Clunker lathe chuck rehab method.

I don't know if this has been posted on PM but happened across it just now. I don't agree with the way this fellow loaded the jaws but many of his ideas are/might be worth thinking about. Agree I don't like any using a lathe for A GRINDER. There are many ways to load jaws, but best to load them outwardly. perhaps the simplest is to stack rubber bands to a small C clamp holding each jaw to the Out/Open position so they are tight to holding like holding a part and pushing down on the part.
It seems chuck quality is the bugaboo of many newbee problems and goes on until the newbee finally springs the bigger bucks for a good chuck.

How I Refurb Old 3-Jaw Chucks (17 pictures) | The Hobby-Machinist Forum

michiganbuck said:

It seems chuck quality is the bugaboo of many newbee problems and goes on until the newbee finally springs the bigger bucks for a good chuck.

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A new-arrival does seem to have few choices, yah? We greybeards have scarfed-up any used-but-good ones already, and ain't nobody still making used chucks ennyhow.

Any DECENT scroll-actuated chuck is simply not ever going to be "cheap". ToS Svitav a relative bargain if you "must". Czechs know their stuff.

OTOH, four-jaw have gotten VERY cheap since the Chinese realized that even they could not forever live off the back of garbidge. San Ou shipping quite usable 4-J? It has come to pass.

Mind, I do still have BETTER ones, but at the price? Not worth f**k-with time any longer. Prang one? Just pull the backplate, aside the jaws, scrap the rest. Move on.

20CW

Using the ring to hold the jaws in expansion is incorrect, unless that is how you plan to hold the majority of your work. The jaws should be ground (not grinded) while in compression as in clamping a piece of stock, but even then depending on how much wear is in the scroll or teeth, where you grind it will be only place it is accurate.

Here is a nice drawing of a spider that can be used to hold the chuck jaws in compression while grinding. It does not take much time to make one from aluminum. I used this with a toolpost grinder some years ago and it worked very well.

Chuck Jaw Truing Fixture

ballen above displayed a workable jaw loading device,
The hobby thread appears to be more concerned with appearance.
I will ad two photos showing the wear points inside the chuck, that should be considered for repair before grinding jaws.





Upper photo wear on the pivot for the scroll, can be cut down and sleeved, I happened to use bronze there.

Lower photo shows wear point on the inside thrust face on the front body half, wear here is caused from the pinion wedging the scroll forward. The amount of material removed here will have to be removed from the body half interfaces to maintain correct clearance.

Being lazy, and usually having something else to do other than fix tools, I have just worked a shim in all around the scroll bearing, but obviously a proper sleeve is the proper way to go. The shim works, though.

Also we need to consider that a 4jaw and 3jaw independent may need to be reground, this with loading the jaws (in the right direction) and perhaps indicating the ID (out facing) jaws to be at the same diameter. This for jaw taper and chuck wobble.

ballen said:

Here is a nice drawing of a spider that can be used to hold the chuck jaws in compression while grinding. It does not take much time to make one from aluminum. I used this with a toolpost grinder some years ago and it worked very well.

Chuck Jaw Truing Fixture

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It can help you "somewhat", but there remains the challenge that much of the time a scroll operated chuck has uneven wear and/or "spot" distortion that is position sensitive.

Not much economic gain if this must be done over when changing diameter of the workpiece.

This is not just about THREE jaw scroll, BTW.

It also applies to 2-J, 6-J and 4-J "self centering" OR "combination" scroll operated chucks.

There are two much better ways to go about having a scroll-operated chuck that generates less hassle.

- first is the feature of being able to make minor centering alterations to the whole body. As-in set true, adjust true, tru-adjust - depending on what any given maker calls their version of it. Selecting this type is a VERY wise move on any new purchase. The feature can be, and has been, added to flat-back chucks that were not built for it at the factory, but not always easily.

- the other is two-piece jaws. All of my scroll operated chucks have these: 2-J, 3-J, and 6-J. The "top jaw" may be hardened or soft, and made of steel, aluminium, other metals, even NON metals. "Soft" ones can be readily drilled and bored without need of grinding.

Two-piece top jaws are also a wise upgrade when buying new. Conversions have been done. They are non-trivial work to plan and do, hence not ordinarily worth the effort vs the price of a new chuck.

A less intensive modification is to leave the OEM jaws in-place, drill and tap them so plates can be added. Not easy. Most jaws are hardened.

Not especially strong, either. Note that the "master" jaws of two-piece systems sit low in the body of the chuck so the overall height need not give the advantage of greater prying leverage to the work being gripped. The modification has no such advantage, and will also not have the strength of OEM ridges, dovetails, serrations, or "whatever".

Have a look at the ladner.fr catalog of top jaws for a hint at the "whatever". There are MANY ways two-piece jaws are done by many makers.

20CW

JST said:

Being lazy, and usually having something else to do other than fix tools, I have just worked a shim in all around the scroll bearing, but obviously a proper sleeve is the proper way to go. The shim works, though.

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Being lazier yet, many folks put shims under the jaws. The good news is only when and where it does something useful.

Scroll chucks with imperfections are for the most part just used as they are.

No need for a "spider".

hint- the jaws meet on their sides and are always parallel to each other.

OTOH- a worn chuck will always be a worn chuck

iwananew10K said:

hint- the jaws meet on their sides and are always parallel to each other.

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If that is "scissors" I call "rock".

Even so.. you seen the shite they sell for scissors, these days? "Parallel" and "meet" are not assured!

Well, if you are doing that to fix runout, save your effort, it's not worth it.... all 3 jaw chucks should be assumed to be "out" and the work planned so that is not an issue. If that is not possible or practical, then the 3 jaw is the wrong workholding device.

The only reason I have re-ground a chuck is when the jaws got messed up somehow, or they were bell mouthed. Then it is a reasonable way to save a chuck that has one piece jaws which you cannot find a replacement for.

Likewise, shimming or sleeving a chuck with a worn scroll bearing is another useful way of saving a chuck that you do not want to replace.

Many chucks develop considerable wear also in the guides for the jaws. In my (direct and indirect) experience grinding the jaws when the jaw has already some play in its guide is a waste of time and materials and it doesn't cure the bell-mouthing problem, unless you manage to load the jaws as far out as possible.

One of the first test I would do when assessing a chuck (especially, but not only scroll chucks) is to try to shake each individual jaw in multiple directions at different openings: if it has enough play to feel it, it's likely ready for retirement or to be repurposed to other tasks, like rotary welding tables and similar.

Paolo

Last set of jaws I bought came in over size at the sides and so I had to (surface grind)fit them to my chuck taking some from the jaw sides to make fit with a little slot honing to the tight slot, still have to tickle ID when I find time. glad I did not have to grind the slot sides but would have been easy enough but time consuming on my TC grinder.