6 jaw very weird issue

[UptownSport]

All's Well Then!

Happy New year!

 

[eKretz]

That is not normal or correct, as several here have already pointed out. If the jaws are running out in any way the chuck will be out of balance.

 

[triumph406]

In my field I’m known as a world class craftsman,

 

[Donkey Hotey]

As it turns out, it is correct and normal. For removable/reversible two piece jaws to be able to run true on both the inner surface and and also when reversed, the top jaws have to be different lengths from the inner grabbing surface to the outer grabbing surface. And by kind of a lot. That dimension varies by .025.

My 6 jaw doesn't do that.

 

[EmGo]

My 6 jaw doesn't do that.

I still have no clue what he's babbling on about, since it seems to be beyond world-class abilities to take a simple phone photo and put it in the thread ....

 

[Donkey Hotey]

I still have no clue what he's babbling on about, since it seems to be beyond world-class abilities to take a simple phone photo and put it in the thread ....

Post 13 has videos. It's strobing pretty badly due to the camera and lights but, when it stops, its a normal 6-jaw chuck with reversible jaws. I can't tell if this is a strobing effect from LED lights or it's really running out.

Related: when Haas changed to LED cabinet lighting, they got service calls from customers who said their spindle was stuck. They could hear the motor but, the spindle was not turning. With the door interlocks, they couldn't get to the actual spindle to realize it was strobing of the LED lights freezing the motion at certain RPM.

I'd start by pulling all the removable jaws and comparing their dimensions. Then I'd clamp the jaw carriers around something to firm up the assembly and go around checking the distance to each of the mating dogs.

 

[eKretz]

He's mentioned in text that there's runout on the back side of the jaws when the front side of the jaws are running true. That alone is enough to indicate a problem. I can see the issue just watching the video. There should not be runout on one side when the other is true. Not with one piece jaws and not with two piece jaws. It seems to me that there is either a problem with the top jaws or with the master jaws. His "reversible jaws" are simply two piece jaws where the top jaw unbolts and gets flipped 180°. One piece jaws are generally not reversible, they are usually sold separately as "OD" jaws and "ID" jaws. (Though as pointed out to me by someone here once, not always).

 

[EmGo]

Post 13 has videos.

Whoop-dee-fucking doo. Dropbox does not work with older browsers. They can shove their site up their dripping ass.

Put the damn photo right here where people can see it. If you want to ask a question and have people bother to think and explain, make it halfway easy for them. Like I said, do people in the US have even one quarter of a brain anymore ?

Right here on this very website, when you write a reply, at the top, click "add photo" then drag it to the little box. Really really difficult. It can be an intelligence test, if you're too fucking stupid to do that, you don't deserve an answer.

His "reversible jaws" are simply two piece jaws where the top jaw unbolts and gets flipped 180°.

So how the hell is that supposed to work? Facing one way, the ends are concave. Facing the other they'd still be concave facing the wrong way. Or is he talking about just the pointy part, then holding onto a large bore ? Or does he just mean soft jaws ? wtf is he talking about ? When people get everything wrong, how can you deal with the question ? That's why a simple photo is necessary, because a lot of people don't have a clue what they are doing.

 

[L Vanice]

Measure between the inner face and outer face of each jaw with calipers, see what the range is.

To demonstrate what RN meant, I took the time tonight to perform that test on two Pratt Burnerd and Chinese 6.3" 6-jaw chucks. I bought the PBI new several decades ago and the Chinese chuck is newer, but has never been mounted. The Chinese chuck is a close copy of a Buck and probably had a BTC brand thin round label that fell out of the round recess that just says "IA" (right side of an N and the A). The PBI chuck was quite expensive back then and still is. I found the China chuck on eBay for a relatively low price, but BTC chucks are not very cheap new. Note that PBI chucks have American standard tongue and groove 2-piece jaws, but Buck and the China copies have a Buck design that is only a Buck standard. The difference is important if you are shopping for soft top jaws or replacement hard top jaws.

