# Chuck Run-out



## ddickey (Sep 6, 2016)

I would like to check the run-out of my three jaw chuck. I will need to get a hold of some drill rod, correct?
I plan of taking my chuck apart for a cleaning first. Any suggestions on procedure will be appreciated.


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## JimDawson (Sep 6, 2016)

I would get a 5/8 x 3 inch dowel pin.  They are straight and round and normally have a mirror finish.  May be available at your local hardware store, if not, McMaster will have them.

Drill rod, unless it's turned, ground, and polished it may not be what you want.


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## mikey (Sep 6, 2016)

You can check run out on a 3-jaw chuck but I'm not sure its worth the trouble since most will have some run out and unless you have an Adjust-tru type chuck you can't do much about it. In addition, anything you turn in the chuck will be on the exact centerline of the spindle unless you take it out of the chuck and then try to re-chuck it.

As for taking the chuck apart to clean it, it would help to post a pic so we can see what the chuck looks like. In general, you will wind out and remove each jaw and then remove the screws on the back rim of the chuck just to one side of the chuck key socket; these are shoulder screws that hold the pinion gears in place. Remove all three and set aside.




Next remove the three screws that hold the front and rear halves of the chuck together. These screws surround the center hole of the chuck.




The back usually comes off easily but if the chuck is old and hasn't been maintained then it may be a bit stuck. Tap the back of the chuck against a wooden block or your work bench and the rear plate will come off.





Then use a hardwood dowel that you can pass into the jaw slots from the front. Tap evenly in each of the slots to knock the scroll loose.




The chuck is now completely apart. Clean all parts and inspect.

Most chuck makers recommend grease for lubricant but most of us users don't do that. We use oil to lube the jaws and jaw slots and grease is used only on the scroll and pinion gears. I use SuperLube oil and grease for these jobs as it does not harden and cake with age.

Okay, assembly is just the reverse of the above. Oil the jaws and the slots they ride in on the front half of the chuck and set aside. I lightly oil the inside of the chuck to prevent rust. Now oil the front of the scroll lightly - you do not need a lot of oil here - and then grease the geared rear of the scroll and insert the scroll into the body of the chuck.

Grease the holes for the nose of each pinion gear that are located on the hub of the chuck body, and then grease each pinion gear. Insert the pinion gears and then replace the rear plate of the chuck. You can re-insert the three body screws and pinion shoulder screws and snug them all; do not overtighten them. At this point  your chuck is mostly reassembled.

The three jaws can now be inserted. Note the teeth on the bottom of each jaw is slightly different, with the number one jaw on the far left having teeth closest to the nose of the jaw and the teeth of the number three jaw on the right will be set back the most. The tooth location of the number two is in the middle of these two.




Now, locate the number 1 slot; it will be numbered. Use your chuck key and advance the scroll until the start of the scroll is just visible, then back the scroll up until the thread is just hidden.





Insert the nose of the number 1 jaw (should also be numbered) into the jaw slot and push it in as far as it will go. Turn the chuck key until the start of the scroll thread is just short of visible in the #2 jaw slot and insert the #2 jaw. Repeat for jaw #3. Note that as you insert each jaw and turn the scroll the inserted jaw will engage the scroll and be drawn in. The reason for the staggered teeth on the jaws is so that when all are in place their tips will be synchronized.

You are now done.

You should perform this maintenance every 3-6 months or if your chuck feels like its sticking due to chips getting caught in the scroll. After you do this a few times it will be a quick job that should not be ignored.

Hope this helps you.

Mike


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## JimDawson (Sep 6, 2016)

Nice write up Mike


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## mksj (Sep 6, 2016)

I would suggest precision ground rod or linear motion rod, I purchased mine from McMasters. You may want to get two sizes, something like 1" x 6" and 1/2" x 12 or vise versa. You can check the TIR at two different clamping sizes, as it can vary. Also check the TIR at various points along the rod to see if the there is an angular skewing from the chuck, and basic headstock alignment.
http://www.mcmaster.com/#precision-shafts/=141o1e5

It is very important to label each jaw/components to the chuck position/slot that it came from, on some chucks they are marked 1,2, 3 etc. Putting them back wrong can make the alignment worse.


