Incorrect lathe chuck removal

Jaydee · Mar 3, 2021

I have a Harrison L5 Lathe with a 1.5” Threaded spindle

For a number of years I have been unscrewing the chuck by putting the lathe in bottom gear and using the chuck key. I have had to use a mallet on a few occasions when the chuck was tight.

I have now been shown a better way to remove the chuck without using the chuck key!

But my question is have I done any damage to the chuck, would this compromise the chuck body?

The chuck is a non-branded Chinese type 5” 3 jaw and a old Pratt 8" 4 Jaw which I presume are both cast steel

Just a Sparky · Mar 3, 2021

Biggest thing I'd be worried about is shearing the gear teeth unless they've been case hardened. Hard to do with just upper body strength, but throw in a hammer...

M.B. Naegle · Mar 3, 2021

I think the risk of improperly tightening or loosening a chuck from the spindle really depends on the lathe. I doubt much damage would be done to the chuck unless you were hammering on it, but I'd be more concerned about the risk of damaging your back gears.

IMHO, on a tool-room type cone head back-gear lathe, using the back gear to hold the spindle from moving is ok, provided you don't hammer the chuck tight/loose. We keep a 12" length of hardwood handy to loosen chucks on our South Bend Heavy 10 by putting it between the jaws and pulling while the back gear is set. It's never given issue, but if it was ever so tight that I needed to grab a hammer or something, I'd rather keep the gears out of it and use a different method. Similarly, I only hand tighten chucks with no leverage. It self tightens when running forward and I've never had one come off in reverse.

Illinoyance · Mar 3, 2021

Using the chuck key to turn the chuck can result in a split socket on the pinion.

Jaydee · Mar 3, 2021

M.B. Naegle said:
I think the risk of improperly tightening or loosening a chuck from the spindle really depends on the lathe. I doubt much damage would be done to the chuck unless you were hammering on it, but I'd be more concerned about the risk of damaging your back gears.

IMHO, on a tool-room type cone head back-gear lathe, using the back gear to hold the spindle from moving is ok, provided you don't hammer the chuck tight/loose. We keep a 12" length of hardwood handy to loosen chucks on our South Bend Heavy 10 by putting it between the jaws and pulling while the back gear is set. It's never given issue, but if it was ever so tight that I needed to grab a hammer or something, I'd rather keep the gears out of it and use a different method. Similarly, I only hand tighten chucks with no leverage. It self tightens when running forward and I've never had one come off in reverse.

Hi

That's the method I'm going to use from now on

I’ve never over tightened the chuck when fitting, and always kept the spindle thread clean & oiled

But a few times it has gone very tight after some heavy machining, I’ve checked the gears within the headstock and all seems fine, its the chuck I was most worried about!

Dan from Oakland · Mar 3, 2021

Always good practice to use a block under a chuck jaw or make a flat wrench that has slots to fit over the jaws. Banging on the wrench is hard on the gear teeth- better approach is low gear and rotate the drive pulley backwards by hand, although on newer machines that would be a PITA.

neanderthal mach · Mar 3, 2021

It seems to be a method that was once much more used in the UK than elsewhere, but one tip I picked up from an old Model Engineer magazine was to cut out a thin cardboard washer that fit's between the spindle register face and the mating face on the chucks back plate. Soak it in light oil. Paper and cardboard are remarkably consistent in thickness so you should still see the same run out on the chuck face. The oil soaked cardboard prevents it from picking up moisture from the air and causing rust. And the thin cardboard compresses slightly as the chuck tightens in use, but still prevents that zero clearance metal to metal contact. I no longer have any lathe with a threaded spindle, but when I did the chucks were a whole lot easier to get off with that simple trick.

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Incorrect lathe chuck removal

Jaydee

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Just a Sparky

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M.B. Naegle

Diamond

Illinoyance

Stainless

Jaydee

Plastic

Dan from Oakland

Titanium

neanderthal mach

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