PBI Setrite chucks, Buck Ajust-Tru and the BTC China Buck copies all fit the same adapter plates with six tapped holes, which can be useful information. Bison and TOS adjustable chucks each need special adapter plates.

First, note that both chucks have the slots, master jaws and top jaws numbered. Both chucks have the short ends of the jaws left as-milled or turned, not ground to use as gripping surfaces, so you could expect some radial runout on those surfaces when any of the precision ground surfaces are in use gripping a centered part. Note that the China chuck has the customary 60 degree included angle at the tall ends of the jaws so that they will close on a small part. But the short ends of the jaws have 120 degree included angles like a 3-jaw chuck. That means the jaws cannot close as far as you would expect when they are adjusted in as far as they can be. Seems like a design error, but I have never removed the top jaws and reversed them to see what happens. PBI used a 60 degree angle at both ends of their jaws.

The Pratt Burnerd (PBI) chuck.


The Chinese chuck.


Now for the measuring results. I used a digital caliper and it is not possible to get precise measurements because the jaw gripping surfaces are ground concave and the caliper jaws are flat. I did the best I could trying to get both caliper jaws located at the center of the chuck jaws' concave shape. Allow more or less .002" for position error.

First, the China chuck, measured from the tall gripping surface to the unfinished outside end of each jaw. The max difference was about .014", which might be visible with the chuck rotating. I would not get upset about it. I did not repeat this measurement on the PBI chuck because I have run that chuck and never noticed any runout on the outside of the jaws.
1. 2.783"
2. 2.773"
3. 2.772"
4. 2.769"
5. 2.772"
6. 2.775"

Now for the measurement that actually counts. First the China chuck, measuring from the finished inner jaw surface to the largest (lowest) finished step. I took a picture of the caliper propped up in the approximate position to take these measurements. Remember, they may be off slightly. The max difference was .003" more or less. Not bad considering the difficulty in measuring.
1. 1.932"
2. 1.935"
3. 1.934"
4. 1.933"
5. 1.932"
6. 1.933"



Now the same measurements on the PBI chuck. The max difference is .005", more or less. I did not go back and take another set. Pretty close to the China chuck and I know from long use that this chuck is very accurate.

1. 1.676"
2. 1.676"
3. 1.678"
4. 1.675"
5. 1.676"
6. 1.673"

So that is the news from Fort Wayne, where lathes and tooling go to rest until the next owner comes along. I have to admit I am not making many chips these days.

Larry

 

[EmGo]

Larry - THANK YOU !!!!

(In other words, a lot of foofaw about nothing. And I don't care for those weird-ass jaws too much, but that's beside the point. All the Bucks I've used had two sets of hard jaws, in and out, or used soft topjaws. Soft is generally my preference).

 

[Donkey Hotey]

He's mentioned in text that there's runout on the back side of the jaws when the front side of the jaws are running true.

Yep. We're all scratching our heads because something that should be easily measurable with a caliper is going on here. After watching an Adam Savage video where his lathe had the change gear knob installed wrong from all the way back to when it was built, I've learned anything could be wrong here. My suspicion is something numbered has the wrong number on it and it's in the wrong spot.

Whoop-dee-fucking doo. Dropbox does not work with older browsers. They can shove their site up their dripping ass.

To demonstrate what RN meant, I took the time tonight to perform that test on two Pratt Burnerd and Chinese 6.3" 6-jaw chucks.

Golf clap for Larry. Well done sir! Why has this not been done by the OP?

 

[eKretz]

Whoop-dee-fucking doo. Dropbox does not work with older browsers. They can shove their site up their dripping ass.

Put the damn photo right here where people can see it. If you want to ask a question and have people bother to think and explain, make it halfway easy for them. Like I said, do people in the US have even one quarter of a brain anymore ?

Right here on this very website, when you write a reply, at the top, click "add photo" then drag it to the little box. Really really difficult. It can be an intelligence test, if you're too fucking stupid to do that, you don't deserve an answer.


