom.com/9X20Gear.html if you want to look at it. The assumption was based on many years experience working on machinery. Not something that can be expressed, just a feeling.

Bill Hudson​
 
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