How to Grind a 4 Jaw Chuck

[HBilly1022]

My new King 1236ML (Grizzly G4003) came with 3 and 4 jaw chucks. I recently checked the TIR on the 3 jaw and found it was around 0.011" at 18" from the jaw face, using a piece of 0.75" cold roll steel. So I got out the air die grinding setup and ground the 3 jaw. I just spun it at the highest speed and took very light cuts until each of the teeth had been touched. Now the TIR is less than 0.002" at 16" from the jaw face. Far more accurate than my abilities need.

Now I need to use the 4 jaw so I cleaned all the gunk off and mounted it. Check the TIR and it is about 0.010" at 12" from the face. I checked the runout on the face and the outside diameter of the 4 jaw and it is less than 0.001". So now I want to grind the jaws but not sure how to go about it. I know this subject has been discussed before but my search produced nada. I'm thinking I would use the same grinder setup and hit each jaw separately, ie have one jaw slightly more closed than the others and do this until each tooth has been touched by the grinder. Then repeat with the other jaws. Does this make sense or not?

I'm also concerned about turning the 4 jaw at 1500 RPM (the max speed according to the lathe decals) since the chuck is stamped max 1350 RPM. The next fastest speed is 1000 RPM.

What say the experts?

 

[Wreck™Wreck]

Is this a 4 Jaw scroll chuck?

If an independent jaw chuck why would you grind the jaws?

Last week, three stepped soft jaws and one hard jaw for boring holes for bearings in MIC6 Jig plate.

 

[Bob Korves]

For grinding the jaws a slow speed is usually used, under 100 rpm typically. The grinding wheel needs to go much faster, of course, depending on it's diameter and rating.

 

[HBilly1022]

Is this a 4 Jaw scroll chuck?

If an independent jaw chuck why would you grind the jaws?

Sorry, should have stated it is independent. I want to grind it because the jaws are not parallel to the ways.

For grinding the jaws a slow speed is usually used, under 100 rpm typically. The grinding wheel needs to go much faster, of course, depending on it's diameter and rating.

Thanks BOB. I'm using a air die grinder and it spins very fast. Would you do each jaw individually as I described or use another method?

 

[Bob Korves]

Before you think about grinding more jaws, look at this video for some understanding of chuck jaws.

Also, before you commit to grinding it, test it several more times with a different diameter test bar, and in different orientations, to make sure that you have a true, repeatable problem with the jaws.

 

[chips&more]

Grinding/truing one jaw at a time sounds OK to me. Just make sure it really needs it. And that when grinding, the jaw has the proper load on it. Also, like said, don’t need any high spindle speed for grinding…Dave

 

[12bolts]

How are you going to preload the jaws for grinding? If you place a ring around the outside and tighten up against that for grinding the inside of the jaws, can you be sure that when the load is reversed the jaws wont "cock" over, to be no longer parallel again? What happens if you reverse the jaws? They will most likely no longer be parallel either.
I would just check them for being square to their tee slot. If that is 90* then live with that. Too many variables with using a 4 jaw to grind them parallel in 1 position when you have the possibilities of using each jaw in 4 different orientations. You can shim your jaws at the grip surface if you think one is pushing your work TIR off at one end as opposed to the other. But mostly you should be able to adjust your TIR just by bumping and adjusting the jaws.

Cheers Phil

 

[HBilly1022]

As suggested, I checked it again using a short piece of square stock, about the length I want to use in the chuck, and over that short distance it seems fine. I don't have a longer piece of anything I can trust to be absolutely straight, so for now I will not be grinding the 4 jaw.

The reason this came up is because of a recent project where I used the 4 jaw on my smaller lathe to drill into the end of a rectangular piece of steel before boring. After chucking it up again I noticed the it wasn't true and after a little investigation I found that 2 of the opposing jaws were not parallel to the ways. The other 2 were bang on. As a result, the hole I made did not end up being on dead center. I would prefer not to make that mistake again. Another lesson learned.

 

[RJSakowski]

How are you going to preload the jaws for grinding? If you place a ring around the outside and tighten up against that for grinding the inside of the jaws, can you be sure that when the load is reversed the jaws wont "cock" over, to be no longer parallel again? What happens if you reverse the jaws? They will most likely no longer be parallel either.
I would just check them for being square to their tee slot. If that is 90* then live with that. Too many variables with using a 4 jaw to grind them parallel in 1 position when you have the possibilities of using each jaw in 4 different orientations. You can shim your jaws at the grip surface if you think one is pushing your work TIR off at one end as opposed to the other. But mostly you should be able to adjust your TIR just by bumping and adjusting the jaws.

Cheers Phil

Phil, here's how I did it. http://www.hobby-machinist.com/threads/grinding-my-jaws.50747/#post-426372

It was for a four jaw chuck but it would work on a three jaw chuck as well.

However, if you reverse the jaws, you are correct. all bets are off.