Four jaw chuck runout

JonathanK

JonathanK

New member
I have an Import 4 jaw chuck that came with my lathe, when I dial in work with the indicator close to the chuck I get runout when I move my indicator out from the chuck(.001 .002 TIR when indicating 3 inches from the chuck. I isolated the high spot to being one of the jaws, when I move that jaw to a different position the high spot would follow. I decided to true the jaws to the axis of the machine with a boring bar and I have a plan that I think will work. I pushed a piece of 1.5" stock in to the spindle to where only the back .200 of the jaw are gripping it, I then dialed in the chuck using a DTI on the inside of the jaws. Next I ran the DTI inward towards the spindle to make sure I wasnt binding the jaws by only gripping with the very back portion. This setup keeps a load on all 4 jaws and allows me access to bore the jaws, I could later grind the .200 below my boring. This seems to require a very rigid setup as it is hardened steel and interupted cuts. I know the chuck is cheap and I have a good 3 jaw 6" Set-Tru on the way, but I still want to see if I can make this one work the way it should. I was wondering if anyone else has came across this issue and how they fixed it. Also advice on cutting this interupted hardened material would be great.
Thanks
Jonathan K
 
I've attached and image of a tool that allows loading of three jaws leaving gripping surfaces clear for truing. You could do something similar for a four jaw.

lathe chuck tru tool.jpg

zp3
 
Johnathan, you are trying to make a silk purse out of a sows ear. Chuck jaw truing is a B**** and you need a special setup AND can get hurt or damage your lathe if not extremely careful.
 
I`ve been assoc. with chucks/lathes/mills/grinders etc. a long time...... made a living at it .... do my own barrel work have a lathe in workshop.
I unpacked/cleaned (new ) and mounted a few.buck chucks/cholchesters/warner-swaysys....I have never seen one that would hold a test bar straight.Too many fits,bearing slop,thread slop,jaw fit... etc.etc. leading up to final indicator reading.
Have seen hard jaws ground... waste of time.You either gotta turn a set of soft jaws ( 3 jaws )... or work around the handicap in other ways.... that`s where expeirience comes in....not taught in books... too many variables.....
bill larson
 
bill larson said:
I`ve been assoc. with chucks/lathes/mills/grinders etc. a long time...... made a living at it .... do my own barrel work have a lathe in workshop.
I unpacked/cleaned (new ) and mounted a few.buck chucks/cholchesters/warner-swaysys....I have never seen one that would hold a test bar straight.Too many fits,bearing slop,thread slop,jaw fit... etc.etc. leading up to final indicator reading.
Have seen hard jaws ground... waste of time.You either gotta turn a set of soft jaws ( 3 jaws )... or work around the handicap in other ways.... that`s where expeirience comes in....not taught in books... too many variables.....
bill larson
Click to expand...
Bill, did you by chance work for Regal Tool?
 
No Jerry I did`nt work there..... but I know many who did/do..... my hunting buddy is the maint. sup.They were bought out by the Koreans several years ago and cleaned house after 40 years....threw/scrapped out scads of good/new... tooling/machines..... guess where it`s at now...??? The plant sits 1/2 mile south of me....
bill larson
 
I've trued several chucks by using a tool post grinder. I can't imagine the beating the interrupted cut on hardened jaws would create. The key to good results is loading the jaws and as long as they are relatively tight in their keyways (and scroll on a 3 jaw is decent) it is worth doing IMO. I've clamped down on something like you describe, but you end up losing some jaw length and you can't run the stone past it. The last couple I did I clamped on a piece of ground stock the diameter I needed then ran a thick bead of rtv down both sides of each jaw. Let the RTV fully set then loosen the chuck, remove the ground stock, and then tighten the jaws to put the RTV in a good amount of tension. That will keep the jaw engaged back against the scroll or adjusting screw. I rescued a nice 9" Buck adjust tru that had been ground with the chuck body off center, an older cushman, and a no name four jaw that acted like the one described. All came out with less than .002" runout on multiple diameters for the three jaws and pretty much dead nutz on the four jaw. Grinding takes a while but the results are worth it. Make sure to let it spark out and vary the infeed so you do it both with the stone outside as well as in past the jaws to compensate for any stone wear. If grinding is not an option, then soft jaws are probably the next best bet.
 
A tool post grinder would be ideal, but not an option at this point. The reason I want true jaws is for dialing in fixtures (action, bolt truing ) with as least runout as possible.
 
we`re all talking the same relative thing here.... but when I say running true.... I mean 12" out from the chuck..... imagine this.... hold a pencil in the middle between 2 fingers..... rotate it..... the section of the pencil held at fingers is running true...... but either end can be running out alot....
Now then.... imagine chucking up a straight 30" barrel in the middle......15" sticking out on each side of the chuck.... indicator at the chuck reads "0"...what does each end read.....???... it`s at the mercy of spindle joints,and spindle bearing slop.
bill larson
 
Don't!

bill larson said:
we`re all talking the same relative thing here.... but when I say running true.... I mean 12" out from the chuck..... imagine this.... hold a pencil in the middle between 2 fingers..... rotate it..... the section of the pencil held at fingers is running true...... but either end can be running out alot....
Now then.... imagine chucking up a straight 30" barrel in the middle......15" sticking out on each side of the chuck.... indicator at the chuck reads "0"...what does each end read.....???... it`s at the mercy of spindle joints,and spindle bearing slop.
bill larson
Click to expand...

