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How safe is holding stock with jaws reversed on lathe

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Chris TickTock16/07/2020 12:03:36
480 forum posts
31 photos

Hi Guys,

I am still investigating various means of holding stock on my little Sherline lathe. On the 3 jaw chuck the jaws can be reversed to byte into (clamp) on an internal recess or tube.

This is not as safe to my mind as safe as putting the stock beteen the jaws in their normal position.

Anyone care to convey their experiences?

Chris

Brian H16/07/2020 12:10:26
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1676 forum posts
109 photos

Hello Chris, you're safe enough with thinnish items but will get problems with longer pieces unless they are supported by a tailstock centre or a steady. Anything that is no thicker than the length of the jaw should be fine.

Brian

colin hawes16/07/2020 12:26:53
509 forum posts
18 photos

Depends how thick the tube wall is, thin walls can easily be distorted under cutter force causing the chuck to lose it's grip .Colin

not done it yet16/07/2020 12:38:20
4747 forum posts
16 photos

Of course they are safe - as long as used within safe limits, or they would not be supplied. Even the usual jaws can be unsafe, if the machine is used improperly.

It surely must be clear (to most) that the further the work-piece is held within the jaws, the safer it 'should' be. There will be exceptions, of course.

JasonB16/07/2020 13:02:09
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18323 forum posts
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Actually Chris the main reason your jaws can be reversed is so you can grip the OUTSIDE of larger items not so that the full depth jaws are holding the inside of tube.

Chris TickTock16/07/2020 13:31:50
480 forum posts
31 photos
Posted by JasonB on 16/07/2020 13:02:09:

Actually Chris the main reason your jaws can be reversed is so you can grip the OUTSIDE of larger items not so that the full depth jaws are holding the inside of tube.

Very helpful posts thanks . The reason why I ask is looking at this flat disk of aluminium photographed here I have it is 25mm thick with a recess on one side  I presume that was used to cut it?? To me it looks a dangerous practice, albeit you could use the tail stock against it.

Chrisaluminpic.jpg

Edited By Chris TickTock on 16/07/2020 13:33:22

Andrew Johnston16/07/2020 13:56:49
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5558 forum posts
650 photos

Only the man who tightens the chuck knows how big a cut can be taken.

This casting is being held on a 1/16" wide internal step with the jaws reversed (8" 4-jaw chuck); I can't remember what the DOC was, but looking at the cut in progress probably 30 to 40 thou:

face_profiling_me.jpg

Andrew

Chris TickTock16/07/2020 15:15:42
480 forum posts
31 photos
Posted by Andrew Johnston on 16/07/2020 13:56:49:

Only the man who tightens the chuck knows how big a cut can be taken.

This casting is being held on a 1/16" wide internal step with the jaws reversed (8" 4-jaw chuck); I can't remember what the DOC was, but looking at the cut in progress probably 30 to 40 thou:

face_profiling_me.jpg

Andrew

Thanks Andrew and your right with your use of the word 'Know' which having looked it up means being familiar with.

Bodes not so well for a novice....but I wonder how many more experienced guys have push their luck a tad too far before they adjusted their knowledge?

Chris

SillyOldDuffer16/07/2020 17:27:06
5939 forum posts
1282 photos
Posted by Chris TickTock on 16/07/2020 15:15:42:
Posted by Andrew Johnston on 16/07/2020 13:56:49:

Only the man who tightens the chuck knows how big a cut can be taken...

Andrew

...

Bodes not so well for a novice....but I wonder how many more experienced guys have push their luck a tad too far before they adjusted their knowledge?

Chris

All of us Chris! All of us. I've had two serious frights due to work coming out of the chuck, and many instances of work being spoilt due to it bending under cutting pressure. One fright I got away with, the other stripped the two speed gear set inside my mini-lathe's headstock.

Rules of thumb:

  • I don't like unsupported work protruding more than 5 times it's diameter from a chuck.
  • Chuck jaws need to have at least 3 teeth in contact with the scroll.

After that, think and test. It's the operators job to ensure work is held securely and judge the risk. Any sign of movement means a risk has to be managed. It's a big subject; faceplates, clamps, glue, steadies, the need to balance odd shaped jobs, gripping securely without crushing, the possibilities are almost endless. Particularly tricky deciding how to hold delicate, or heavy, or oversized, or awkward shapes securely. Well worth reading Sparey and Tubal Cain's Workholding in the Lathe, but in the end you have to develop a feel for what works. It's like the difference between Theory and Practical parts of the Driving Test: one of them is hard to pass without knowing the Highway Code AND learning to drive a car on real roads.

Dave

Chris TickTock16/07/2020 17:46:33
480 forum posts
31 photos
Posted by SillyOldDuffer on 16/07/2020 17:27:06:
Posted by Chris TickTock on 16/07/2020 15:15:42:
Posted by Andrew Johnston on 16/07/2020 13:56:49:

Only the man who tightens the chuck knows how big a cut can be taken...

Andrew

...

Bodes not so well for a novice....but I wonder how many more experienced guys have push their luck a tad too far before they adjusted their knowledge?

Chris

All of us Chris! All of us. I've had two serious frights due to work coming out of the chuck, and many instances of work being spoilt due to it bending under cutting pressure. One fright I got away with, the other stripped the two speed gear set inside my mini-lathe's headstock.

Rules of thumb:

  • I don't like unsupported work protruding more than 5 times it's diameter from a chuck.
  • Chuck jaws need to have at least 3 teeth in contact with the scroll.

After that, think and test. It's the operators job to ensure work is held securely and judge the risk. Any sign of movement means a risk has to be managed. It's a big subject; faceplates, clamps, glue, steadies, the need to balance odd shaped jobs, gripping securely without crushing, the possibilities are almost endless. Particularly tricky deciding how to hold delicate, or heavy, or oversized, or awkward shapes securely. Well worth reading Sparey and Tubal Cain's Workholding in the Lathe, but in the end you have to develop a feel for what works. It's like the difference between Theory and Practical parts of the Driving Test: one of them is hard to pass without knowing the Highway Code AND learning to drive a car on real roads.

Dave

Dave, appreciate the post and your honesty. In life I generally think when taking a risk what is the downside risk. With heavier stock on a lathe it it gets lose could be very serious as well as costly. Currently improving my knowledge of holding stock with faceplates, loctite, etc as I know all this knowledge is crucial if you employ it.

Chris

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