Half nuts disengage by themselves

Wear and/or maladjustment. How much backlash does the closed half-nut have? (This ordinarily does not matter unless one is making very accurate and long screw threads, but is used to gauge wear.)

Joe Gwinn

Joseph Gwinn fired this volley in news:joegwinn- snipped-for-privacy@news.giganews.com:

Iggy, odds are you'll find almost no thread at all in the half-nuts. As they become severely worn, the will tend to "hop" out of engagement. There's only one solution -- replace them; if you're really in a pinch, you can re-make the parts, but I'd look for replacements first.

LLoyd

And one additional point: If it does come down to making the replacements, and you have to make them on the same lathe, MAKE THEM NOW! Once the half-nuts won't hold engagement at all, you're screwed.

First things first. Have you ever cleaned them? I've seen half nuts pack up with swarf and gummy oil so much that they would not engage fully. A good cleaning may make them almost as good as new. Or not.

John Martin

Joe... Thanks... I called Clausing and talked to Tito. He told me to first clean the leadscrew very well and check the wear on slots of the round slotted circle that closes half nuts.

This leadscrew proved exceptionally difficult to clean, in fact, I may just take it off and use a powerwasher or take it to a hot shower. I spent a lot of time cleaning it and it is still not as clean as it should be.

The half nuts are $100 from Clausing, so even if they are bad, it is not the end of the world.

i

A few points of note.

1) New half nuts are $100 from Clausing (and I think they include a new slotted circle for engaging them) 2) I have an extra pair of worn half nuts that came with the lathe 3) I think that you guys are right, I will try to take off the carriage and apron and look at half nuts. Taking that stuff off will be beneficial in other ways, such as cleaning the sliding surface, etc.

If you have the lathe running, set it to a slow speed/feedrate and wrap a piece of heavy cotton cord ONCE ONLY around a groove in the leadscrew at one end; pull hard on the cord; traverse the cord to the other end.

Soaking it in paint thinner, or, in a pinch, WD-40, will help clean out a lot of gunk.

And look for settled gunk in the apron.

Regarding taking off apron: I did try this once.

It did not work: the "carriage locking screw" would not unscrew all the way.

I did not want to force it and I had other issues, so I gave up and moved on to other things, but now is the time to look at it.

The carriage locking screw connects to a plate under the carriage, so that when you tighten it it grabs the bed.

The screw unscrews, but stops midway and I wanted to know if I am doing something wrong or should just use a bit more force.

i

AND DON"T WRAP THE CORD AROUND EITHER HAND!!

Attaching the cord ends to the end of a board and holding the board would add a safety factor, and let you pull harder.

Dave

The half nuts on my Wards/Logan were gunked like that . Crud between the halves blocked them closing all the way . Makes 'em wear faster too .

If your half nuts are in good shape, crap/chips embedded in the half nuts.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

That is an excellent suggestion! Btw, if you haven't seen his model of lathe, it has a rather fine pitched lead screw so a bit of dirt is a lot of dirt.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

An old, old trick.

I don't remember it, but that would make it even more suitable. That's how I clean the screw on my SB.

I know, and I've heard it before but the other day when I looked at my screw that is the same only other then shorter, I couldn't remember that trick for cleaning.

I guess you win the been around long enough to know that one award. No monetary value. ;)

That is going to be my way on my lathe also.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Classic case of worn half-nuts. But, take the whole mechanism apart, there may have been a detent mechanism that has gotten gummed up or worn. If not that, then it is likely due to wear of the half-nut threads that are now pushing the nuts apart. It could also be a misalignment of the nuts to the leadscrew, swarf packed into the half nuts preventing them from fully closing or something like that.

Jon

Geez, I'm not sure. Is this a classic Atlas, or a Clausing industrial lathe? I know the Atlas pretty well, I'm the moderator of the Atlas-Craftsman group on Yahoo. I wouldn't be too surprised if there is something to prevent the clamp plate from completely unscrewing and falling into the half-nut mechanism. I don't think the Atlas had such a protection. Anyway, you should be able to run the carriage at least partly off the right end of the bed to examine the parts. Take the tailstock off and then remove the right-end leadscrew bracket.

Jon

One trick is to grind a small screwdriver or similar piece to match the thread, and then run the lathe at low speed and hold the tool in the groove. A keyed Acme screw is a little harder to clean this way, but it definitely works. If swarf is packed totally hard in the screw, water won't get it out, anyway, and that is likely part of the threading trouble. If the screw is packed with rammed-in chips, the nuts will be worse!

Jon

Hmm? It would almost have to be either 8 or 16 TPI for Imperial thread pitches.

Jon