# Locking Threaded Chucks



## David_R8 (Jan 21, 2022)

Thought I'd revive this topic based on some chatter on @YYCHM's threading tool thread (see what I did there?)
The perennial question of how to reverse thread on a lathe with a screw-on chuck.
There's this example








						Southbend 9C Lathe For Sale
					

Why so little? I am almost thinking of shipping it to AB and flipping it for $1650.  Tom, I have to say because I’ve noticed a common trend with you.  It probably won’t go over well being a new member but I can’t imagine this sits well with others.    You want to take a deal being passed on to...




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## David_R8 (Jan 21, 2022)

Model Engineer
					






					www.model-engineer.co.uk


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## David_R8 (Jan 21, 2022)

https://img.photobucket.com/albums/v227/brnstn/Weiler/Weilerchucktightener001.jpg


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## YYCHM (Jan 21, 2022)

David_R8 said:


> Model Engineer
> 
> 
> 
> ...



  Can't picture how that accomplishes anything?


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## David_R8 (Jan 21, 2022)

YYCHM said:


> Can't picture how that accomplishes anything?


I agree, there needs to be some sort of relief cuts in the stub to allow the collar to tighten on the spindle nose.


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## David_R8 (Jan 21, 2022)

A big thread on Hobbymachinist.com








						Locking on a threaded chuck ?
					

Howdy Guys....and Gals if your out there ! ... I have been contemplating the  threaded chuck coming off when using reverse on the motor problem..... ..... I would imagine  a simple screw into the side of the chuck adaptor would cure this problem.... but I've never read where anyone has tried...




					www.hobby-machinist.com


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## Darren (Jan 21, 2022)

I had a threaded spindle on my V10p.  Emco uses a locking collar with 4 relief cuts. It works great, when you remember to tighten the collar.


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## YYCHM (Jan 21, 2022)

dfloen said:


> I had a threaded spindle on my V10p.  Emco uses a locking collar with 4 relief cuts. It works great, when you remember to tighten the collar.



Got a pic?


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## Darren (Jan 21, 2022)

YYCHM said:


> Got a pic?










						Locking on a threaded chuck ?
					

Locking the chuck to the spindle has been discussed before.  Here's one such thread.......  In this reply Bob (@RJSakowski ) shows how his spindle has a groove to lock the chuck on: https://www.hobby-machinist.com/threads/thread-crest-override.40895/post-351007  here, I suggested a draw bar type...




					www.hobby-machinist.com


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## Thomas (Jan 21, 2022)




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## Darren (Jan 21, 2022)

So i had a chuck spin off on me once.

 I was asked to do a quick job.  Shop wasn't heated, was pretty cold, but it was a quick face off to thickness job on a round spacer of some sort. I had to change chucks and neglected to fully tighten the lock ring. When i turned the lathe off at 2000ish rpm, due to the cold and thick headstock oil im guessing,  the 5" chuck left the spindle, dropped onto the lathe bed...and flew right at me. It hit me in the chest, grabbed my sweatshirt, hit my hand as i blocked it, climbed up my sweater, and whacked me in the chin. I caught it before it hit the ground, and then i almost hit the ground. Lathe bed was missing a chunk,, palm of right hand missing a chunk,  and the chuck was damaged beyond repair. Chest hurt like i'd been hit by a truck, palm should have had some stitches.  I'll never own another threaded spindle again.  Be careful if you have one.


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## Tomc938 (Jan 21, 2022)

That must have been a terrifying moment - once you had a chance to figure out what actually happened.


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## Darren (Jan 21, 2022)

Tomc938 said:


> That must have been a terrifying moment - once you had a chance to figure out what actually happened.


It was. It happened very very quickly.

But more than that i felt like an idiot. I know i tightened the clamp, but obviously not enough. I don't even like telling anyone about it, but i think its an important reminder.


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## Tomc938 (Jan 21, 2022)

I can relate.  I will never mention to anyone the times I have left the chuck key in the chuck...depending on RPM, can be a gentle reminder or a hypersonic missile.


