My chuck is talking to me, not sure what it's saying

[Harold_V]

>If the chuck has multiple sockets for the wrench, try tightening all of them, as opposed to using just one.
This is SOP - do the same always, including with drill chucks. Never use just one unless I'm drilling cardboard LOL.

That's not a good way to operate when you're seeking the best possible condition. Here's why.

The scroll may or may not be dead centered with the theoretical centerline of the thread. It also may not be a snug fit on the boss on which it operates. As a result, one of the sockets will load the scroll in a better location than the other two sockets. For high precision, that's the socket that should be used (exclusively). If you tighten all three, you lose that advantage. This, of course, assumes the scroll is uniform, not distorted in heat treat, in which case, all bets are off.

Explore which socket offers the lowest amount of runout--then mark that socket. Use it exclusively when precision matters, and always when using soft jaws.

Harold

[stevec]

Tightening all sockets may be SOP for a four jaw but not in my book for a scroll chuck. Try Harold's advice, it's always worked for me.

[Falcon67]

Learn something everyday if you keep your ears open. Thanks!

Having had the chuck apart, I can say that the scroll is real snug on the center bore. Reminded me of the clutch piston in a C4 high gear pack. But I'll just pick one socket and use that, see how it goes.

[JackF]

Good info Harold and I can see why on a scroll lathe chuck. I'm going to check that out on my lathe. I am wondering however if it holds true fore a drill chuck. Years ago I was at a neighbors house , he was a mill wright for San Jose Steel, to use his drill press. We talked as I put the drill bit into the chuck and tightened it, using just one hole. He stopped me and asked why I didn't use all three holes. I of course asked why. He then told me to tighten that bit again as hard as I could using the same hole. He then told me to go to the other two holes and see if the chuck would tighten any further. Sure enough, the scroll "appeared" to tighten more. I have been using this method ever since. I don't use the exact method as the test however; I moderately tighten all three holes then go back and re-do all three a little tighter. In those days, pre machine hobby days, run out didn't mean anything to me, just getting a hole drilled without the drill slipping.

Jack.

[Falcon67]

I'm pretty sure I do the drill chuck like that because my grand dad said to, my dad said to, my jr high shop teacher (the Marine) said do it or drop and give me 20 and my high school shop teacher said do it.

[Harold_V]

I agree 100% in regards to using all three sockets for a drill chuck. It makes a huge difference, and concentricity isn't the same issue it is when you're trying to grip a piece that will end up altered by how it is held. My comments should have been directed solely to a lathe headstock chuck, not drill chucks.

Even a snug fitting scroll will shift to some degree, as the loading is consistently at a given point. Remember, a tenth movement translates to two tenths TIR, so the slightest change in scroll location makes a difference. It may just cause the scroll to lean slightly, but it has always made a difference in operation. It is for that reason that one marks the best possible choice. It's real obvious when using soft jaws. Use any socket but the designated one and you'll see eccentricity.

Harold

[tornitore45]

Furthermore a drill chuck is constructed completely different from a lathe scroll chuck.
A drill chuck has no spiral scroll, the tightening action is the result of the jaws moving axially on a conical surface under a push from a screw ring, therefore all mechanic considerations related to different pinions does not apply.

[stevec]

Furthermore a drill chuck is constructed completely different from a lathe scroll chuck.
A drill chuck has no spiral scroll, the tightening action is the result of the jaws moving axially on a conical surface under a push from a screw ring, therefore all mechanic considerations related to different pinions does not apply.

Mauro, I gotta challenge you on your statement "a drill chuck is constructed completely different from a lathe scroll chuck"
"completely" is my point of contention,
The "scroll" in a drill chuck is an internal thread where as the "scroll" of the lathe chuck is a face thread. otherwise the action performed is identical.
Just my opinion.
Stevec

[tornitore45]

Mauro, I gotta challenge you on your statement

Yes and No, whereas radial movement of the scroll (a spiral thread) have a direct (1:1) impact on 1 jaw and an attenuated (sqrt(3)/2) impact on the other two; radial movement of the "linear screw" (an helix) have no impact and any axial movement is blocked or very effectively resisted under tightening forces.

The fact stays that the cone in mostly responsible for locating the jaws radial position, while the screw determines the axial position.

We are neglecting second order tolerances like a a bit of drunkenness in the screw; a wobbly (tilted) pusher plate or a warped cone surface. All parameter much easier to control than a scroll.

I agree that the two constructions have lots of similarity, observing that a screw is equivalent to scroll on an orthogonal axis carries the duality of construction even further but concentricity really stems from the different functions the scroll and the screw carry out.
The scroll moves the jaws radially, axial movement of the scroll are of no concern but imperfections and any radial movement are.

The screw move the jaws axially on an inclined plane, radial movement of the screw are of no cencern, axial movement are translated into radial jaws movement by the cone, as such the screw control the clamping diameter but can not affect concentricity, only a warped/off-center cone can. By tightening all three holes the possibility that the nose cone is off center is reduced.

I am not in the business of arguing for argument sake, I am more interested in discussing and understanding the mechanic of things, my long response is only to that last notion.

I wander if making the scroll-spigot interface in the form of a ball bearing a tighter fit ergo better accuracy can be obtained. On the other hand if it was so, manufacturer would have already done it and run to the patent office.

[Falcon67]

I finally got it to talk right, after a bit of work. I mounted the chuck, then tweaked it a bit using an indicator on the OD. When I got that close, I put the test bar in the jaws. I had to run the jaws around again to find the best TIR. Once I got that, I tweaked the chuck on the plate using the indicator on the test bar and the tip up next to the jaws. Best I could get was .002 TIR at the jaws, .0035 4" out. At that point I center punched dots on the jaws and chuck in the channels. I went around the chuck and used each scroll screw until I found the one that repeated the TIR. Gave that one a punch mark. Calling it "good 'nuff".

Now for the 4 jaw. The plate doesn't want to pull up to the spindle face evenly in any position, so I'm using a marker to find any tight spots on the taper and massaging the taper slowly with 320 grit/WD-40. I got it to go .003 once, but could not get the cams to repeat at any torque. It looks like a swash plate in all three positions using a breaker bar on the cams. I'll either sneak up on it or have to get another plate. It stands about .003~.004 proud before pull it in with the cams. No matter how may time I go around, there is a spot that won't pull up tight.

[John Evans]

Break out the the marking blue and fit it up. See if there is a obivous issue ie a bump-lump etc. and gp from there. There maybe a tiny piece of swarf imbeded in one of the faces.

[Harold_V]

Break out the the marking blue and fit it up. See if there is a obivous issue ie a bump-lump etc. and gp from there. There maybe a tiny piece of swarf imbeded in one of the faces.

I'd suggest the removal of the pins in order for the plate to be able to be rotated on the spindle. To ensure repeatability, the plate should not fit fully without the use of the cams. The ideal fit is if it hangs when the pins are released, but the plate fits to the flange.

Massaging with fine abrasive isn't going to yield much in the way of results. You most likely will have to remove a thou or more, which will prove to be slow and uneven business with abrasive cloth, so scraping is likely the better choice. Alternately, you can mount the piece and machine the required amount. Grinding would be the best possible solution, assuming it would be one of your options.

Harold