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LFL
04-18-2009, 05:58 PM
My friend, Frank, has a Colchester lathe (Master Mk II 13 X 30”). We bought a Chinese 4-jaw chuck from Wholesale Tools, it is a 10” one. We first tried to use a L0 backing plate we had, but it was out of spec. It wouldn’t sit on the spindle taper correctly, only about 3/8” would contact the spindle and it would not fit on the spindle repeatably.

We bought a new backing plate from Wholesale Tools, it fits well and repeats well. (by repeats, I mean it will go on and off and give the same reading on a DTI.) We cut it to fit the chuck back and trued it to the lathe axis.

We cut the backing plate to fit the chuck and mounted the chuck. I put a polished steel shaft, about 1 1/8” dia and 10” long, that appeared to be straight, and dialed it in close to the 4-jaw. When I checked it 8” out from the chuck, it had .030 runout in it. It was visibly out of true.

We took a chunk of steel bar stock, 2” dia and 6” long, chucked it up in the three-jaw, and made a truing cut on it so it was concentric. We then mounted the 4-jaw on that piece, dialed it in radialy (using the register to indicate from) and got it true. Then we cut the flat where the chuck fits to the backing plate. My thought here was to get the jaws to be true to the lathe axis, by having them on a piece that was known to be true. Then we could cut the chuck back to fit on the backing plate. We know the backing plate runs true, it checks out OK with the DTI. Then the chuck jaws should be true to the axis of the lathe.

However, it did not work out this way. When we reassembled the 4-jaw to its backing plate (being careful to keep it clean and free of debris) and mounted the 4-jaw to the spindle, I ran the same check with the 1 1/8” polished bar and got the same .030 runout.

Just in case the bar was bent, I tried a smaller piece (3/8” dia X 8” long) and got similar results. About .025” runout.

Guys, I am stumped as to what to do next. Any suggestions? My goal is to get the 4-jaw to hold a piece true to the spindle axis, it won’t do it now.

Steve

quadrod
04-18-2009, 06:50 PM
i'll watch this thread with interest, i chucked up a shaft in my four jaw awhile back and dial indicated it in at the chuck. then eight inches out i had lots of run-out, say .050". i spent awhile taping with a mallot and rechecking at chuck and out at the end till i got it trued up. i thought that was normal. for me i would not expect any chuck to be true at the chuck jaws and out any distance from the jaws with out lots of fiddling.

lane
04-18-2009, 07:19 PM
i'll watch this thread with interest, i chucked up a shaft in my four jaw awhile back and dial indicated it in at the chuck. then eight inches out i had lots of run-out, say .050". i spent awhile taping with a mallot and rechecking at chuck and out at the end till i got it trued up. i thought that was normal. for me i would not expect any chuck to be true at the chuck jaws and out any distance from the jaws with out lots of fiddling.

Correct. That is the way to do it . You must indicate both ends of shaft. Tap tail stock end true with hammer are brass bar.

doctor demo
04-18-2009, 09:50 PM
Steve, just curious if You can or have checked the chuck to see if the face runs true on the lathe. It sounds like You have a case of Asain Chuckitis.

Steve

PS Welcome

Steve Steven
04-18-2009, 10:51 PM
No, the chuck face does not run true. I really don't care about that, I just want a bar held in the jaws to be true on the free end when the chuck end is dialed in.

Lane,
How can I get the free end to true up when the jaws will not hold it true? I need the jaws to be parallel with the rotational axis of the lathe, don't I?

Is my next move to just grind the jaws in place so they will be parallel? Thats what I am looking at next.

Steve

PS I started this thread on Franks login, thats why my name is on this one, I am on my computer now.

quadrod
04-18-2009, 11:01 PM
i may be wrong, but even if you grind the jaws you may still have the problem of having to true the free end too. in order for the jaws to move in the T-slots of the chuck there has to be some clearance witch will always show up some distance out from the chuck face and jaws.

J Tiers
04-18-2009, 11:59 PM
If the chuck face does not run true, the chuck is almost certainly not aligned with the axis of the spindle. Unless of course it is a trash chuck, in which case why are we here?

Almost any chuck company will be certain to make the OD and face of their chucks run true when the chuck is correctly aligned. So if the face does NOT run true, you probably need to remount the chuck so it does.

Otherwise, you WILL have the problem of the stock held being "out" at some distance from the chuck. You might anyway, of course, for a variety of possible reasons. But if the chuck is mounted cockeyed, you can only expect the stock to be held "out".

doctor demo
04-19-2009, 12:12 AM
No, the chuck face does not run true. I really don't care about that, I just want a bar held in the jaws to be true on the free end when the chuck end is dialed in.

.
If the chuck face doesn't run true ...when You chuck a shaft and dial it in it will only be dialed in that one spot. It would be the same if the 3 jaw face didn't run true. The jaw alignment is ''in theory'' perpendicular to the face.
Think about it You will get it faster than I can figure out how to explain Myself.