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## YYCHM (Jan 21, 2022)

My reverse lockout mechanism....LOL








I did this after watching my chuck unscrew itself one time....  luckily I caught it in time.  I think I was trying to reverse out a stalled drill bit.

The chuck key thing..... well... you probably only do that twice before smartening up.


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## Darren (Jan 21, 2022)

I definetly didn't hit reverse....wasn't possible on that machine, but thats still a good safety measure.


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## Dabbler (Jan 21, 2022)

The brits are famous for their improvised anti-unscrew hacks for their myford screw-on chucks.  Apparently they can indeed safely lock a chuck on. (no endorsement here, though)

@dfloen that was a very close call.


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## Johnwa (Jan 21, 2022)

dfloen said:


> I had a threaded spindle on my V10p.  Emco uses a locking collar with 4 relief cuts. It works great, when you remember to tighten the collar.


The chuck @YYCHM has is an Emco chuck.  The clamping backplate was likely OEM.  There are plenty of images of them on the web.


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## YYCHM (Jan 21, 2022)

Has anyone seen the Emco clamping backplate applied to a 3J?  A 4J you have to dial in anyway you look at it.


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## Darren (Jan 21, 2022)

I had it on the factory 3 and 4 jaw chucks, and one that I made for my 5" Bison set true. The clamp did not change the runout at all.


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## YYCHM (Jan 21, 2022)

dfloen said:


> I had it on the factory 3 and 4 jaw chucks, and one that I made for my 5" Bison set true. The clamp did not change the runout at all.



Which clamp arrangement was this?  I don't have the clamp ring one.  On mine, the slots are cut into the back plate registration with a SHCS to clamp it, no ring.


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## Darren (Jan 21, 2022)

Mine all had separate clamping rings. On the two that I made, I used shaft collars, and bored them to size. The bore was tapered a degree or two to keep it on, the backplate had a matching taper. That way the ring can't fall off unless you really loosen it.


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## YYCHM (Jan 21, 2022)

So, if one had a cast iron back plate could a clamp be made to work?


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## Darren (Jan 21, 2022)

Certainly.  All mine were cast, one was an old pulley, one was a barbell weight.  Ill send a pic of one in the morning


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## 6.5 Fan (Jan 22, 2022)

dfloen said:


> I definetly didn't hit reverse....wasn't possible on that machine, but thats still a good safety measure.


I'm confused, if you didn't hit reverse why did your chuck thread it's self off the spindle?


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## Dabbler (Jan 22, 2022)

6.5 Fan said:


> why did your chuck thread it's self off the spindle?


If your lathe stops abruptly, it works the same as putting it in reverse.  the momentum of hte chuck keeps it spinning, while the spindle is stiopped.  this will unwind the chuck with the result @dfloen  had


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## Darren (Jan 22, 2022)

Dabbler said:


> If your lathe stops abruptly, it works the same as putting it in reverse.  the momentum of hte chuck keeps it spinning, while the spindle is stiopped.  this will unwind the chuck with the result @dfloen  had


thats exactly what happened.


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## DPittman (Jan 22, 2022)

Tomc938 said:


> I can relate.  I will never mention to anyone the times I have left the chuck key in the chuck...depending on RPM, can be a gentle reminder or a hypersonic missile.


These are all good reminders. I do occasionally leave the key in the chuck and kind of shrug it off as no big deal as I have never attempted to turn the machine on....yet.  So I will heed the wisdom  shared here and remind myself to avoid that disaster.


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## 6.5 Fan (Jan 22, 2022)

Dabbler said:


> If your lathe stops abruptly, it works the same as putting it in reverse.  the momentum of hte chuck keeps it spinning, while the spindle is stiopped.  this will unwind the chuck with the result @dfloen  had


Ok that makes sense. Thought it just unwound in forward.


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## Darren (Jan 27, 2022)

Heres one I made :







Thats a shaft collar bored to fit


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## YYCHM (Jan 27, 2022)

dfloen said:


> Heres one I made :
> 
> 
> 
> ...