Bill and Jerry have given you very good advice. If you try to bore the hardened chuck jaws, you have a good chance of a disaster...ruining your lathe and/or injuring yourself.

The right way to do this is with a tool post grinder, and it's a very tricky job to do it right.

Unfortunately there is no such thing as a good imported (Asian) chuck...or much other tooling for that matter. I think the best you could do is to bore a set of soft jaws for your imported chuck.

Greg Walley
Kelbly's Inc.
 
Good Lord, it's a four jaw chuck. You can work with that thing untill you are blue in the face, and to expect it to chuck up a piece absolutly true, time and again, in the manner that you described is being totally unrealistic. There are simply too many variables.

As for cutting that interrupted hardenned material, you are probably getting ready to make a big mess. Just leave it alone and figure out a way to chuck the piece so that the bind in the chuck jaws becomes a non issue.

Exactly what are you making? Maybe we can give you some tips on how to chuck something up dead true in a 4-jaw........jackie
 
The issue I have is dialing in jigs, fixtures, and mandrels that are premade(action truing mandrels, bolt knob jigs etc.) due to runout as I indicate further from the chuck. I have no issue with turning new parts
 
If you can, make the fixture with a round section on the end that can run in a steady rest. Or adapt a cat head to the end that can run in the steady and set it up as you would turning a barrel between centers. I've seen pics of jigs for truing the face end of an action that are made out of a big tube with two sets of four centering screws. One end goes in the chuck and the other on the steady, the tube is adjusted to run tru and then the action adjusted tru inside with a bar. When you get that far out of the chuck unsupported, there is going to be some deflection even if the bearings are tight and the fixture is pretty rigid. At least there is on the machines I've used.
 
A four jaw independent chuck is the best piece of equipment that can be mounted to a lathe. It is like a cheap rifle scope, on a BR rifle. Get a better 4 jaw than you think you can afford, before you purchase any other toys. Setting up a long bar in a 4 jaw is a process of truing each end in alternating order until the ends are as good as you can get them, or need them. The best tool for bumping the outboard end true, is a copper bar.
I keep a .001" AGD 2 indicator with a mag. base attached to a 1/4"x 1 1/2"x 12" crs plate on the tailstock end of my lathe. Now comes the arguement. I was taught to set the spindle horizontal, on the centerline height. This way the indicator is always ready to contact the workpiece whether it is straight, stepped, or tapered. Once the chuck end is running true, with the jaws snug enough to hold the part, move the indicator to the outboard end and bump the part from the rear toward the front, in line to the chuck jaws. Yes, pull the knob at the rear of the indicator to retract the point while bumping the part. The tiny gears can't take a bump in the nose. Now check the headstock end, and correct the runout. Back and forth...............
One reason for the runout of chucked work is a poor fit between the lower step on the jaws and the tracks which are supposed to hold them down. A lot of old chucks that are not cleaned often will wear at the point of frequent use. As you clamp on the part, the jaw lifts up, causing the top of the jaw to swing away from the part. On this same thought, to those who have milling machines, move the vise to either the right or left on a periodic manner. This wears a wider portion of the table's loadbearing flat surface, and prevents creating a machine that can not make a full X axis travel with the gibs set properly.
Also get in the habit of rolling the spindle a full turn after a part is clamped to prevent a full power crash between a jaw and the ways. 3 jaws are bad for this with large parts. Stay safe, then have fun.
Regards,
Bob
 
My 3 jaw and 4 jaw are both German chucks and pretty tight but for some reason, my 3 jaw had a jaw that just was not the same are the rest. I made 3 jigs from ground plate that I was able to hold flat against the face of the chuck and preload the jaws. I used a dial indicator and played with it until my setup was as reliable as I could make it. I then used a tool post grinder to true the high jaw. It took a LOT longer than I thought. I figured maybe 3 or 4 revolutions and it would be done. it made sparks for a long time. I had it set to just 'touch' the two lower jaws and took a little off the offending one. Whereas I had to clamp a piece of wet-dry in the chuck to make a part even close to centered it is now < .002 at every diameter I have checked. My 4 jaw does a good job of keeping stuff straight- I guess I am lucky! A chuck, especially a scroll chuck, doesn't seem a good place to be frugal.
 
Dennis, you are a man who understands lathe chucks. It is best to use paper shims, or whatever works, amass the wealth needed to buy good chucks. When shopping, look at the features first. Steel bodied chucks are usually stronger, and tend to have a longer life than cast body chucks. Over the years I have found that chucks with the removable top jaws can be used to achieve more goals by using "soft jaws" made of either crs or aluminum. The next $tep up the ladder is a chuck with an adjustable body, that can be used to clamp pieces of like dias. to within .0005"-.001". The same issue with runout on long parts is always there. I have had, and used a 12" Pratt Bernard 4 jaw, and a 10" 3 jaw adjust-tru, for over 15 years with no complaints. If I had to choose between a set of collets, and an adjustable 3 jaw, the chuck would win.
Regards,
Bob
 
Since we're talking about 4 Jaw chucks, I'm in the market to get a top quality 4 Jaw. I have a Yuasa 3 Jaw 'Accuchuck" which still continues to serve me well. My old 4 Jaw has seen better days. One jaw screw was reefed on by a previous owner and as a result will wobble .006" six inches out from the jaws.
Same test bar, the Accuchuck only wobbles .0005".

Update:
Managed to find an 8" Yuasa 4 Jaw new in the box. I've found these Japanese chucks to be exceptional quality fit and finish. I like them better than Bison chucks.
 
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