Thread: Lathe chuck swapping issues (face plate on threaded spindle)

So, I have a Hercus, whose spindle is an 8tpi thread, and 1.5" OD?
Tried to borrow and fit a 4jaw chuck, from a Boxford lathe.


1) Had a hell of a time getting my existing 4" chuck off. Tried gripping the drive belt, then hammering a wedge in the headstock under the pulley, then engaging the back-gears. This faceplate seems to lock on to the step in the spindle, so I will try oiling spindle before re-fitting (both threads are clean)

What do other people do to get threaded face plates off? How do you "lock" the spindle?



2) The borrowed chuck wound on about three quarters of a turn, and stopped. Its threads are clean.

On the bench:
IMG_0238.jpg
the Bernard 4 jaw (on the left) has a thread which is about 10 thou smaller in diameter than the Pratt (on the right).


Have any of you guys noticed such a variation between face plates or spindles?

I haven't measured the two spindles accurately yet (only have 1" micrometers),
but does it really mean the Boxford I borrowed this from has an undersized spindle AND faceplate?

Depending on age and origin, the threads could be Whitworth or UNC. If your lathe is UNC and the Boxford is WW, then the thread profile could cause a problem.

Bob L had a thread a while back where an old school fitter removed a stuck chuck that had resisted everyone else's efforts. From memory it was repetitive tapping that did the trick

Michael

Thanks Michael – good idea.

I checked my spindle with the thread gauge. It seemed to be 8tpi WW.


The internal threads (inside the face plate) are harder to see. Thread gauge seemed to clean a little rubbish out of the Bernard/Boxford thread, but picking 5° difference in there is a challenge with my eyesight

Has the face plate been left on the spindle for an extended period of time or are you trying to remove it after it's use?
The Boxford is Whitworth it will not fit on unless forced.

Originally Posted by pipeclay

Has the face plate been left on the spindle for an extended period of time or are you trying to remove it after it's use?
The Boxford is Whitworth it will NSY fit on if forced.

It was on my spindle for a few weeks, which included 6 or 8 hours turning. Not rusted on, spindle still shiny steel. (face plate threads still grey/black machined iron patina)


Maybe I should just fit a reversing switch, and let acceleration vs inertia do the trick?

Hi Guys,

I've pointed out many times in the past that screw on chucks have to be scrupulously clean and the register and threads kept well oiled. It takes very little to jam a chuck or a faceplate onto the spindle. Of course the other issue is that in use, particularly if you a doing an interrupted cut the hammering will cause the chuck to tighten up without your noticing it. I make a point of checking every now and then that the chuck can be loosened.

This is very important if you are using a water based coolant, because of the risk of rust on the inside of the threads. I tip I was given was to rub a film of grease around the threaded end of the spindle inside the chuck to prevent any coolant remaining on the end and migrating into the threads.

As far as removing a chuck or faceplate is concerned I generally just put the lathe into back gear and a quick tug on the chuck key is all it takes to unscrew it, the face plate I just grab the edges and twist. With the catch plate a short length of wood between the centre and catch pin is all it takes if its a bit tight.

I would suggest that you remove what ever you have on your spindle when finished machining, if the machining is going to take a period of time I would suggest removing work holding devices when you have finished for the day, I have never experienced any problem removing any of my work holding tooling from my Hercus spindle.

https://metalworkforums.com/f65/t199...19#post1909119

This was it

Michael

I have read that some people put a brown paper joint on the shoulder of the spindle. The chuck/faceplate then tightens onto the joint. This may be stops that tightening effect from interrupted cuts.

Phil

Sent from my Lenovo YT-X703F using Tapatalk

Originally Posted by Slatept

I have read that some people put a brown paper joint on the shoulder of the spindle. The chuck/faceplate then tightens onto the joint. This may be stops that tightening effect from interrupted cuts.

Phil

Sent from my Lenovo YT-X703F using Tapatalk

It can also provide a small gap of a few thou if burnt away to provide clearance for removing a stuck chuck or similar.

Hi Guys,

I would have thought that using a paper packing between the joint surface behind the register would have the opposite effect, since it would compress slightly under load.

A method for removing stuck chucks from threaded spindles is described here:

https://www.practicalmachinist.com/v...torial-165028/

See also Message #39 on that thread, featuring a 9 inch Hercus and a slightly modified method.

1) Thanks for that link Nadroj. An alloy clamp on the spindle (and rosin to help grip?) is probably safer than any tapping of the chuck end with a hammer. I might make one that fits on the teeth on the end.
Back where change gears do not engage:
IMG_0286.jpg



2) After removing it last time, I did oil the threads well. No easier to remove it, though.



3) I also had to disassemble the chuck to clean it after my last machining task (turning a washer into a saw blade adapting bush put a lot of small chips past the jaws and into the scroll). Will have to stuff the chuck with paper – to stop ingress of chips – next time.



4) Did finally roughly measure the spindle and my chuck;

Spindle 1.49" diameter.

Thread valleys 1.38" (diagonally across one turn).

Faceplate which doesn't fit: 1.33" between thread peaks.



5) After disassembling, cleaning, and refitting original chuck, it is now well and truly stuck again. Sigh.

Hi Nigel,

When you put the chuck back on, did you feel any resistance ? If so you need to stop and find out why. The tiniest bit of damage, swarf, dink in the threads on either chuck or spindle risks it jamming. Its so easy to burr something when removing or refitting a screwed on chuck.

As far as swarf in the scroll, that one is easy ! Just get a chopstick and sand one end down to fit into the scroll. Remove the jaws and run the end of the chopstick up or down the scroll. It will remove any debris and clean the bottom as well as the sides of the scroll.

No resistance - went on smoothly until it hit the shoulder past the thread (register).
Based on advice here, I didn't tighten - just turned on by finger.
But, after actually machining, it really is quite stuck - more than before.
My next attempt will be wiring motor in reverse.


This is an old ex-school lathe. There was a ding on a thread, about 1.5 turns in, that I did my best to file out. Without a jeweller's loupe or microscope to really inspect, it might be jamming, but it didn't feel like it.

If I ever get it off again, I'll ignore visual inspection and try blueing faceplate.



A chopstick/skewer might help cleaning, but in this situation the jaws were binding when taking the job out of the chuck - the chips were working from the hole through the chuck, into the scroll and around under the jaws.