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Duffy
06-20-2010, 05:43 PM
I have a Logan with a threaded spindle, and I am sure that a lot of people have lathes with this type of spindle. Everone is warned about taking care when operating in reverse, the general idea being light cuts are (hopefully) OK.
I did not know any better, so I tapped the shoulder of the chuck backplate in two spots 90* apart, 3/8"-16. I installed two brass-tipped set screws. According to a suggestion for mounting pulleys, this is supposed to ensure no slippage. The brass tips cause no damage to the spindle threads, and everything seems to work fine.
Is this one of those light bulb moments that everbody else ALREADY does, or is it a good idea? What say you?

J Tiers
06-20-2010, 09:11 PM
I would class it, for myself, as one of the ideas I have had, but decided not to do.

My reasoning was that it is not "positive" restraint like a key, and would probably "let go" at the most inopportune moment, after I had got thoroughly used to relying on it.

I have 'got away with" a lot of reverse rotation stuff that should have been a problem. And, I have also had the chuck effortlessly unwind as if it were on ball bearings..... with barely a cat's whisker worth of cut.

I am not sure I would trust a friction-only restraint. Actually, I am certain I WOULD trust it, but not at all certain how FAR I would trust it.

Dr Stan
06-20-2010, 11:35 PM
To ensure a positive lock one would need to drill a hole part way into the spindle threads aligned with the set screw. Since each chuck will have a different thread start, one would end up with a lot of holes in the spindle. :eek:

Blackadder
06-21-2010, 02:40 AM
then do as Myford do put a groove in the spindle and use a ball end grub screw

its not running in reverse its running normally when the spindle stops a bit quick the chuck is still going and unscrews


BTW mine tops out at 3000 rpm ,no mods they are like that from the factory

Stuart

Astronowanabe
06-21-2010, 02:41 AM
then how about a shallow groove?
On mine there is only about 3/16 to work with, before the threads,
maybe an 1/8 vee groove 1/16 from the shoulder on the spindle.

seems that would be too wimpy a set screw

J Tiers
06-21-2010, 08:22 AM
To ensure a positive lock one would need to drill a hole part way into the spindle threads aligned with the set screw. Since each chuck with have a different thread start, one would end up with a lot of holes in the spindle.

So what?

That's the point...... it's not super-practical, and you forgot to mention that it would change with wear, although that would hopefully be slow and not a severe issue.

Dr Stan
06-21-2010, 10:32 AM
So what?

That's the point...... it's not super-practical, and you forgot to mention that it would change with wear, although that would hopefully be slow and not a severe issue.

That is my point. While it could be done form an engineering point of view, it is highly impractical.

Willy
06-21-2010, 10:54 AM
As J Tiers suggested it would probably suffice for most situations and build up a trust in a mechanism that is not positive. It could possibly work for years without a hitch, but it still has the potential to let go when least expected.

Still used sparingly and with discretion it is head and shoulders above what you had before.

This is a very positive solution.
The key requirement here is one of sufficient spindle length in order to accommodate the groove in the spindle.

http://i76.photobucket.com/albums/j31/250willy/chuckmount.jpg

garyphansen
06-21-2010, 11:10 AM
It a live center is used when running the lathe reverse the chuck can not unscrew. I have put many miles on my lathes with threaded spindles in reverse and have never had a chuck unscrew. Gary P. Hansen

moe1942
06-21-2010, 11:34 AM
Drop a ball of lead shot of the right size in each set screw hole and the set screws can be tightened down sufficiently to prevent chuck movement and will not damage the spindle threads.

Black_Moons
06-21-2010, 11:53 AM
Iv heard of screw on chucks with 'clamps' that clamp onto the spindle, Seems like an OK solution. I assumed it was something like a split circular clamp. Willys picture is nifty too.


How about something more extreme, Like a drawtube for your chuck that has left hand threads to tighten it and goes all the way through the spindle? :)

Of course, thats gonna steal some of your spindle bore, but it could be removed whenever you need spindle bore more then lathe reversal.

Dr Stan
06-21-2010, 12:27 PM
I think Willy's solution is the best one I've seen.

BTW, I've seen chucks unscrew.