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Machine PDM30 table nut stripped

Machine
Brian H

Brian H

Super User
It appears I have stripped the table nut on my X-axis. I noticed the table feed was a bit stiff about a week ago. I "inspected" the lead screw as best I could and nothing appeared out of order so I assumed it just needed a gib adjustment (this mill was brand new in May). I added some oil to the lead screw, adjusted the gib and it seemed a bit better. Then on Sunday it got really hard to turn the handle and all of a sudden the lead screw turned but the table didn't.
I have disassembled everything and removed the lead screw/table nut and all is piss wobbly slack (the nut will almost slide over the lead screw).
The table nut has a slit with a screw through it for some type of adjustment. I tried fiddling with this but it doesn't seem to make any difference. I have ordered a new nut. I would like some advice on how to prevent this occurring again in the future. What did I miss? I wasn't forcing a heavy cut, just moving the table.
I am definitely a newbie, and have only used a small bench mill till now, so I have been very cautious learning the capabilities of this new larger machine.
 
phaxtris

phaxtris

(Ryan)
Premium Member
Premium Member
More than a few of us have/had one of those, it's possible you just had a bad nut, or it was mis-adjusted from the factory (you said it has a slit/screw to adjust)
 
Brian H

Brian H

Super User
phaxtris said:
More than a few of us have/had one of those, it's possible you just had a bad nut, or it was mis-adjusted from the factory (you said it has a slit/screw to adjust)
Click to expand...
yes. I am attempting to add a picture (not successfully I might add)
 
Brian H

Brian H

Super User
YYCHM said:
That lead screw doesn't appear to have Acme threads? Was the nut firmly bolted/screwed down when you removed it?
Click to expand...
I tried a few different thread pitch guages and can't determine what it is.
Yes, everything was tight. One thing I did notice was the large amount of fine swarf in the threads, almost like steel wool. I don't see any damage on the lead screw threads but the threads in the nut are very shallow and almost flat.
 
DavidR8

DavidR8

Scrap maker
Administrator
Moderator
Premium Member
That looks to be a very fine thread for an Acme threaded lead screw. Are you able to measure the pitch?
 
Susquatch

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
The screw pitch looks about right to me.

The nut is called a split nut cuz it is split! As the screw in the split is tightened, it forces the two halves apart on one side which reduces the end play in the nut so its a tighter fit with less backlash.

If it's too tight, the nut will wear out too fast. It is supposed to be tightened every so often as the backlash gets bigger.

But you say it's a new mill. That makes it unlikely it was ever adjusted before and unlikely that is problem.

I'd suggest that you clean that big leade screw and then tell us (show us) how rough the threads are. That would be my first guess as to what happened. Basically, a rough surface on the screw ate the nut in short order. If so, a new screw and a new nut are required.
 
Last edited:
Xyphota

Xyphota

Ultra Member
Is it possible something fell/crashed into the table, or if it got bumped while you were moving something else heavy around?
 
Susquatch

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
Xyphota said:
Is it possible something fell/crashed into the table, or if it got bumped while you were moving something else heavy around?
Click to expand...

+1 on that idea. The nut could easily get stripped that way. And if so, it was a darn good thing it did. A new table is a bad outcome.
 
Proxule

Proxule

Ultra Member
The fine swarf is good, It took out the brass / bronze nut vs. the lead screw.
You could always count the threads in 1 inch of screw to get an idea of TPI.

You could buy a tap and make your own nut - Depends on how interested you are vs. how fast king sends one out.

I bet your nut was bad from the factory. That or some steel swarf got in there perhaps and mangled the threads.
Since its a split nut, you remove lash but pushing the 2 sets of threads apart. Could of gotten lodged in here, If that makes sense?

Gluck
 
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