View Full Version : Pratt burnerd setrite chuck problem?

10-28-2012, 02:38 AM
I just received a Monarch ee back from Monarch lathe company that had the bed reground, and and a few other minor tuneups. I am in the process of fitting a backplate to a new 6" PB setrite chuck. I mounted the plate on the d1-3 spindle (less than .0001 spindle runout) then faced the plate to .0001 TIR. I took a skim cut across the back plate hub to allow for .012" clearance when mounted to the chuck when using the setrite feature. I mounted the chuck to the plate and clamped a 1/2" precision dowell pin. I indicated the pin to .0001"/.0002" at 1/4" from the jaws. I was getting a TIR of .002" at 1.5" from the jaws. My question is.......Is this normal to see that much TIR on such a short distance from the jaws?.......I then put in a 8" piece of 3/4" steel round that I cut true between centers on my old lathe. I check the runout at the jaw face and had .002" and at 6" it was .009". This seems like too much run out for a new 3 jaw chuck. I then checked the the perimeter of the chuck and had .007" TIR ...I didn't like that chuck turning that much out of balance either. Any thoughts of where I should start checking to see if I can true things up a bit or am I expecting too much out of a three jaw chuck.......any help would be appreciated.


Forrest Addy
10-28-2012, 02:50 AM
Yup. There are two kinds of runout: eccentric and angular. Eccentric runout can be corrected by adjustment of the off-setting screws in an adjustable three jaw chuck.

The top quality adjustible chucks may have some angular run out even when new and in perfect shape. Angular runout is a product of unequal jaw splay which itself is a product of manufacturing tolerance and subsequent wear and deformation from wrecks. It's very difficult to ensure zero angular runout because there is no angular adjustment. If the ends of the jaws can be restrained for internal grinding the inevitable angular error can be greatly reduced.

10-28-2012, 03:03 AM
Could it be that the back face of the chuck (the part that touches the backplate) is not perpendicular to the jaws? To check, true up a bar between centres, clamp on the chuck with the jaws facing the headstock and check runout at the back.

10-28-2012, 06:01 AM
Is it possible that the head-stock spindle has a bend in it?

For that sort of accuracy I'd opt for "soft jaws".

10-28-2012, 08:49 AM
My original assessment was some sort of angular runout. I going to borrow my friends monarch ee precision test bar and check ou the alignment of spindle to the bed. Anyway to check the alignment of the spindle face to the bed?......I,m hoping just a chuck problem. I never thought about checking the back of the chuck.


J Tiers
10-28-2012, 09:55 AM
Why are you worried about the spindle? misalignment will cause taper, and coning of faces, but not runout.

You already faced the plate to 0.0001" per your first post. That should take care of any possible problems of spindle straightness, unless you removed and re-attached the part, setting it in a different position.

Did you reference the correct part of the chuck?

Part of the surface is likely ground true, the rest may or may not be good. On my chucks, it is the rim, and the backplate is a "top hat" shape, with the chuck sitting on the "hat brim" around the back surface.

Check the face runout of the chuck. Any decent chuck maker will have ground the chuck true, and the face will be perpendicular to the axis and parallel to reference surface.

if the face runout is good, but the test pin runout is bad, the problem is likely in the jaws, or possibly due to grit holding your pin askew.

If the chuck face does rin "out", then check the face runout of the backplate. If good, look for grit in between chuck and plate, or use of the wrong reference surface.
If bad, check seating of the plate on the spindle taper, and check the taper for grit etc.

If the spindle face is true and the taper surface is true, the spindle itself is probably not a problem.

Rich Carlstedt
10-28-2012, 11:28 AM
New Chuck ? ------Call the manufacturer !
First, brand new , it should not have .007 TIR on the body ( realizing that you may have moved it there to center on the pin)
Second, there are replace-able jaws (soft ?) on the Setrite Chuck. Were the jaws moived ? Is there dirt under the jaw seat ?
Third, if soft jaws, then the body should be adjusted to .0000", and the jaws bored in place .
Call Pratt Burnard first
(269) 384-2225


10-28-2012, 12:39 PM
Thanks for the phone # Rich..........I checked the face on the chuck and there was Virtually no detectable runout, less than 2-3 tenths. Spindle and spindle face show about .0001" TIR or less. I pulled the jaws off to take a look and I remembered when I got the chuck in June that I put some grease on the jaws.......Dumb move!.. what was I thinking.......I am going to clean up the Jaws and center the chuck and see what happens. I have a feeling that I created my own problem w/ a rookie mistake as PB recomends not to put anything an the jaws. I'm going to center up the chuck w/ the setrite and put a pin in and see what the results are. I'm hoping I have a chuck problem and not a lathe problem. I'll put the Monarch ee test bar in when I pull the chuck off to clean it up. Thanks again!


