Chuck and the ACME Screw Split

[w1vlf]

Hello All,

Seems to me someone made the comment on my previous post about a 3 jaw chuck" Did someone tighten that chuck with a breaker bar?"
That seems more likely the as look at the problem with my 4 jaw chuck.

One of the ACME thread adjusters in my 4 jaw 8" Wescott chuck is split where the key inserts. It also affects the threads and causes that particular jaw to bind.

For a really quick fix I ground the offending threads and reassembled the chuck. I would like to fix this. Found a piece of 5/8" - 10 left hand ACME rod on Ebay.

When you look at the turned down section in the middle of the screw, there is a little shoulder where the threads start up.
The threads seem to fade in at that point and I am not sure I can do that.

I have attached photos so you can see what I am talking about.

Thank you
PauLC

[w1vlf]

Whoops one file was to big
Here it is

Also I am thinking that this screw is 5/8" 10 TPI LH

[SteveHGraham]

I was the one who made that guess. I wonder why someone would abuse a chuck like that. What kind of operation could make a workpiece spin so badly you would need to tighten the chuck with a breaker bar? Especially a 4-jaw, which is stronger than a 3-jaw to begin with.

Maybe the operator was just untrained and always overtightened.

[ctwo]

never know, maybe the key went half way around the block and met the ways.

[Harold_V]

Found a piece of 5/8" - 10 left hand ACME rod on Ebay.

Something you are overlooking is that the piece in question will require heat treating. If it is used in the soft condition, it will fail quickly.
Armed with that thought, it is most likely that the material you mentioned will not be capable of being heat treated, although it may be capable of being pack hardened. Not a great choice.

Note that I did not say it won't work---I just expect it will fail early on, with far less punishment than it may be called upon to receive.

Harold

[w1vlf]

hi Harold,
This the piece I was going to buy.

http://www.ebay.com/itm/5-8-10-LH-Acme- ... 46270cc19b

I don't know a lot about hardness but when I removed the original screw I hit it with the edge of a screw driver and it deformed rather badly.
A file grinds the screw metal rather easily.

Where would I find the correct material or the exact piece?

PauLC
W1VLF

[BadDog]

I don't know a lot about hardness but when I removed the original screw I hit it with the edge of a screw driver and it deformed rather badly.
A file grinds the screw metal rather easily.

Then I would say you've found your reason for the failure, and clear support for Harold's assertion regarding use of soft screws.

[Harold_V]

Yep! I agree with BadDog. The failure is most likely because the builder cut every possible corner. Such objects really should be hardened, to prevent deformation and premature failure, just as you've experienced. Can't be too hard, either, otherwise it would lack shock strength. If I was to guess, I'd say something around 50Rc would be good---with the component made from 4140. I expect you'd be hard put upon to find the threaded material made of that material, however.

With that in mind, buy the material you found and give it a go. It won't be any worse than what you have, and will most likely serve well enough. Just keep in mind that the material isn't heat treated, and will be easy to damage (which is quite obvious). Mean time, keep your eyes open for a better quality chuck.

Harold

[stevec]

I agree with Harold, at that price give it a go. The only problem might be how do you plan to make the square "socket" for the chuck key? Drill and then machine corners with a small end mill?

[wlw-19958]

Hi There,

If I was to guess, I'd say something around 50Rc would be good---with the component made from 4140. I expect you'd be hard put upon to find the threaded material made of that material, however.
Harold

Green Bay Mfg. Has Acme threaded rod in several different materials
(Including 4140). They offer .625 x 10 in both left and right hand thread.
You have to scan down the catalog page to the 4140 section.

Good Luck!
-Blue Chips-
Webb

[tornitore45]

When you look at the turned down section in the middle of the screw, there is a little shoulder where the threads start up.
The threads seem to fade in at that point and I am not sure I can do that.

A little file work can soften the thread start/end. I suppose the feature is to allow the tread to keep riding over the discontinuity in presence of slop between the jaw and the crew threads.

[ctwo]

I agree with Harold, at that price give it a go. The only problem might be how do you plan to make the square "socket" for the chuck key? Drill and then machine corners with a small end mill?

Maybe drill and then single point broach (is that a term)?