Horror Stories About The Chuck Coming Off While Running Backwards

[janvanruth]

Every now and than in a thread it shows up: warnings that you cannot run a screwed on chuck backwards while threading, because it will unscrew and reek havoc.

Now, who has actually SEEN this happen.
I mean SEEN, not heard about it.
And SEEN not on a monster lathe taking .050 passes on a giant thread, but on a normal lathe taking 0.005 passes on a normal thread.

I will tell you that, other than the fool who put the chuck on just before threading and did not tighten it,
NOBODY will have seen it happen.

Next time you are threading switch off the engine and turn the chuck by hand using a spanner on a jaw.
Now after the threading is done ,block the backgear and try to unscrew the chuck using the same force on the same spanner......

 

[stupoty]

I had a chuck stuck on my new (to me lathe) after freeing it by cutting it off and repairing the back plate I was ready to set up my vfd.

I can program the ramp up and down time on my vfd.

I set it to stop in about 1.5 seconds.

I ran the lath up to speed.

I stoped it.

I began too poop myself. (The 8 inch chuck didnt stop when the spindle did and was now unscrewing)

I crashed the lath tool into A piece f stock held in the chuck to stop any damage, that worked ok

I now have my de acell set to about 5 seconds, it hasn't happnd again.

Running in reverse, hummmm I think I will give that a miss for now.

I'm reckoning if their was any cutting force on a work piece running backwards it would unscrew very quickly.

Stuart

 

[janvanruth]

I had a chuck stuck on my new (to me lathe) after freeing it by cutting it off and repairing the back plate I was ready to set up my vfd.

I can program the ramp up and down time on my vfd.

I set it to stop in about 1.5 seconds.

I ran the lath up to speed.

I stoped it.

I began too poop myself. (The 8 inch chuck didnt stop when the spindle did and was now unscrewing)

I crashed the lath tool into A piece f stock held in the chuck to stop any damage, that worked ok

I now have my de acell set to about 5 seconds, it hasn't happnd again.

Running in reverse, hummmm I think I will give that a miss for now.

I'm reckoning if their was any cutting force on a work piece running backwards it would unscrew very quickly.

Stuart

while threading?

 

[Jeff M]

I didn't see it happen but I saw the splinted thumb and finger of a coworker who worked nights in the shop I worked in around 1980 that had the thread mounted chuck on a 10" south bend lathe that unscrewed and broke his thumb and finger. I don't remember what he was doing but it happened. I don't do it.
I have seen a bridgeport boring head unscrew from the R8 holder because he was running it backwards. He was lucky that he was not hurt.

 

[stupoty]

while threading?

No not whilst threading. I wasnt taking a cut at all.

So if it can unscrew from stopping to fast i would definetly not try cutting with the drive in reverse.

I've had the tool post slip during threading cuts at low tpi so theirs a lot of force involved in it.

You could do it between centres if u want to run reverse or maybe put a draw bar clamp arangement on the chuck so it cant unscreww.

I belive some threaded spindle lathes have a locking pin mine dosnt though.

I've only dropEd my 8 inch chuck once. It destroyed everything in its path untill it stopped

Play it safe sometimes . It good for you

Stuart

 

[Mark in Indiana]

I've had a pressed in chuck fall out of the drill press because the drill bit was slightly bent and caused a vibration to loosen it.

 

[george wilson]

Of course,the chuck unscrewing,like everything else,depends upon variables. How tight was the chuck screwed on,etc. I have run a screw nose lathe backwards to do threading and turning,but I know how to get away with it.

 

[gr8legs]

I had the chuck on my 12" Atlas unscrew while running in reverse. Of course it can happen, it's a screw thread - that's how they work!
For me this was one of the prime reasons to upgrade lathes when I could to one with a cam-lock spindle.

Stu

 

[Bill Gruby]

The screw on chucks CAN and Will unscrew running in reverse at any given moment if you are not careful, even when threading. All that has to happen is for the tool to grab. I have SEEN it happen a few times during my career. The age old adage comes into play here, just because you haven't seen it, does not mean it didn't or can't happen.

"Billy G"

 

[chips&more]

I’m in 100% agreement that a screw on chuck will un-screw. And will un-screw even when you do not want it to. And in addition to threaded stuff. Please be aware that there is other tooling that also uses threads for attachment in the shop. Like boring heads. Many boring heads have screw on arbors. Just the other day I put Locktite on a Bridgeport #1 boring head arbor so it would not un-screw on me when I needed to run the head in a CCW direction…Dave.