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## Charles Spencer (Sep 6, 2016)

mikey said:


> Insert the nose of the number 1 jaw (should also be numbered) into the jaw slot and push it in as far as it will go.





mksj said:


> It is very important to label each jaw/components to the chuck position/slot that it came from, on some chucks they are marked 1,2, 3 etc.




Yes.  I have seen chucks where the jaws had no discernible marks that correspond with the slots on the chuck.  If yours isn't marked then do as mksj says.  If nothing else scratch numbers with your scribe.  I have also seen them marked by center punch dots. 1 dot for the first, 2 for the second...


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## RJSakowski (Sep 6, 2016)

On reinsertion of the jaws, I put #1 jaw in its slot and back the scroll out until the jaw drops down.  Then I advance the scroll slightly to capture the jaw.  Insert #2 jaw to to touch the scroll and advance the scroll to capture the jaw.  Repeat for #3 jaw.

When I scrap internal combustion engines, I save the piston wrist pins.  They are hardened and ground straight and round and make good test pins.  Diameters can range from 1/4" to an inch or more depending upon the engine.

I check for wear with a micrometer.  Generally, there is a position on the pin that doesn't rotate and will not be worn.  I use this for a reference to compare the rest of the pin.  I check diameters at various positions and rotations and discard the pin if there is any measurable difference.  Straightness can be verified by rotating in a V block.


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## ch2co (Sep 6, 2016)

Mikey and the rest
Perfect timing on this explanation. Just yesterday, I started musing on how to go about what you just explained (and very well I might add) how to go about.
Thanks, I'm headed down to the basement right now to do just that.'

CHuck the Grumpy Old Guy


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## mikey (Sep 6, 2016)

Thank you all for the "likes". For many of our newer members, a job like this can be intimidating the first time they tackle it ... well, it was for me anyway. 

DD,Chuck, I did want to add that you need to inspect your parts carefully. Sometimes chips, especially aluminum chips, can weld onto the jaws or slots and you can barely see them. These chucks are precisely machined and there should not be any bumps/defects on the sliding parts. If there are then they're probably chips; pick them off. Also, do not force any of the parts when reassembling the chuck; be patient and get everything lined up and it will go well. 

After you do this job once or twice it will become very simple.


Mike


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## dulltool17 (Sep 6, 2016)

ch2co said:


> Mikey and the rest
> Perfect timing on this explanation. Just yesterday, I started musing on how to go about what you just explained (and very well I might add) how to go about.
> Thanks, I'm headed down to the basement right now to do just that.'
> 
> CHuck the Grumpy Old Guy


Ditto!  I was just thinking it was about time I cleaned up my chuck.  Thanks!


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## ddickey (Sep 8, 2016)

I inspected the inside of my spindle and also indicated it. It has virtually no runout  but look what was inside. Would a Scotch Brite pad work or should I use something else?


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## JimDawson (Sep 8, 2016)

Scotch Brite and some WD40 would be my choice


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## ddickey (Sep 8, 2016)

Upon thinking about this a bit more. Has nothing to do with run out. I guess if you were turning a 1.5" round piece it would. I'll clean it up regardless.


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## mikey (Sep 8, 2016)

Try the grey 000 synthetic steel wool (like Scrothbrite) with WD-40 - will take the rust off without altering the taper.


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## ddickey (Sep 8, 2016)

Okay, rust is takin care of. Here is a pic of my chuck. I have the jaws out. Any ideas how to split it apart proper?


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## Paul in OKC (Sep 8, 2016)

The three outer most bolts are what is holding the backing plate on. The three in the center, and there will be some behind the backing plate when it is removed that hole the two halves together. If you take the cam lock pins out, just be sure to measure how far they stick out currently. When putting them back in put them to them same measure. Not all will tighten up at the same place if you screw them all the way in. As far as the jaws, if not numbered, turn them 'teeth' side up and look at the end that goes in first.  You will notice one with a 'tooth' close to the end, one a bit farther back, one further back still. That is the order they go back in. One closest first, once it catches put in the next, the one furthest back last.  As for checking run out, anything round will work for an initial check. Most 3 jaws will have around .003 minimum, some closer but not the norm. Good luck!