So how the hell is that supposed to work? Facing one way, the ends are concave. Facing the other they'd still be concave facing the wrong way. Or is he talking about just the pointy part, then holding onto a large bore ? Or does he just mean soft jaws ? wtf is he talking about ? When people get everything wrong, how can you deal with the question ? That's why a simple photo is necessary, because a lot of people don't have a clue what they are doing.

Most of the more modern hard two piece jaws that I've used have dual radii on the outside jaw steps. They have both concave *and* convex radii. As such:



None of the 6 jaw chucks I've used had anywhere near .015"- .030" runout, anywhere.

 

[EmGo]

Most of the more modern hard two piece jaws that I've used have dual radii on the outside jaw steps.

Thanks, however I would not call those "modern". I'd call them "shitty".

Generally, the point of a 6 jaw is to hold parts as delicately as possible and keep them as round as possible. Therefore, soft jaws bored to the size of the part is what you want to do.

Otherwise, just use a 3 jaw.

None of the 6 jaw chucks I've used had anywhere near .015"- .030" runout, anywhere.

Outsides on the female buck jaws are not ground, they don't touch anything, who cares ? Same with the outside edges of the id-holding bucks. I never measured them, because they touch air, and it doesn't matter.

That's why I'm mystified. It's a set-tru, you can adjust the chuck. From the description I can't even tell what the heck he's talking about, can't tell what he's measuring or why and from the way it's going, I'm not sure he can tie his own shoes so I'm not going to jump to conclusions about the chuck.

And e ? Yours does run out thirty. Let's pop it on the backing plate and I'll show you

 

[Donkey Hotey]

The more I ponder this, the more I'm with @eKretz: the jaws have to be measurably out of spec. The clamped and indicated round surface becomes a measurable datum. If it's within 0.0003" as posted, then any run-out at the back of the jaws is variation in length.

@Lipshurt, you haven't mentioned the origin of this chuck, new or used? You have an indicator. Mount it to the tool post, jog into a feature, zero the indicator and use the carriage dial or DRO to measure deviations.

I'd indicate the outer diameter of the body to run true since that was likely manufactured in the same process as the scroll bore and should all be concentric. Measure everything as a radius from center using the indicator to touch each point (both ID and OD).

 

[Lipshurt]

Just to reiternate:
the chuck has .0003 (3 ten thousandths inches) runout when holding a workpiece the “normal” non reversed way.
when the jaws are reversed the runout is .001. Still very good since the set-tru was adjusted in the normal orientation. This is a cheap 6 jaw from shars. $613 dollars. It seems to be great.
the issue I was asking about is the fact that when it spins, the outer edges are def swinging weird.

the depth of each jaw from middle of concave area of inside to concave area of outside is:
1=2.686
2= 2.673
3= 2.652
4=2.652
5= 2.673
6=2.666

thats a fair amount of variation and you can see it at first glance. I think this is weird. That is why I posted to this forum thinking that someone may have experienced this before. The chuck works great in both orientations of the 2 piece jaws. I still find it weird however. If you feel need to mock my intelligence or abilities as a craftsman, or anything else, go ahead

 

[richard newman]

Thanks Larry for explaining and demonstrating what I thought would be the obvious thing to begin with. Sorry to hear you're not making many chips these days, neither am I.

I also have a P&B Setrite, a 10", bought used in the early 90's. Got it because I thought I'd need it for making hoops for banjos and such, but eventually realized soft pie jaws were a much better solution. As I got older, I got tired of hefting it and got a plain jane 8" Bison with 2 pc jaws. Haven't used the P&B in years. I also noticed the 3 jaw held better than the 6. The guy I bought it from mentioned that also, that was the reason he sold it. I sent it out to P&B to have the jaws reground, didn't make a bit of difference! I guess this last bit would have been more appropriate in the recent 6 jaw thread

 

[David_M]

It seems like you are referring to this piece of the two-part jaws that has the noticeable run-out:

Is this the case?

 

[Lipshurt]

No. That is the “main jaw” and mine do not have visible runout.
the visible runout is on the attached pieces, which are called the “top jaws” or the removable/reversible part

 

[dalmatiangirl61]

Send it back.

 

[David_M]

I agree with dalmatiangirl61 about sending it back.