I have a backplate inbound from @140mower that I'm going to modify to take a shaft collar.  I'll be picking your brain shortly about slotting the threaded portion of the backplate.


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## YYCHM (Feb 11, 2022)

dfloen said:


> Heres one I made :
> 
> 
> 
> ...



Can you repost this image full size please....


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## YYCHM (Feb 12, 2022)

dfloen said:


> Heres one I made :
> 
> 
> 
> ...



I sourced a backplate from @140mower (thanks Don)...






KBC has clamping collars that are very close to the right size.  Is it now just a matter of slotting the flange in 4 spots? How wide should the slots be?  Should I get a one piece or two piece clamping collar?


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## 140mower (Feb 12, 2022)

Hmmmmm, I had a different vision.......
I am thinking of putting one in the bandsaw and cutting it parallel to the backplate to about half way then using a slitting saw with one cut in the middle of the cut section. An allen screw clamps the sections against the spindle. I'll search around and see if I can find a picture of what I am talking about....


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## YYCHM (Feb 12, 2022)

140mower said:


> Hmmmmm, I had a different vision.......
> I am thinking of putting one in the bandsaw and cutting it parallel to the backplate to about half way then using a slitting saw with one cut in the middle of the cut section. An allen screw clamps the sections against the spindle. I'll search around and see if I can find a picture of what I am talking about....



Like this?






It's slotted two ways.


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## 140mower (Feb 12, 2022)

Yup, that is what I was trying to spit out... Lol. It looks like it should lock well and being the cheap bugger that I can be....


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## YYCHM (Feb 12, 2022)

140mower said:


> Yup, that is what I was trying to spit out... Lol. It looks like it should lock well and being the cheap bugger that I can be....



I'm not confident enough to drill the screw hole thought the flange.  The flange pictured is a lot thicker.

Can't seem to get @dfloen to comment on his build?  Blocked me maybe?


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## Darren (Feb 12, 2022)

give me a bit. i'm having internet troubles


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## 140mower (Feb 12, 2022)

YYCHM said:


> I'm not confident enough to drill the screw hole thought the flange.  The flange pictured is a lot thicker.
> 
> Can't seem to get @dfloen to comment on his build?  Blocked me maybe?


Okay, then I would probably put it on my lathe backwards and turn the spigot parallel, then armed with that measurement turn a locking ring as you have in the pictures, drill, tap and split that and cut the back plate as you were going to. But definitely make the locking ring vs buying it, it looks like a good skills building project.


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## YYCHM (Feb 12, 2022)

140mower said:


> Okay, then I would probably put it on my lathe backwards and turn the spigot parallel, then armed with that measurement turn a locking ring as you have in the pictures, drill, tap and split that and cut the back plate as you were going to. But definitely make the locking ring vs buying it, it looks like a good skills building project.



One piece or two piece clamping collar?


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## 140mower (Feb 12, 2022)

I would go with one piece..... This should tell you if you would have hit the center if you did the other method.... Lol 




This is a picture I found on the 'net that shows both methods.


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## YotaBota (Feb 12, 2022)

Would a set screw (brass tipped of course) thru the stub onto the threads affect runout? Much easier than slitting the stub and wouldn't affect the strength of the stub.


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## YYCHM (Feb 12, 2022)

YotaBota said:


> Would a set screw (brass tipped of course) thru the stub onto the threads affect runout? Much easier than slitting the stub and wouldn't affect the strength of the stub.



Some people report that it works, the same people that claim threaded spindles aren't  a problem in the first place LOL.

So far what I call a flange, @140mower calls a spigot and now you are calling it a stub....  What is it?  A boss?


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## 140mower (Feb 12, 2022)

YYCHM said:


> Some people report that it works, the same people that claim threaded spindles aren't  a problem in the first place LOL.
> 
> So far what I call a flange, @140mower calls a spigot and now you are calling it a stub....  What is it?  A boss?


Don't think it is a boss, 'cause it don't look nuthin like the fellow that said we'd be doing as many 12+ hr days as we can stand until the end of March....
 My terminology is probably not so good, my passion for the hobby is much greater than my experience level.


