Grinding the jaws on my three jaw chuck

[mattinker]

My take on regrinding the jaws on my very old (probably 75 year old!) three jaw chuck. The end is a bit strange, I've cut it short to end better it's not perfect but, better!

Cheers, Matthew

[awemawson]

Nicely illustrated Matthew 

My only addition to your process would be to have used a stone whose entire length can traverse the whole working face of the chuck jaw. This ensures that wear on the stone during the operation has no effect on the diameter being ground as the 'fattest' bit of the stone touches all parts.

Inevitably the stone will wear a bit,  mainly on the leading edge, and even if you dress the stone frequently the inner bits of the jaws will be ground less than the outer bits if you see what I mean 

[mattinker]

Andrew,

point taken, though, these jaws are 75mm long finding a suitable stone would be a bit tough!

Matthew

[awemawson]

Matthew,

The small internal stones I use in my J&S 1300 EUIR cylindrical grinder are supplied as cylinders with a central hole, and can be mounted on an arbor as long or short as you wish.

For a 3" long chuck jaw you need a stone that is relatively short  say 1/2" or so so to meet my criteria would be mounted on an arbor with marginally more than 3 1/2" protrusion from the collet.

White aloxite 46 grade probably be my first choice

[hermetic]

Hi Matt, on the flange where the chuck fits, is there any indexing marks, or odd bolt spacing or alignment pins,  in order to get the chuck on to the flange in the same orientation every time?

[mattinker]

Matthew,

The small internal stones I use in my J&S 1300 EUIR cylindrical grinder are supplied as cylinders with a central hole, and can be mounted on an arbor as long or short as you wish.

For a 3" long chuck jaw you need a stone that is relatively short  say 1/2" or so so to meet my criteria would be mounted on an arbor with marginally more than 3 1/2" protrusion from the collet.

White aloxite 46 grade probably be my first choice

Thank you Andrew, it's done now! I can't see me having another chuck to grind! I'll certainly keep it in mind!

[mattinker]

Hi Matt, on the flange where the chuck fits, is there any indexing marks, or odd bolt spacing or alignment pins,  in order to get the chuck on to the flange in the same orientation every time?

Hermetic,

I have marks on the flange and the chuck.

Matthew

[krv3000]

a job well dun

[mattinker]

Thanks Kev!

[vtsteam]

Glad that worked out for you Matt. 

Since this is a How To and others may be learning, I just wanted to point out a few additional things I think about when I do this operation.

I want to take as absolutely little off of the jaws as I can, because it increases the minimum diameter you can grip with the chuck. I'm mainly interested in removing a small amount of run out by this operation, Nothing more.

It can't correct for an unevenly worn scroll, except for workpieces of the same diameter that the jaws were ground at. Different diameters will again show run out on a worn chuck.

I've had good luck using centrifugal force to keep the jaws out against the scroll, rather than gripping a set of spacers or rings. I just run the chuck at a reasonable speed and it seems to work, for me. Jaws have mass and they do want to move outward on the chuck

My process: I take VERY little meat off at a time, I just feed the stone outward a tiny amount until I just see a few sparks -- not a shower. I make passes completely through the jaw bore and I wait until all sparks stop, and then I stop the lathe and look at the jaws to see which ones are hitting. If all three hit over a reasonable length, I'm done. If not I'll take a tiny additional amount off. Generally the last pass my produce only an occasional spark, until they stop altogether.

I don't try to get a perfect clean face. This takes the minimum off needed to achieve the least run out possible with this method. Just personal preference -- and I don't have really rough chucks to deal with.

[Auskart]

Grinding the Jaws will not help if the Scroll is to badly worn.

[mattinker]

Grinding the Jaws will not help if the Scroll is to badly worn.

Thank you, but I don't think any body said anything different! No miracles, just some improvement!

[vtsteam]

I agree with Matt -- and "badly worn scroll" is one of those blanket statements that doesn't really explain much in a how-to

A chuck with a worn scroll certainly can be improved if the jaws are also unevenly worn or scarred. Grinding will remove one part of the centering error. Improvement doesn't necessarily mean perfection. It just means better.

