How I Refurb Old 3-Jaw Chucks (17 pictures)

[CharlieW]

Hopefully this will help some of you with your chuck issues.

Over the years I have owned several used metal lathes. They all came with 3-Jaw chucks that were well used and not accurate enough to suite me. I used this step by step process to improve them. How much improvement depends on how worn and abused each chuck was.

I recently got a 1947 "Monkey Wards" 10" x 24" Logan lathe. The chuck was pretty beat. This is what I did to it.

The chuck pictured is the original "Logan" chuck that came with the lathe. Notice the grip face of the jaws. They are mutilated beyond usefulness. No chuck should be treated like that.




The first thing is to remove the jaws and degrease all the parts.



The grip face of each jaw, needs to be narrowed to bring it back close to the original width, in order to hold small stock. Excess material is removed from each jaw on the belt sander.

The first thing is to prepare the sander table by setting it perpendicular to the belt.



A guide is clamped to the table to in order to grind the proper angle to each side of each jaw. The guide will need to be reversed in order to grind the other side of each jaw.





Sand/grind the surfaces trying to remove stock equally off each jaw surface.



With care the jaws can be ground fairly accurately on the sander. I only rough them on the sander and finish them on a surface grinder.





The jaws after surface grinding.



The lathe the chuck went on was not operational at the time I did this. Normally, I would perform the next steps on the lathe that uses the chuck. To work around this issue, I mounted a piece of stock in my operational lathe and threaded it to fit the chuck thread.



The chuck has been taken apart. The internal parts, scroll & pinion gear were removed and the chuck halves reassembled. The chuck was them mounted on the threaded arbor.



A tool-post grinder was used to grind the various faces. Grinding the faces is not required in order to refurb the jaws but it squares up the chuck faces and gives it a fresh appearance. I run the lathe in the opposite direction of rotation to that of the grinding wheel though it isn't critical. A slow lathe RPM is used and a very slow feed rate. The grinding takes a long time since only small amounts of stock can be removed on each pass.





Once all the grinding is completed, the chuck is removed from the threaded arbor. It is taken apart and all the parts are cleaned, oiled, reassembled and placed back on the threaded arbor.

A ring is placed around the jaws and tightened holding the ring firmly in place. This takes the back-lash out of the jaws in preparation for grinding the grip face of the jaws. Again a slow RPM and feed is used and several LIGHT passes are made. This trues up the jaw faces, making them concentric to the spindle axis.

The larger 8" chuck holding the threaded arbor went through this process a few years ago when I got the lathe as it was pretty rough and not accurate when I got it.



Remove the finished chuck from the arbor. It is a good idea to take the chuck apart and clean grinding waste off of the parts, relubricate each part and reassemble them. I prefer using oil over grease to lubricate the chuck parts. With use, chips manage to get into the chuck. I find it easier to occasionall remove the jaws and blow the chips out of the chuck. Eventually I find it necessary to disassemble the chuck and clean all the parts with mineral spirits, oil and reassemble the chuck.



Mount the chuck back on your lathe and enjoy a chuck that is as true as it can be made. Notice the narrow grip face on the refurbbed jaws.



Not all chucks will yield great results but this has worked for me quite well on all the used chucks I have had. I have only owned 2 new chucks but I grind the jaws on new chucks to make them as accurate as I can.

I didn't always have a tool post grinder. I have rigged up a Dremel, hand grinder and a home made tool post grinder for doing the grinding. One of the most important things is to dress the grinding stone before using it.
I had a 6" chuck on my last lathe which was 25 years old. It never saw any crashes or embarrassing event that could have damaged it. I kept it clean and oiled and it stayed accurate to 2 thousandths or less runout.

Hope this helps you do yours.

Charlie W.

 

[Old Iron]

Charles
Great info! I bet I threw away 3 chucks that could have been saved. If I would have known how.

Paul

 

[3Spaniels]

Charlie,

Great tutorial! That is one of those posting that will get saved on my computer.

Thanks!
Bill

 

[CharlieW]

The pointy jaws allows you to grind it a few more times without the jaw faces becomming too wide again.

The 8" chuck that can be seen in some of the pictures is the one that probably came with my 1440 when it was new in 1983 and was fairly banged up. It also had the jaw faces ground to where they were too wide. That chuck went through the same process as the little 5" shown. I was going to just buy a new 8" chuck for my current lathe. After reworking it, no need to.

