Chuck Run-out

ddickey

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Apr 21, 2016
Messages
3,566
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.
 
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.
 
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.

pinion screws.jpg

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.

body screws.jpg

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.

back plate.jpg back plate off.jpg

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.

disassembled.jpg

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.

jaws.jpg

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.

scroll start1.jpg scroll start 2.jpg

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
 
Last edited:
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.
 
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.

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...
 
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.
 
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
 
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
 
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!
 
Back
Top