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

[george wilson]

Do you have any pictures?

 

[joesmith]

Thanks for a very informative thread. I have a slightly different problem with 2 8" d1 4 4 jaw chucks. The first issue is that on each chuck a couple of the jaws are not tight in the grooves of the chuck. Is there a simple fix? Do I need to be concerned?

The second issue with the chucks is face of the chuck has runout on the face as well as on the the steps of the jaws. The d1 mount is integeral to the body of the chuck. These are chinese chucks that came on 13x40 lathes. what is the best approach to improve the accuracy? My concern is what is causing these Inaccuacies--The d1 mount end or the face of the chuck? What is the best way to isolate the problem. I am afraid that just grinding the chuck true might accomplish very little. When I true a piece of round stock with a dial indicator 1/2" from the chuck I still have runout 2" from the chuck.
I know that grinding the inside of the jaws with my toolpost grinder will help this but I may be fixing a symtom--not the real problem.

Joe

 

[CharlieW]

snip... the jaws are not tight in the grooves of the chuck. Is there a simple fix? Do I need to be concerned?

I don't know of a simple fix for loose jaws. It may or may not be a problem. I think it depends on how loose they are but more on whether they hold your part to be machined tightly in the intended way.

The second issue with the chucks is face of the chuck has runout on the face as well as on the the steps of the jaws. ...snip... what is the best approach to improve the accuracy? My concern is what is causing these Inaccuacies--The d1 mount end or the face of the chuck? What is the best way to isolate the problem. I am afraid that just grinding the chuck true might accomplish very little. When I true a piece of round stock with a dial indicator 1/2" from the chuck I still have runout 2" from the chuck.

Determining the problem is always important. I would remove the chuck and run an indicator on the taper and face of the D1-4 mount to determine if it is running true. If it is off, you may have a bent or damaged spindle. If so, what to do about that will require some careful thought.

If the D1-4 spindle mount checks out, mount the chuck and remove the jaws. You can mount an indicator on the cross-slide and indicate the jaw slides. If they do not check out and the face of the chuck has runout, the problem seems like it is with the mount on the back of the chuck.

It is difficult to anticipate all the various posibilities but this would be a good start.

I know that grinding the inside of the jaws with my toolpost grinder will help this but I may be fixing a symtom--not the real problem.

Joe

I think that is a correct assesment.

Charlie

 

[Farmer Dodds]

I have had a problem trying to get some stuff centered in the chuck of my lathe. I had a rusty shaft that I wanted to true up so I chucked it and turned one end to clean metal.
When I turned it and chucked the true end, I could see a slight wobble in the shaft. When I put the dial indicator on it, there was a run out of about 11 thou. on the clean shaft.
I am going to try and mount a hand held grinder on the cross slide to try and true up the jaws.
I have taken everything apart and cleaned it up but could not find anything that may cause my problem.

Great video about grinding jaws. I am going to try it when I get a chance.

Stan

 

[Canuck75]

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

Most interested in seeing your "plate fixture" but photos are not available. Any way to post them again.

Canuck75

 

[littlejack]

I would really like to see photos of Pauls (8ntsane) fixture as well. If at all possible, I would be very greatful.
I have the (belled mouth) problem.
Regards
Jack

 

[Farmer Dodds]

I finally got busy and trued up the chuck on my lathe.
I first made a mount to hold my die grinder on the lathe.

I secured the chuck and started the grinding. #2 jaw was the first to touch.
After 14 thou. the other two started to touch in the back. I don't know how much my stone was wearing.

I was moving in at 1 to 2 thou on each pass.
The jaws ended up pretty clean, but the first segment or bar took an extra 4 thou to clean up on two jaws.

The chuck had some sticky spots when chucking something so I decided to take it apart and clean it.
All of the swarf on the ways was in the chuck.

Once the back was off I could see why it was sticking.
Lots of old grease and cuttings.

After a good cleanup I reassembled the chuck with engine assembly grease and oil.

After a good cleaning and reassembly, the chuck was put back on the lathe. I is smooth now.

So I chucked up a piece of shaft and turned it down, then reinserted it in the chuck.
I is out 3 thou. A lot better than the 11 thou it was out before.

This was a real learning experience as I did not know how this chuck came apart.
The keeper pins for the pinion gears was a little tricky but I finally figured it out.

 

[Canuck75]

Gerry
Buy all means ,steal it , copy it. Hell , I did. I first seen this at another machine shop. The guy had a few different sized ones, including the 4-outer hole variety for doing 4 jaw chucks. The disc that was for the 4-jaw, was hanging on the wall. I had asked the guy about it. His response was, what"? you have to true up 4-jaw chucks too. My response was, ok, enough said, I get it.

Copy it, thats why I posted it.

Paul

8ntsane - Paul

I need to refurb my 3 jaw Cushman and had posted a query earlier with regard to the "plate" that you use to load the chuck jaws in the direction of normal use before grinding. I really don't want to loose the opportunity to see this "plate". Could you post some pictures again please. Your previous post just says the photos are not available.


Canuck75

 

[Catcam]

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.

View attachment 144254

View attachment 144255

View attachment 144256

View attachment 144257

Try it, you might like it

Paul

I agree full with Paul's and 8ntsane's comments the ring around the outside of the jaws pushes the backlash the wrong way. in effect any sack in the jaws is magnified with the process.
the jaws need to be ground when loaded in the same way as they are to be used.
a ring around the outside when machining the outside faces and a plug inside the jaws when machining the inside face of the jaws. It can only work this way.
any comments that it works the other way could only imply that the jaw had no wear and was within tolerances or that no measurements were made on the finished chuck.

The jaws wobble and definitely have a bell mouth in time. The top of the jaws would tilt towards the center, when loaded with the ring. on grinding the jaws and removing the ring the jaws will naturally flex back to their normal position which is the belled out position. Then further on loading the jaws , by clamping onto a piece in the jaws the jaws will flex even further out than before grinding.
this is a poor position made worse not better.

 

[benmychree]

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.

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View attachment 144225

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

View attachment 144226

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.

View attachment 144227

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.

View attachment 144228
The only thing I can find fault with is when you internally regrind the jaws, you back the jaws out against a ring; If the scroll is worn, it will not run true when chucking pressure is inward on a round work piece: when this regrind operation is done, the chuck jaws should be stressing inwards, not outwards, that is they should be stressed for grinding in the same direction as the chuck is being used, This is not so easy with solid jaws such as you illustrate, but there are several ways; one that I have used is to drill a hole in the face of each chuck jaw in approximately the same location on each,; this can be done with a carbide drill. Then insert a pin in each hole, projecting about 3/16 - 1/4" and then cut a ring such as a piece of tube or pipe which is sized to allow the internal grinding wheel to enter and chuck down on it with the pins and proceed with grinding. This procedure loads the jaws in the best position for parallelism with the work piece when in use, the chucking a ring as illustrated does just the opposite. On chucks with reversible top jaws it is much easier, we just cut pieces of hex stock ( pieces of a Allen key can be used) to match the Allen bolts that hold the jaws on and chuck down on them as with the pins used with the drilled holes.
View attachment 144229

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

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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.

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The jaws after surface grinding.

View attachment 144233

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.

View attachment 144234

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.

View attachment 144235

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.

View attachment 144236

View attachment 144237

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.

View attachment 144238

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.

View attachment 144239

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.

View attachment 144240

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.