Steve

oldtiffie
04-19-2009, 12:38 AM
Use your 3-jaw chuck to turn a cylinder of say 2" diameter x 3" long.

Mount your 4-jaw chuck - with the jaws facing the head-stock - onto the turned cylinder. Adjust the 4-jaw with a good test dial indicator (TDI) until the 4-jaw chuck outside diameter of the chuck near its "front" is as good as you can get it.

Now put the TDI on the 4-jaw chuck and check for run-out at the front and back faces as well as the outside diameter at the "back" of the 4-jaw chuck.

You will now have a good idea of the run-out of all these surfaces relative to the gripping faces of the jaws as well as each other.

It might be a good time to think about taking a "skim" cut from the back of the chuck where it locates on the spindle flange - but don't touch or remove any metal from the presumably "D" location taper/spigot.

Did you get a set of specifications with your chuck? Here are 2 that came with 3-jawed chucks that I've bought recently:

http://i200.photobucket.com/albums/aa294/oldtiffie/3-jaw_chuck_specs1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/3-jaw_chuck_specs2.jpg

Peter.
04-19-2009, 04:13 AM
No, the chuck face does not run true. I really don't care about that, I just want a bar held in the jaws to be true on the free end when the chuck end is dialed in.

Lane,
How can I get the free end to true up when the jaws will not hold it true? I need the jaws to be parallel with the rotational axis of the lathe, don't I?

Is my next move to just grind the jaws in place so they will be parallel? Thats what I am looking at next.

Steve

PS I started this thread on Franks login, thats why my name is on this one, I am on my computer now.

If you grind the jaws to run true with the body running out you'll always have to make sure they go back in the same holes. Also, if you don't figure-out now why you have your runout you don't know if the runout is going to be repeatable so you might have ground your jaws for no gain.

airsmith282
04-19-2009, 07:07 AM
ok i dont use a four jaw chuck yet my self and god help me when i do , anyhow , my question would be to take in question the tail stock alignment for proper centering , iam your jaws are different style are they not , then whats in the 3 jaw chuck so even shimming it might need to be done heights could be a factor would they not i wounder.. perhaps check the jaws them self for even a small burr of any size at all this would knock it off at the jaw area even if the chuck it self ran true,.. also is your live or dead center free of debre or worn out etc, take some extreamly light light cuts at at a time see what happens.. iam just putting out some ideas here,

Glenn Wegman
04-19-2009, 08:56 AM
Assuming it is a plain back chuck and you have already determined that the error is not in the adapter plate:

Take about a foot long piece of 1.5" dia or so round bar and put a center in each end. Turn it between centers and make a clean up cut on it. Center it up in the 4 jaw and then remove the chuck with the bar still in it from the lathe. Remove the adapter plate from the chuck. Put the assembly back in the lathe between centers. Now you can roate it and see if/where the possible error is in the machining of the chuck itself. If you are not happy with the outcome you could always spin it and take a light clean up on the mounting face of the chuck, By doing this the mounting face will now be perpendicular and true to the axis of the jaws.

May be an option if it is a machining error when the chuck was made.

Glenn

John Stevenson
04-19-2009, 09:17 AM
I had some Indian chucks in a while ago from a well know Northern UK seller what were out.
He wanted to know if they could be trued up.

After a lot of fiddling with one it was determined that the slot for the jaws to sit in had been machined whilst the body was tilted.

Even truing up as explained in the first post only worked on one diameter. Further checks to find out why revealed that as well as the slots being out the jaws were not square either.

Reported back and was told to scrap all 10.

By swapping jaws i got one close and fitted that with bearings and a MT4 shank and used it on my lathe to hold welded shafts good enough to get a diameter turned on them for a steady.
That paid for my time.

One had a piece of 3" angle iron bolted onto the back and that fits in the vise to serve as a vise for odd shaped components.

One was used in the buildup of my welding positioner bearing in mind that the errors on this chuck are far less than my welding skills :D

The rest were given to friends for whatever purpose other than lathe chucks.

Barrington
04-19-2009, 10:45 AM
Use your 3-jaw chuck to turn a cylinder of say 2" diameter x 3" long.

Mount your 4-jaw chuck - with the jaws facing the head-stock - onto the turned cylinder. Adjust the 4-jaw with a good test dial indicator (TDI) until the 4-jaw chuck outside diameter of the chuck near its "front" is as good as you can get it.

Now put the TDI on the 4-jaw chuck and check for run-out at the front and back faces as well as the outside diameter at the "back" of the 4-jaw chuck.

You will now have a good idea of the run-out of all these surfaces relative to the gripping faces of the jaws as well as each other.

It might be a good time to think about taking a "skim" cut from the back of the chuck where it locates on the spindle flange - but don't touch or remove any metal from the presumably "D" location taper/spigot.

As I interpret Steve's first post he's already done a skim (?) which makes me think there might not be a real problem - all the runouts have been observed using polished rods of unknown (and possibly dubious) character...

With a proper test bar it might be much better ...?