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## ddickey (Sep 8, 2016)

I had the three outer cap screws out. I could not separate the halves. DO I have to take out the cam lock pins also?


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## brino (Sep 8, 2016)

for a good rod/pin for measuring run-out I read here somewhere of using an end mill shank, it just doesn't let you measure very far from the chuck.
-brino


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## fixit (Sep 8, 2016)

ddickey said:


> I would like to check the run-out of my three jaw chuck. I will need to get a hold of some drill rod, correct?
> I plan of taking my chuck apart for a cleaning first. Any suggestions on procedure will be appreciated.


get a wrist pin out of a big block engine. round hard & polished

fixit


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## mikey (Sep 8, 2016)

ddickey said:


> I had the three outer cap screws out. I could not separate the halves. DO I have to take out the cam lock pins also?



You should not need to remove the cam lock pins. The three screws on the rim should hold the pinions in place. The three screws near the center of the central hole are holding the chuck halves together. Remove those screws and the chuck will come apart.


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## RJSakowski (Sep 9, 2016)

You have to be careful on what you choose as a standard for roundness, straightness, or cylindricity.  Hardened drive shafts, for instance have a relatively poor tolerance spec. for straightness, somewhere around .002"/ft.  Drill rod also has a rather poor tolerance for straightness.  

I have run across dowel pins with a bend as well.  A dowel pin is usually used to align two parts that are in close proximity to each other.  Diametric tolerance is important but straightness isn't that important.  I would expect pin gages to be fairly good but I have run into pins that are bent.  They are precision ground for a specific diameter and straightness isn't even specified.

Note that although a tolerance spec. is loose or not specified doesn't mean that a pin, rod, shaft,etc. isn't straight.  There is never an intent to make a crooked part aqnd some are going to turn out well within our needs. Just measure before use.  

Trust but verify!


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## Tozguy (Sep 9, 2016)

ddickey said:


> I had the three outer cap screws out. I could not separate the halves. DO I have to take out the cam lock pins also?



I hope you get some suggestions for separating the back plate and chuck with out damaging the mating surfaces.


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## stupoty (Sep 9, 2016)

ddickey said:


> I had the three outer cap screws out. I could not separate the halves. DO I have to take out the cam lock pins also?



With the screws out you could try ligtly tapping the back plate with a soft face mallet, if that dosn't move it try attaching back to spindle and tapping chuck with soft mallet.  Keep hold of  the chuck to prevent falling damage.

Make sure theirs somthing protecting the ways like a piece of wood as it will just fall off at an inapropriate moment if you don't 

Stuart


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## ddickey (Sep 9, 2016)

Okay I got it all apart, cleaned, lightly oiled and put back together. It wasn't to dirty but I think it was a good idea to clean it up. Thanks for all the help.
I turned a piece of 1 inch aluminum and run-out was .010". I'll check again once I get a precision ground dowel pin.


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## mikey (Sep 9, 2016)

For those readers that follow you, it would help if you told us what you did to get the chuck apart.

Also, if you turned a piece without removing it then you should have near or zero runout unless the piece is really long. Can you post a pic of your set up?


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## ddickey (Sep 9, 2016)

I took the three outer and inner screws out. I had to put the chuck back onto the spindle. Gave it a few blows at an angle with the dead blow hammer and it came apart. Getting the scroll out wasn't bad but I had to use a punch to remove.
I must of made a mistake somewhere as I turned another piece and came out to <.001" run-out.


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## mikey (Sep 9, 2016)

ddickey said:


> I took the three outer and inner screws out. I had to put the chuck back onto the spindle. Gave it a few blows at an angle with the dead blow hammer and it came apart. Getting the scroll out wasn't bad but I had to use a punch to remove.
> I must of made a mistake somewhere as I turned another piece and came out to <.001" run-out.
> 
> 
> ...



Okay, three pinion retention screws and three body screws - thought you had some hybrid chuck or something.

Under a thou for a 3-jaw is pretty acceptable. I bet you could get it under that with a sharp HSS tool.