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## YotaBota (Feb 12, 2022)

Pick one LOL, as long as we all know it's the same thing all is good.


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## YYCHM (Feb 12, 2022)

YotaBota said:


> Pick one LOL, as long as we all know it's the same thing all is good.



After looking it up, flange was way out to lunch LOL.  I think boss is right term.


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## Darren (Feb 12, 2022)

Hopefully this shows it better


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## Darren (Feb 12, 2022)

One more


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## YYCHM (Feb 12, 2022)

So it's a pretty wide slit then? 1/16" ?


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## Darren (Feb 12, 2022)

hacksaw blade width


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## Susquatch (Feb 13, 2022)

YYCHM said:


> Like this?
> 
> View attachment 21016
> 
> It's slotted two ways.



I'll be honest, I don't like this. Too easy to crack through and zingoes the front half. And then @ShawnR s moose let's loose. 

ESPECIALLY if it's cast iron!


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## Susquatch (Feb 13, 2022)

After looking at all the photos and discussion and especially the risk, I am inclined to think this needs a rethink. 

For starters, it needs a steel backplate not cast iron. Second, even steel needs a relief hole to reduce stress concentrations. Third, from the photos, the clamping all seems to take place on the unthreaded section of the hub nose (my preferred terminology). I don't like that. I'd prefer a way to tighten the thread grip. Fourth, a brass nosed grub screw might be too easily stripped. 

What a huge dog's breakfast.... 

How about a new adapter between the threaded nose and the chuck? Something that Clamps down on the threaded nose with a vise grip from both sides (front and back) and incorporates a new flange that acts like a backplate. All chucks are then machined to precision fit the new backplate sort of like a D1-X system. I'm envisioning a double collar (like a double nut) to hold the flange to the spindle nose. But I'm not sure there is enough thread there for that. Might need to think about three or four thread wedges instead. 

It's a lot of work but would be MUCH safer! 

It's either that or abandon reverse totally! At least that's what I'd be thinking......


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## RobinHood (Feb 13, 2022)

Susquatch said:


> I don't like this. Too easy to crack through and zingoes the front half.


That was my first reaction when I looked at one of the chucks that came with my 9” Utilathe.

Turns out the chuck was super high quality, made in Japan. The flange bore was a very close fit to the spindle nose flat. The locking collar was made from steel - also a close fit to the flange OD. A single SHCS locked it.

I did some testing: screwed the chuck onto the spindle without bottoming it out against the rear register (about a quarter turn shy, so there was a visible gap). Tightened the locking collar. Took a foot long adjustable spanner and grabbed one of the jaws. Selected highest spindle speed. Blocked the motor by pinching it with wood. Now pulled hard on the spanner. Every time the motor belt slipped. The chuck never spun on the spindle - either forward or backwards. That was proof enough for me that this clamping system works and it is safe to run the lathe in reverse under normal operating conditions.

The close fit of the components, the elasticity of the CI and the strength of the steel collar seem to work well together in this case.

The chuck / collar were exactly like @dfloen has modified his.

@Susquatch , totally agree with the stress concentration point where the saw cuts end. One could try and drill radial holes first and then have the saw cuts end in them. Would go a long way to mitigate the potential… OTOH, the Japanese engineers did not think it was necessary…


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## ShawnR (Feb 13, 2022)

Susquatch said:


> And then @ShawnR s moose let's loose.


I don't get it?


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## Johnwa (Feb 13, 2022)

Cast iron is surprisingly flexible over a short range.  My Ox/Ac instructor asked us whether steel or cast iron was stiffer.  We all thought cast iron.  Then he held out a cast iron and a steel welding rod.  The cast iron drooped like a wet noodle compared to the steel one.


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## Darren (Feb 13, 2022)

The one I made above is made from an old overhead door pulley.thats some tough cast iron. The collar id and the od  where it sits are inversly tapered by a degree or 2 so the collar cannot slide off.  That's just an off the shelf shaft collar from the bearing supply house thats bored to fit.


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## Susquatch (Feb 13, 2022)

ShawnR said:


> I don't get it?