10-28-2012, 12:48 PM
I've seen runout walk with the pins and the cams, so I always mark a chuck with the cam numbers so it alwaus goes back in the same position as where I faced it. After that I start working my way out from the backplate face by seeing how bluing transfers from the backplate to the back of the chuck - you should see a nice even transfer. If that's OK then I check the taper on the chuck to make sure that it's on center. If everything else is right but you're still getting some nonaxial indication I'd check that it wasn't in just one of the collets by trying several collets, making sure that it wasn't just one of them. If it wasn't then I'd consider regrinding the chuck in place, likelt very little would have to come off and the EC has a pretty sharp taper so you won't have the problem of setback that shows in morse taper and such.

I'll be mounting a KC-15 on my 10EE in the next couple of weeks, feel free to PM me your email and maybe we can trade notes. I've mounted a few chucks but this will be my first KC-15.

(Edit: heck, if it's new and you can show it's not the lathe send it back and let the manufacturer sort it out. I'm more used to fitting used chucks and always just go to the "make it work" point of the process.)

Rich Carlstedt
10-28-2012, 04:15 PM
Do the replacable jaws have numbers ?
They must match the jaw socket numbers !
You mentioned grease, but I am concerned that they went back into the wrong jaw socket


10-28-2012, 10:14 PM
I finally got home to play with the lathe. The jaws are numbered and match the numbers on the chuck. I cleaned out the chuck and it is spotless. Set up the chuck the same. Same results as before. I put in the new monarch ee test bar from miller machine and vertical and horizontal test over 12" showed a TIR of ..0002-.0005" vertically and horizontally over the length of the bar without support and with support from a center in the tailstock. So the lathe checks out great. What about the back plate. I took the back plate off and tried the pins in all 3 different ways. I don't think the taper on the backplate matches up very well w/ the spindle. On the rear flange that fits on top of the spindle is .007" out of round every way i had the pins mounted and the rear face of the back plate doesn't turn very true. My chuck was .007" TIR when mounted on the plate after facing and dialing in a 1/2" pin. Seems odd. When I centered the chuck and put in a 1" test bar I was .020" TIR at 5"...not good. I don' know what else to try. I' call PB tomorrow and see what they say. I'm about ready to throw the chuck out the door. Any suggestions?


10-29-2012, 11:28 AM
The chuck is going back to Pratt Burnerd. They suggested to send the chuck back and they will regrind the jaws. There suggested method is to center the chuck to .001" or less and true up the jaws with a grinder. Thanks for all the help!


Tim in D
10-29-2012, 12:20 PM
Did you blue the taper and backplane of your mounting plate to your spindle nose. Could be that the backplate doesn't register repeatably on the spindle nose...........

Just sayin......

Tim in D

10-29-2012, 01:09 PM
No I never blued the backplate taper. I thought about doing that before I send the chuck back. I may do that tonight just for grins. It appears to mount repeatably when I align the same pins to the spindle.


Tim in D
10-29-2012, 02:33 PM
I think you will find it to be an interesting exercise. You will see any dings on the taper nose and you will know just where the chuck plate is contacting the spindle. Don't use too much blue. Also, check the JT inside. Mine had a bunch of high spots on it (both inside and out). The nose is real soft and a chip between the chuck mount and taper will pull up a burr.

Re your dead center.................pick up a Jarno dead center and use it directly in the spindle without any adapters. (be sure to scrape it in)

Tim in D

12-21-2012, 08:00 PM
Just got the chuck back from PB last week. The regrind of the jaws came out great. The chuck repeats as good as any chuck I've ever used. After dialing in a precision gauge pin to zero TIR anytime I take the pin out and re-chuck the pin the TIR has been no greater than .0003" at that same location. The angular runout is no longer evident further out from the chuck. Customer service at PB was great - they picked up the freight bill both ways. Thanks PB. I'm a happy camper. Thanks for all the help


Rich Carlstedt
12-21-2012, 10:31 PM
Glad to hear they took care of the problem. They have always been a good chuck manufacturer and this proves that they
want to continue their fine tradition. I have a 6 " 3 jaw that is just superb

Krems, I forgot if they have 1 or 3 adjustment sockets on the Setrite ?
If 3, then you need to retest the runout, tightening only one socket..each test.
You will find the " master" socket that was used when they ground the jaws... insitu .
Mark the other 2 with red paint and never use them.
My recollection is they have only 1...so no problem