# HF 9x20 Chuck runout question



## weejax (Aug 11, 2022)

I am getting around .003 of runout measuring about 1inch from chuck jaws.  I used a number of different items (bar stock, drill rod, end mills) and got roughly the same result (some worse, .003 was the best i could get).    I measured spindle bore runout and it is a little less than .0005.  Is that acceptable?  the chuck came w the mill, I have no idea what its provenance is.  I took it apart and cleaned it.  as you can see in the photo the jaws seem to meet nicely in the center.  I did not mark the jaws when i took it apart and spent a while switching them out to get it to pull all of them to center.  So, is .003 to be expected?  Should i try and get new jaws?  Or, get a new chuck?  Thanks for the help!


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## DavidR8 (Aug 11, 2022)

A three-jaw chuck will have runout, maybe in the range of .001 - .003 but it's not typically a worry.

A chuck with excessive runout can still cut concentric parts, so long as the workpiece is not removed from the chuck until all cuts have been made.

Many things can affect runout in a 3 jaw chuck.

Any dirt, chips on the mounting surface of the adaptor plate (if there is one) need to be cleaned off. Any dings may need a quick stoning to remove high spots.

The chuck jaws need to be clean, including the internal scroll mechanism. My chuck is currently a bit sticky and I'm going to pull the back and do a thorough cleaning.

I would remove chuck from adapter and check runnout of the adapter. If there's runout on the adapter then even if the chuck was perfect there would still be runout.


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## rwm (Aug 12, 2022)

...and this is why people use 4 jaw chucks when they really need accuracy.
Drill rod and stock will contribute to the error. You should really use a dowel pin or gauge pin. Keep in mind that the error will also vary with the dimeter you choose since each diameter corresponds to a different location on the internal scroll.
For fun I just checked my expensive Bison 3 jaw. I had 5 thou of TIR. I cleaned the jaws and re-chucked the pin. Then I only had 1 thou. Obviously a chip in the jaw screwing with me. A larger pin shows 2 thou TIR. 3 thou is not a bad runout but test with a more precise pin.
As David said, your parts will still be round and concentric with the lathe axis. If you index the part with a sharpie before you remove it, you can usually get repeatable concentricity.

(Sorry, I initially missed that you said "end mill." That should be fine for a measuring pin)


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## Bi11Hudson (Aug 12, 2022)

Most any *3 jaw chuck can*, and often does, have runout at some point of gripping. Like the others above, 0.003 is not too bad. Not perfect, but not bad. In all of history, there's only been one perfect man, and they've been putting erasers on pencils ever since. Even high end chucks can have runout, for several reasons. A practice you might find useful, if there isn't time to properly run down the real problem, is to determine which sequence of jaws is closest to true center, This is a very real problem, and the older the chuck, the more noticable the misalignment is.

The first time you do this, it sounds complicated. The second time is quite easy, and the third you wonder "why I didn't think of this myself". Remove the jaws, set them in sequence, and mark them 1-3 with a file or grinder. The jaws are usually hardened, a punch mark won't cut it. Number one(1) will be with the teeth closest to the gripping end. Looking into the slots you will find the "scroll" that moves the jaws. Brush any chips out, a tooth brush works well here. It will take several rotations of the scroll to get things reasonably clean. Cleaning the chuck scroll *can* be with the chuck body on the bench. The chuck must be mounted to test runout. Be sure the spindle threads are clean as well.

Rotate the scroll to where it is almost but not quite in a slot. Insert the Nr 1 jaw here, marking it with a sharpie or some other erasable mark. proceeding to Nr 2 and 3 as the scroll is rotated. Chuck up a test bar and record runout. Remove the chuck jaws and start Nr 1 jaw in the Nr 2 slot, repeating the tests. Then with the Nr 1 jaw in the Nr 3 slot, again repeating. This test *could* be repeated several times, depending on how well the test bar is chucked.

With the tests complete, determine where the lowest runout is. Mark that slot with a punch as Nr 1. The chuck body is softer than the jaws so a punch mark will work. Mark slot 2 and 3 as well. Also put a witness mark for the chuck body and the backing plate. That way when the chuck is disassembled for cleaning, which *should* happen regularly, it can be reassembled as it came apart. Follow this with the "outside" jaws, marking the jaws with a sharpie until they are registered. Then with a grinder or file.

This test defines the "lay" of the chuck. I don't know the proper machinist's term for the process. When the chuck is assembled by the manufacturer, this test is usually not a part of the assembly process.  Further, the chuck likely hasn't been properly cleaned, All of this can effect the accuracy of runout. A HF machine, and many others, seldom come from the supplier "ready to run". Some tune up is as important as gaining the "feel" for a particular machine.

My terminology is learned from very old (>100 yo) books, long before the Internet was a "thing". The terms used may be "incorrect" by modern usage. This is the sequence I followed with a Grizzly model made in Taiwan. The recent version is G-4000, made in Mainland China. The brother to your HF machine. I use a Dremel with a cut-off wheel to mark the jaws.

.


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## weejax (Aug 12, 2022)

thanks everyone for taking the time to help!  I learned a lot.  this is a great group


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## DavidR8 (Aug 13, 2022)

weejax said:


> thanks everyone for taking the time to help!  I learned a lot.  this is a great group


Yup, it is a great group!


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