PDA

View Full Version : Thread mount chuck retainers



Willy
10-16-2008, 11:11 PM
I often read here about the downside of screw mount spindles as it relates to running in reverse. I have no doubt as to what the dubious pleasure of watching a 15 or 25 pound chuck skating off the bench and across the floor at 700 RPM would do for me...I don't have enough clean underwear for that!

My question is if the spindle of a screw mount lathe has the room why don't I see more of this type of chuck retention. I'll be the first to admit though that I haven't seen the spindle of most screw mount lathes. But although this exact type of retention can't always be used, I'm sure a variation of it could be adapted to most lathes with treaded spindles. Or are the spindles too short for any kind of retainer?


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

macona
10-17-2008, 12:10 AM
On a lot of the threaded spindle I have seen there is maybe 1/8 to 1/4 max sticking out before the register.

What Emco does is split the area by the thread register like a split collar clamp. Tighten it after you spin the chuck on and you are good to go. I bet that would also keep the chuck from overtighten itself.

I have had chucks come off on me before. I was turning some flywheels for a little hit-and-miss on the old Artisan. Problem with that Artisan is it stops NOW when you pull in the clutch. It didnt that time! Well, the spindle did but not the chuck. Luckily the spokes caught in the tool holder and everything came to a quick stop.

DickDastardly40
10-17-2008, 02:32 AM
The spindle on my older style Myford is too short for a retainer. If I'm gonna have to reverse the spindle, I try to support the job with with the tailstock which I find keeps the chuck where it's supposed to be. If not try I try to keep the speed down to prevent inertia when the spindle stops and the chuck doesn't!

Duffy
10-17-2008, 11:47 PM
Assuming that the backplate has a "neck" of some diameter much smaller than the chuck itself, why not drill and tap for one or more set screws, (with brass pads?) It is my understanding that two set screws 90 or 120 degrees apart will provide enough resistance to overcome the inertia of the chuck.

Don Young
10-19-2008, 11:08 PM
I have a dog driver plate which is drilled thru from the rim for a setscrew. It goes into the threads and I assume there was a soft plug in it to prevent marring the threads. It looks like a South Bend plate and the hole looks factory made but I do not know for sure.

If you do not need the spindle hole, a long bolt and a suitable washer behind the chuck jaws should make a good retainer.

Don Young

Fasttrack
10-19-2008, 11:16 PM
On a related note, my brother-in-law had a chuck come off of a L1 mount the other day. It was running in forward but the collar must not have been tightened all the way so it worked its way loose and the chuck slipped off the taper. Scary since the chuck weighs a bunch (it was a Bison 8" 3 jaw). Luckily the work piece was supported by a center in the tailstock so the chuck didn't come completely off the spindle. Still not entirely sure how it happened...

pipeclay
10-20-2008, 05:31 AM
On a related note, my brother-in-law had a chuck come off of a L1 mount the other day. It was running in forward but the collar must not have been tightened all the way so it worked its way loose and the chuck slipped off the taper. Scary since the chuck weighs a bunch (it was a Bison 8" 3 jaw). Luckily the work piece was supported by a center in the tailstock so the chuck didn't come completely off the spindle. Still not entirely sure how it happened...

Was the Lathe running in reverse or was the mounting plate left handed,Im no expert but it would appear to me the only way you would possibly run the chance of loseing a 3 jaw chuck with right hand thread through carelessness.especially seeing that it was being turned between centres,I would think that if It was a Right hand thread that the operator requires a refresser in mounting jobs in the lathe,and I would be suggesting a refressher in the mounting of all work pieces.

oldtiffie
10-20-2008, 06:01 AM
I haven't used a screw-on chuck for more years than I want to remember. I do recall that thread and mating part cleanliness was paramount.

We used to screw the chuck on by hand until it was just "snug" or touching, then we would engage a low gear or back-gear and "back it off" by (by hand) for 1/4>1/3 of a turn and then spin it on sharply and make sure it did not "bounce". We rarely had one come off.

We also had/made very solid "C" spanners that fitted into the square chuck key holes and used either a solid phosphor-bronze "dolly" or a "dead hammer" on the "C" spanner to tighten or loosen the chuck as required.

I prefer the simple but very effective spigoted bolt-on flange that I have on my Chinese lathe. In the unlikely event that it loosens (it never has), I will get ample warning.

There is a huge amount of inertia and potential energy in a spinning chuck, which ideally should be slowed gradually. Spindle braking and screw-mounted chucks are a potential risk.

mark61
10-20-2008, 06:52 AM
I had the same thing happen to me with a 16" 4 jaw chuck on an American lathe. Spindle can not be reversed. I think the mount does have right hand threads looking at the back of the chuck. Only happened once right after I got the machine. Probably over tightened it when I put it back on. Used a 3 lbs. hammer and chunk of brass to "snug it up". Will check the spare chucks next time I go to the shop see about the thread direction.

mark61

Scishopguy
10-20-2008, 03:14 PM
I had two Sheldons in the university shop that I worked in that had threaded spindles. As Old Tiffie said, cleanliness was important. The back plate on the chuck tightened up against a flat on the spindle and we would smartly spin the chuck that last quarter turn until it engaged the flat. I only had a chuck come loose once. It was on the older (WWII shipboard lathe) when I reversed the spindle. It didn't come all the way off but did start to wobble. It was a 10" Rohm with reversible jaw that weighed about 30 or 40lbs so it would have been a bad scene if it had fallen off. From the look of the ways on that machine it had happened before. I learned not to instant reverse a threaded spindle that day. ;) even when you are power tapping at low speed.