# "HELP" with Lathe Speed Chuck



## Sandia (Jun 9, 2013)

Okay, I just purchased a ATS-Sjogren Speed chuck for my lathe with a D1-4 mount. When I fit it up to the spindle on my lathe is does not fit flush up against the flat spindle face. When you tighten the pins you can still see light between the chuck and the spindle at one spot are another depending on how you tighten the pins or what sequence. The runout varies between .005 to .010 and occasionaly you get lucky and it will be around .002. It appears to me the the taper in the chuck is too large for the spindle mount. When you hold it in place before locking it down you can rock it slightly in place. The lock pins are adjusted correctly and I have tried indexing the chuck in a complete circle several times but no luck. My question is, can you turn a little off the OD of the taper on the chuck or how do you guys correct this problem??? Any suggestions please !!! 
:thinking:


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## Codered741 (Jun 9, 2013)

First things first.  Measure the OD of the taper to verify your hypothesis.  Check all of the dimensions that you are able to, on both the spindle of your lathe, and the chuck.  If all the dimensions match, then you have a different problem.  

You can find the dimensions for a D1-4 chuck mount here.  

If your measurements do not match, did you just purchase the chuck new?  If so, I would contact the manufacturer, and see what they say.  

Of course it is possible to skim the taper in the mount of the chuck, though there are several challenges to this.  The first one is of course, holding the backplate to machine the taper.  I would say that a faceplate would be your best bet.  

The second problem that you may face is that the taper may be hardened.  This would then require special tooling to machine it hard, a toolpost grinder would be easiest and most accurate, IMHO.  

And last but not least, matching the taper angle.  Shouldn't be too difficult, but will need to be done precisely.  

But if you just bought it new, I would contact the manufacturer for a replacement, after checking the dimensions on both the chuck and your spindle.


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## British Steel (Jun 9, 2013)

First off, how much daylight are you seeing between chuck and spindle nose? A.couple of thou" or a few tens of thou"? If just a couple, check the mating surfaces for any nicks, raised dings or burrs (including around the camlock studs and cam sockets: gently stone off (or use a bearing scraper if on the internal taper) any you find and retest, the smallest of burrs etc. (particularly on the tapered surfaces) will cause runout and prevent the chuck seating correctly.

If, once any damage is cleaned up, the chuck still won't seat correctly, either the chuck's taper or the spindle nose could be out of spec, assuming other D1-4 chucks fit it sounds like the problem is with the chuck's. Tricky.

You'll need to make a dummy taper matching the spindle nose in a soft material (brass or aluminium) to use as a lap - it's ok if it's slightly "longer" than the taper on the spindle, that face needs clearance. Mount the lap on a shaft or taper so you can hold it.with the tailstock, check it's concentric, very accurately!

You'll need a precision ground bar, either in a native collet or a 4-jaw, centred very accurately that you can grip in the Sjogren with it reversed to get access to the taper - check it's running true within your specified limitsc then comes the scary part - applying the lap and fine abrasive, rechecking often for the correct clearance, a few thou", between the flat faces of the chuck and spindle.nose - there should be some.clearance, the D1-4 taper is.meant.to be a light interference fit and the camlock closes up the clearance. Bear in mind that the taper's fairly shallow so a few tenths of.a thou) off the taper will take a few thou" off the clearance, go slowly and gently!


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## Ray C (Jun 9, 2013)

Here's a thread that covers this issue...  This is a common problem.  Seems most chuck backs are made undersized -I guess once a hole is too big, it tends to stay that way...  Not sure if your chuck has a built-in back or if it's two pieces (chuck + backplate).  If it's integrated, I'd be inclined to talk to the manufacturer/distributor because, the D1-x specs are widely published.  Just be on the safe side, measure your spindle dimensions to make sure there's not problem there.

http://www.hobby-machinist.com/showthread.php/10651-D1-4-Spindle-amp-Chuck-Measurement-and-Setup

Also, make sure the lugs are straight and length set properly. If one or more are cocked, the chuck might not be going in all the way -same thing if one or more are too long.

Ray


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## British Steel (Jun 9, 2013)

Good thread, Ray, but... If you look at a reputable chuck manufacturer's documentation, the unloaded gap between chuck / backplate and spindle face is part of the spec - the taper is to be pulled into an interference fit by the force from the camlock action, the flat faces won't (or shouldn't) touch until the cams are locked.