Search on moose......

Just moose. Not sure it was Shawn. But I'm still laughing.


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## Susquatch (Feb 13, 2022)

Johnwa said:


> Cast iron is surprisingly flexible over a short range.  My Ox/Ac instructor asked us whether steel or cast iron was stiffer.  We all thought cast iron.  Then he held out a cast iron and a steel welding rod.  The cast iron drooped like a wet noodle compared to the steel one.



It isn't really whether it's more flexible. It is more brittle. Brittle metal cracks.


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## Susquatch (Feb 13, 2022)

dfloen said:


> The one I made above is made from an old overhead door pulley.thats some tough cast iron. The collar id and the od  where it sits are inversly tapered by a degree or 2 so the collar cannot slide off.  That's just an off the shelf shaft collar from the bearing supply house thats bored to fit.



All good. I'm just being paranoid. I'd be happier with good quality steel. And happier still with a better totally different retention system.


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## Susquatch (Feb 13, 2022)

ShawnR said:


> I don't get it?


It wasn't you, it was @CalgaryPT . Sorry for the mix up.

In my defense, it sounded like your kind of humour.


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## YYCHM (Feb 17, 2022)

Spent the day prepping this backplate that I sourced from @140mower (Thanks Don).....






Had to turn the registration down and re locate/drill the mounting holes.  Then I turned the spigot/boss down to accommodate a 2.25" clamping collar.  Tomorrow I'll source a 1/16" thick slitting saw to slot the spigot/boss with and will see if I can set her up on the mill using a angle plate.  I'm left hand challenged right now and I don't think I can mount the RT due to it's weight.  We will see.

@dfloen will 1/16" be wide enough?  Your images look a lot wider than that.


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## Mcgyver (Feb 17, 2022)

I had a look at the set up on a Schaublin, the clamp is there, but there are not slits in the backing plate just slits in the ring.   That bore is the is the surface that mates with the  shoulder of the spindle is the critical register for the chuck, so not crazy about machining it.  I guess it would depend on how much clearance there was as to whether you had to or not..


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## YYCHM (Feb 17, 2022)

Mcgyver said:


> I had a look at the set up on a Schaublin, the clamping is there, but there are not slits in the backing plate just the ring.
> 
> View attachment 21140



How the heck does that arrangement work?


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## Darren (Feb 17, 2022)

1/16" will be fine. It doesn't need much. It should be tight before you clamp it.


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## Mcgyver (Feb 18, 2022)

YYCHM said:


> How the heck does that arrangement work?



Agreed, its not intuitive, but it works.  I assume the ting tightens up on the plate which should have almost no clearance to spindle and it moves the plate enough to clamp.


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## YYCHM (Feb 18, 2022)

Ha.... don't know why I was thinking RTs and angle plates..... Over thinking things again






Stuck her in the vise and used machinists squares to align things.  Thank god for a PF... it was lots of back and forth and plenty of cutting fluid.  Had the VFD set to 10 hz






Seems to work....  as to how well I won't know until I mount it with a chuck and really reef on it


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## YYCHM (Feb 18, 2022)

She ain't budging.......






Runout isn't bad either,  0.002-0.004 depending upon what you put in the chuck.  This chuck has always run about 0.005.  I think it's the jaws as the chuck body indicates next to zero runout.


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## YYCHM (Apr 9, 2022)

Was doing some turning today that wasn't going well at all......

Discovered the chuck runout had degraded to 10 thou  .  It should have been no more than 5.

Ends up where you tighten the locking ring on the backplate boss can pull things 5 thou out of alignment


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## RobinHood (Apr 9, 2022)

YYCHM said:


> Ends up where you tighten the locking ring on the backplate boss can pull things 5 thou out of alignment


Could be a mismatch of bores/fits somewhere between the critical surfaces. If you have a bit of adjustability on the chuck back plate, you might be able to remove most of it after you install the chuck. Bit of a drag having to do it each time, but might be worth it when you turn more critical parts. OTOH, if you have enough stock for removal, the runout won’t really matter if all the surfaces get machined in one set-up.


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