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## Wreck™Wreck (Sep 9, 2016)

ddickey said:


> I took the three outer and inner screws out. I had to put the chuck back onto the spindle. Gave it a few blows at an angle with the dead blow hammer and it came apart. Getting the scroll out wasn't bad but I had to use a punch to remove.
> I must of made a mistake somewhere as I turned another piece and came out to <.001" run-out.
> 
> 
> ...


If you get .001 runout with a 3 jaw you are a lucky man and the envy of all,


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## ddickey (Sep 9, 2016)

All I did was turn down that 1" aluminum piece you see. Set up my test indicator and it doesn't quit make it to .001". It's .0005" per deviation I'm pretty sure.
I could be doing something wrong cause that does seem very slight for  Chichuck.


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## Wreck™Wreck (Sep 9, 2016)

ddickey said:


> All I did was turn down that 1" aluminum piece you see. Set up my test indicator and it doesn't quit make it to .001". It's .0005" per deviation I'm pretty sure.
> I could be doing something wrong cause that does seem very slight for  Chichuck.


I did not realize that you measured a turned part, these will always be within the spindles accuracy, the thread title is Chuck Runout. Indicating a turned part will tell you nothing about the chuck as it will always rotate the part at the spindle center.

Many people will tell you that you can not trust ground round  parts for hobbyist accuracy, do yourself a favor and buy a 2" long hardened dowel pin say 1/2" diameter and put that in the chuck and indicate it. If you are truly obsessed buy a gauge pin as they do not cost much, one may buy a Go gauge at 1.0001  for a bit over $13.00 from Mcmaster-Carr. http://www.mcmaster.com/#gauge pins


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## ddickey (Sep 9, 2016)

I plan ordering soon.


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## ddickey (Sep 14, 2016)

I got my linear motion shaft today. I got a 1 1/4" x 12" & a 1/2" x 6". I tried the larger diameter at 8" run-out was .015" at 2" it was .010"
I was thinking if I get a chance tonight I'll try rotating the shaft 120° (in the chuck) and see if that changes anything.


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## mikey (Sep 15, 2016)

Have you checked the concentricity of your spindle? I find that information more useful than knowing a 3 jaw chuck is running out by X-amount. The reason is that if you turn a piece in a 3-jaw chuck and do not remove it then it should run very near or at the concentricity of the spindle if the chuck is in serviceable condition. If it does not run accurately then that would suggest you have an issue with the chuck somewhere - jaws worn, scroll worn, etc.

The other thing to consider is that runout of a scroll chuck is typically established at the factory by tightening only one jaw and this jaw is usually marked with a dot, a zero or some other identifier. To find out if the chuck is running within specs you have to lock an accurate test rod in the chuck and tighten it at that designated pinion socket. Otherwise, the specs don't apply. Lots of guys tighten the chuck at all three pinions, which has the potential to throw the accuracy of the chuck out.


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## ddickey (Sep 15, 2016)

I did check the spindle when I had the chuck off. There was very little if any run-out. I think it was .0005". I did notice some spindle movement when I had my test piece in yesterday and lifted up on the piece. Didn't have time yesterday to check other positions. Will be gone this weekend so may have to wait until late Sunday.


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## ddickey (Sep 15, 2016)

I checked the spindle and virtual no run-out. I did however make a mistake on my measurements yesterday. My dial was not in contact the entire revolution so was not getting a true reading. Run-out is ~ .045" I rotated jaws and also changed every cam lock position. The least I could achieve was .037" max was .055". It was not repeatable though when I went back to recheck.
So I have a couple questions.
1. Is it correct that run-out doesn't matter as long as the part is not removed from the chuck?
2. Would new jaws make any difference?
3. Do four jaw chucks have run-out? In other words, can most of the run-out be adjusted out.
4. At this point should I care? I've completed one thing so far (captive nut) and only ever made two other metal projects, (dead center & carriage stop).
My next project will be a machinist clamp.


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## mikey (Sep 15, 2016)

Let me take a shot at this and the others can chime in and correct me.