Cheers

wierdscience
04-19-2009, 11:03 AM
I think your problem is what John mentioned,jaw slots milled off plane.

Send it back and trade up to a Bison or TOS chuck.

pressurerelief
04-19-2009, 11:15 AM
I will second the vote from Weirdscience on the bison chuck. I have an eight inch six jaw (I do alot of hex work) from Bison and it is as advertised if not better. A chuck is not somewhere to save money in my opinion, watch what you spend yes but skimp, NO.

P/R

Steve Steven
04-19-2009, 11:23 AM
As I interpret Steve's first post he's already done a skim (?) which makes me think there might not be a real problem - all the runouts have been observed using polished rods of unknown (and possibly dubious) character...

With a proper test bar it might be much better ...?

Cheers

Yes, what Oldtiffie said is exactly what I did. To get the face and periphery running true, I will have to put the chuck (without jaws) in a larger 4-jaw chuck, get face and outer rim running true, then recut the register face and see if that will fix it.

Is this what everyone recommends? Will it make the jaws be parallel to the spindle axis? I don't have a chuck big enough to chuck this 10" 4-jaw, I'll have to ask around and see if I can find one somewhere.

Steve

J Tiers
04-19-2009, 11:44 AM
According to Tiffie's specs, which appear to be for some asian chuck, and therefore possibly are NOT actually met by the real part.......

Fors 250mm chuck, the test bar at 2" (50mm) from the end of the jaw should be "out" no more than 4 thou (0.1mm). So at 8", you would expect a maximum of 4x that, or 16 thou, per the Tiffie spec.

You get double that, but we don't know the spec of your chuck.

Since that is from the END OF THE JAW, if you measured at 8" from the chuck FACE, your measurement with a 10" chuck would be expected to be at around 6 inches from the end of the JAW.

In that case, your measurement per the Tiffie spec would have been a max of 12 thou, but you get almost 3x that.

We have NO idea what the relation of your chuck to the Tiffie chuck is.....

However, it sounds like one of the following is the case.....

1) your mounting is still not holding the chuck correctly

2) the chuck is simply not made very well, and that's as good as it gets

3) the chuck is out of spec for some unknown reason.

Barrington
04-19-2009, 12:19 PM
I would say again -

If not using a test bar of known characteristics, then there is no real 'measurement' of the runout at all...

Very few pieces of rod found lying around would be straight enough to use 'as-is'.

Machining the front face of the chuck isn't going to help with runout, but it will give a reference surface to clamp up against for some jobs.

Cheers

J Tiers
04-19-2009, 02:44 PM
Machining the front face of the chuck isn't going to help with runout, but it will give a reference surface to clamp up against for some jobs.



I've no idea what machining the front would be expected to do aside from the surface ref...... it's basically just washing a pig.

But if the front is well "out" the odds are the rest of the chuck is not running true, OR that the whole thing is just "pretty-looking scrap".

franco
04-19-2009, 11:09 PM
Steve,

I bought a new (cheap) 6" 4 jaw chuck from a machinery dealer's closing down sale several years ago. Runout for an item which was indicated true at the chuck jaws was very bad indeed as distance from the chuck increased - more than 1/2" at around 8" from the chuck from memory. I checked everything I could think of - the back and front faces were square with the periphery of the chuck, the backplate was true, and the jaw faces were reasonably square with the jaw threads. I did exactly what Tiffie suggests to check the chuck, i.e. mounting it by tightening the jaws on a bar which had previously been turned true, and indicated the middle of the periphery true. I found there was considerable runout of the chuck body. Out of sheer frustration and without thinking it through I then did as you propose and took a skim off the chuck back to see if there would be any improvement. This was the WRONG thing to do, in this case anyway. It only seemed to make the problem worse everywhere except at the diameter of the bar the chuck was mounted on, and the resulting run out of the chuck body looked b..... awful.

Further checking finally revealed that the chuck jaw slots had been wrongly machined as John S described. Opposite pairs of slots were parallel to each other but not in the same plane, and were not parallel to the chuck face.

Because the dealer had closed by the time I had made a backplate, I was not able to return the chuck, but was able to make it usable after a fashion by re-skimming the back so it was square to the periphery again, then grinding the jaw faces with the chuck in place on the lathe. After this it would hold material reasonably true, because, though not in the same plane, the opposite pairs of chuck jaw guides were parallel to each other, so the newly ground jaw faces were also parallel to each other, though no longer square with the jaw threads, and so could hold the workpiece parallel to the lathe centerline. Of course, it was near impossible to get anything to run true on the jaw steps, since I never tried to grind them true. That chuck has now long been retired to occasional use on a rotary table.

I have no idea if this is your problem, but I would suggest being very sure that there is no more simple explanation before taking a skim off the chuck back. Even if skimming the chuck back out of true does fix the problem, the sight of the chuck body wobbling as it rotates is horrible!

John S.

Were the faulty chucks you got roughly hand stamped "CENTRAL" by any chance? This was the only identification on the chuck, and there was no clue to the country of origin, though I have my suspicions!

franco