I did this process on my first Logan 200 lathe in 1968. I used a Dremel grinder on it as that was all I had. Funny what you can do as a kid when you have all the time in the world and no money. I was just a teenager then and my dad bought the lathe for me to encourage my interests. It wasn't until years later that I realized what it took for him to be able to buy that lathe for me as I am from a large family.

Charlie W.

 

[GerryR]

Really an informative post. I recently took apart a Bison 3-jaw that I bought new about 3 years ago. the back or the scroll plate had been packed with grease that had dried out. I washed it out in my parts washer, and when re-assembling, only used oil. Is this OK, or should I have repacked it with grease? I figured that a few drops of oil on the pinions would creep into the gears and keep it nicely lubed. Sure does operate much smoother with all that dried grease out of there.

 

[HMF]

Charlie-

Great writeup! Thank you, thank you, thank you for sharing your wealth of knowledge with us. A lot less chucks getting tossed thanks to you.

I urge others of you who have the knowledge to do the same as Charlie and share it, so we can all learn.

Thanks!


Nelson

 

[8ntsane]

Charlie
Nice job, and good write up on the how to.
Only one thing I see thats not quite right. You are using that ring to put load on the jaws, its loading the jaws the wrong way when grinding the chuck jaws. Your jaws should be cranked down the same direction as its used. Your going the opposite direction, unless of coarse your using that chuck for gripping large od rings as shown. If you like , could post a pic of a set up that loads the jaws the same way as in use.

Other wise , nice job done.
Paul

 

[CharlieW]

Paul,
I have heard that comment before. Some people place a plug at the back of the jaws but these small chucks don't have a step like chucks with the reversable jaws do. The other thing is that the scroll tends to be worn more on the compression side than the expansion side. The chuck is suppose to be as accurate when the jaws are being expanded as shown with the ring. I certainly think loading the jaws as they are normally used is fine but I've done 5 chucks like this and I can't see that it makes any difference so I don't worry about it.

Charlie W.

 

[8ntsane]

Hi Charlie
Over the yrs I have rebuilt my fair share of chucks. I dont see any problem with any of your steps, except -1 . You mention your not finding any difference loading the jaws the way your doing it. Now before I get into this, it has nothing to do with chucks that use the bolt on jaws or not.

All of the 3-jaw chucks that have passed through my hands for repair, had the same thing in common. These chucks where used to grip the work inside the jaws. Being this was the norm, all these chuchs showed the jaws belled out at the outer ends. Short work pieces gripped at the ends of the jaws do this over time. Most of use are gripping bar stock on the inside of the jaws, and seldom gripping pieces of tube on the outer side.

The Jaw slots, and jaws allways have some wear. When extending your jaws to grip the ring as your doing, your tipping the jaws outer ends inboard. On every case of chuck jaw regrinding that I have found the jaws belled out at the front. The grinder allways starts to cutting at the rear of the jaws because of this.

Now sleeving/bushing the chuck to tighten a scroll is somthing that is a good thing to do, but a sloppy fit there affects accuracy in a different way. Wear on the scroll is another issue.
Bushing the centre to get it tight again, is great, but the wear on the scroll is somthing that I have not found a way to repair. It is what it is, and somthing that we must live with.

Back to loading the jaws before grinding.Most any of the chucks Ive repaired have bell out jaws enough that one can visually see it. If you take the jaws and blue the gripping surface, and install the bar stock in the jaws, it will show that it grips more to the rear of the jaws, than the front. The smaller variety of chucks this shows up even more so.

I will post a pics of a plate fixture that allows you to load the jaws the way they are used, and you tighten the jaws against this with the same force you would while tightening your work piece. Maybe you have found no difference in the method the jaws are loaded while grinding, but I have. Compressing the jaws as they are used most of the time, and doing this at the end thats belled out, in my eyes makes a difference.

With a fixture such as this, no plugs at the back end of the jaws, and the entire jaws , end to end can be reground as well.









Try it, you might like it

Paul

 

[CharlieW]

Paul,
That is a great fixture. I have not had problem but the chucks I have done all had tight jaws and the ring worked well for me. That being said I see some advantage to the way you loaded the jaws. Nice job and well done.

Charlie W.