Also grinding will improve centering if the scroll is relatively evenly worn. In that case centering across all diameters will be better than it was.

Also grinding will improve it if the scroll is worn over the diameters of primary interest in repetitive use in a similar sized gripping range.

If 90% of what a chuck is used for is say 1" diameter stock, grinding at that diameter can eliminate run out at that diameter, even though the scroll is worn, and will not center as well at other diameters. At least 90% of the work will center well, rather than all work needing variable adjustment.

Grinding can't work miracles with a worn scroll, but it may improve matters, depending on where the wear is, what the various causes of the grip eccentricity is, what the use is, and other factors.
 

[awemawson]

Most styles of three jaw chuck can be converted to a 'Grip-Tru' type with a bit of ingenuity to allow precis centring.  The chuck is made a deliberate sloppy fit on the register and four grub screws are placed to be able to move the chuck relative to the register using tolerance introduced by enlarging the mounting holes. When the workpiece is satisfactorily centred the backplate bolts are finally tightened.

Personally I wouldn't want to use this approach on a good chuck, but it's a rescue plan for an older worn one.

[mattinker]

Most styles of three jaw chuck can be converted to a 'Grip-Tru' type with a bit of ingenuity to allow precis centring.  The chuck is made a deliberate sloppy fit on the register and four grub screws are placed to be able to move the chuck relative to the register using tolerance introduced by enlarging the mounting holes. When the workpiece if satisfactorily centred the backplate bolts are finally tightened.

Personally I wouldn't want to use this approach on a good chuck, but it's a rescue plan for an older worn one.

Andrew, that's a useful idea, although in my view, it's a solution if you haven't got a four jaw. If you're going to dial it in with adjuster screws, it's probably easier to use a four jaw.

cheers, matthew

[mm289]

Cheers Matt, very useful. I have a 3 jaw that I was playing with at Christmas to see what the run out was and now know what I could do to it if I ever get around to it !

 

Paul.

[chipenter]

I have a Buck true grip and it's a very good for repeatadly gripping the same size once adjusted for repeat work .

[mattinker]

I have a Buck true grip and it's a very good for repeatadly gripping the same size once adjusted for repeat work .

Good point, I tend to use a three jaw in a four jaw for that!

[awemawson]

So you DO convert your three jaw to a Grip-Tru, it's just that your modification is large and temporary 

[mattinker]

Exactly!!

[AdeV]

Just out of interest, how are the scrolls in a 3-jaw (or any self-centring chuck) made? Rough cast then machined on a mill? Milled from billet? Forged?

I'm wondering.... how hard can it be  to just make a new scroll? This is not a serious project BTW, I'm just curious.

[timby]

We had a scroll made for a special application a few years ago,  it was turned on  a lathe.

[philf]

Just out of interest, how are the scrolls in a 3-jaw (or any self-centring chuck) made? Rough cast then machined on a mill? Milled from billet? Forged?

I'm wondering.... how hard can it be  to just make a new scroll? This is not a serious project BTW, I'm just curious.

Ade,

I would have thought a "useable" scroll could easily be made on a cnc mill.

Make out of heat treatable steel. Rough it out, harden and temper and then finish with a decent carbide end mill.

Phil.

(Do you still want the vice?)

[AdeV]

Ade,

I would have thought a "useable" scroll could easily be made on a cnc mill.

Make out of heat treatable steel. Rough it out, harden and temper and then finish with a decent carbide end mill.

Phil.

(Do you still want the vice?)

Hi Phil,

I did wonder that, but I figured it might be a bit "lumpy"; I may have a go at that one day, maybe make it out of wax...

Vice - Mm, yes please. I only got my car back the week before Christmas, so honest I've not been deliberately avoiding coming over... I'll send you a PM.

Cheers!
Ade.

[WeldingRod]

If you have power feed on the cross slide, you can cut a scroll.  The trick is figuring out what pitch you are going to get!
I cut a scroll thread into my lapping plate many years ago.

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