First, be sure you checked the concentricity of your spindle correctly. That is, run the lathe for 20 minutes or so at moderate speed to warm it up, then shut it off and shift into a gear that allows you to easily turn the spindle by hand. Clean the taper inside the spindle so it is oil and dust/dirt-free and then use a solidly mounted DTI of adequate sensitivity (0.0005 works) and lightly preload the tip with about 0.015" of pressure before zeroing the dial. I usually place the tip at 6 O'clock so I can see the dial easily. Place a mark with a Sharpie on the spindle mount at 12 O'clock and then slowly make one complete revolution, returning the mark to 12 O'clock; the dial should return to zero. If so, then slowly rotate another revolution but look for any deviation from zero and this will be the run out of your spindle. When you do this, make sure you turn the spindle in one direction only. If you are doing this any other way then your results are going to be variable. Concentricity is NOT checked with the spindle running.

To figure out how to clock the chuck, lock an accurate test pin in the chuck and lock it down with the factory-marked pinion (as mentioned above) and check the concentricity of the pin. Normally, I put the tip of the DTI at 12 O'clock, perpendicular to the test pin and very near the chuck jaws. Do the same thing - make one revolution to be sure the dial returns to zero and then another to check how much run out you have and write it down. Now remove the chuck, turn it so the next D1 pin lines up, lock the chuck onto the spindle and re-test the run out as above. One position will give the least amount of run out and that is the position you should always install your chuck in. Most spindles have a witness mark somewhere on the spindle mount; make a corresponding mark on the chuck right across from it so you can install the chuck the same way every time.

As to your questions:
1. If you don't remove the part from the chuck and your chuck is in decent shape (jaws and scroll are okay, no major issues) then the part will have the same runout as your spindle, plus a little more due to cutting loads. It should be at or very near the spindle run out unless your spindle bearings are shot. The amount of "run out" your chuck has with a test bar has little to do with your actual results. Bear in mind that if you take the part out of the chuck and then try to get it back in place then your run out will be greatly magnified.

2. Not unless your current jaws are damaged.

3. 4 jaw scroll chucks do. 4 jaw independent chucks will have as little run out as you have the patience to dial out. It is possible to dial out almost all the run out in a 4 jaw chuck but it can take a few minutes to a few hours, depending on the phase of the moon or the current wind direction. Some days, God just smiles on you ...

4. It is important to assure accuracy when it counts. The trick is to know when that is. In the case of your 3 jaw chuck, I would just accept that it cuts adequately and move on to learning to run the lathe or how to grind a good tool.

Bear in mind that there are adjustable 3 jaw chucks called Adjust-tru chucks and they can be adjusted to run very accurately, enough to satisfy most folks. I don't own one; I use ER collets when I need that kind of accuracy.

As hobby guys we tend to obsess about accuracy and will move the earth to cut something with tenths accuracy BUT there are times when you should do this and times when you don't, and most times you don't. Set a reasonable tolerance expectation and learn to hit it. Otherwise you will spend more time fiddling and less time making stuff and that's what this is all about, right? Making stuff.

Mike


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## Fltenwheeler (Sep 15, 2016)

The new 3 jaw chuck I purchased has maximum acceptable TIR of 0.0016". Older chucks will most likely have more. Even if you have a Set-Tru chuck it will only be right on for the size stock that you used to set it. If I need to turn something true to center I use the 4 jaw chuck.

Tim


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## 4GSR (Sep 15, 2016)

These Chinese 3-jaw chucks are not the greatest chucks out there, but are ok.  I have a Chinese 6" 3-jaw chuck with 2-piece jaws I bought about 14 years ago.  First thing I did was take it apart and thoroughly clean out all of the grinding grit and that strange Chinese grease that was impregnated with grit too.  Borrowed some Texaco grease with moly from work and lightly greased the scroll a gear and re assembled.  With the chuck fitted to the back plate I made, the best runout I could get was .003" at the chuck.  To get it closer, I turned off about .005" off the diameter of the register on the back plate and re-mounted the chuck.  With my  H & G dowel pin I use, I was able to bump around the OD of the chuck and got it within about .00025".  Tighten down the three cap screws and rechecked runout, no change.  Out about 4" from the chuck, runout was about .002".  I can live with that.  For most of the stuff I work on, it is within 1" of the chuck jaws.  I have had to readjust the alignment a couple of times over the years, too, but that is expected, especially at different diameters.  I have to do that on my adjuster-true chucks on my other lathes, too.  Ken


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