The taper is the critical fit for concentricity and repeatability, the flat faces are to maintain an even force pulling the tapers together, hence the clearance to be taken up. If I remember right, it should be around 5 thou" with the chuck pressed on the taper by hand, closing up to zero on tightening - the zero test I've always used is whether strips of finest-weight cigarette paper (about three tenths) mid-way between the studs are gripped when the cams are rotated to the locked (90 - 180 degree) position.


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## Ray C (Jun 9, 2013)

Indeed, but I sure got tired of the chuck getting cocked every time I had to swap chucks (which is quite often since I have one lathe and many jobs going on at one time -thus, I swap the job out by taking off the chuck.  I have about a dozen chucks.).  Ever since I did this, my chucks zero first time, every time.  It's a laborious process to set it up right for the cut and in retrospect, I should have made a "mock spindle" to do a test fit and sneak-up on the right size.

The process works for me and the lathe is almost 2 years old.

EDIT:  On the last couple backplates I purchased, I would need a crowbar on the end of the key to crank it tight enough for the faces to fit...

Ray




British Steel said:


> Good thread, Ray, but... If you look at a reputable chuck manufacturer's documentation, the unloaded gap between chuck / backplate and spindle face is part of the spec - the taper is to be pulled into an interference fit by the force from the camlock action, the flat faces won't (or shouldn't) touch until the cams are locked.
> 
> The taper is the critical fit for concentricity and repeatability, the flat faces are to maintain an even force pulling the tapers together, hence the clearance to be taken up. If I remember right, it should be around 5 thou" with the chuck pressed on the taper by hand, closing up to zero on tightening - the zero test I've always used is whether strips of finest-weight cigarette paper (about three tenths) mid-way between the studs are gripped when the cams are rotated to the locked (90 - 180 degree) position.


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## Sandia (Jun 9, 2013)

Wow, thanks fellows for all the feed back, especially so quick. I will work on it tomorrow and check the dimensions as you mentioned. My 3 jaw and 4 jaw seat perfectly which leads me to believe the problem is with the chuck backing plate. I purchased it off Ebay and it is in prestine condition, anyway we will see. I will report back my findings.

Thanks


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## British Steel (Jun 9, 2013)

I found the two original Pratt-Burnerd chucks that came with my lathe (with the serial number stamped on 'em) zeroed nicely, not bad for older'n me (it's 58 this year!) but new D1-5 backplates are pretty random, and as I've added a few more chucks (5c, ER, smaller 4-jaw's) and a few faceplates I've had to lap the tapers and face the flats for a good fit - always with a few thou" clearance, and a firm hand on the key 

As for far-eastern import lathes and chucks, some are good out of the box, some haven't a hope in hell of fitting without a lot of.work... Having worked at an importer, I have quite a few on which to base that opinion!


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## Ray C (Jun 9, 2013)

Pratt is a good chuck.  My father had them (and he actually knew what he was doing .  Seriously though, the new backplates these days are crazy.  Haven't seen one yet that's actually flat so, I always surface grind them as the 1st step.

I very much agree with you.  It should be a slight interference fit but...  a friend asked me to mount a couple backplates and the space between the faces was probably well over a 1/16" on his lathe!  My eyes nearly popped-out when I came over to take a look.  His spindle dims were dead-on. -That's a little more than an interference fit and it seems to be how they all come now. 

Ray




British Steel said:


> I found the two original Pratt-Burnerd chucks that came with my lathe (with the serial number stamped on 'em) zeroed nicely, not bad for older'n me (it's 58 this year!) but new D1-5 bacplates are pretty random, and as I've added a few more chucks (5c, ER, smaller 4-jaw's) and a few faceplates I've had to lap the tapers and face the flats for a good fit - always with a few thou" clearance, and a firm hand on the key


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## Sandia (Jun 9, 2013)

Ray C said:


> Here's a thread that covers this issue... This is a common problem. Seems most chuck backs are made undersized -I guess once a hole is too big, it tends to stay that way... Not sure if your chuck has a built-in back or if it's two pieces (chuck + backplate). If it's integrated, I'd be inclined to talk to the manufacturer/distributor because, the D1-x specs are widely published. Just be on the safe side, measure your spindle dimensions to make sure there's not problem there.
> 
> http://www.hobby-machinist.com/showthread.php/10651-D1-4-Spindle-amp-Chuck-Measurement-and-Setup
> 
> ...


Thanks Ray, I found this thread after I posted, guess I overlooked it in my search. Good article for sure.


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