grinding a three jaw chuck

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BadDog
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Re: grinding a three jaw chuck

Post by BadDog » Mon Apr 16, 2018 11:06 am

earlgo wrote:
Mon Apr 16, 2018 8:18 am
Sorry but I am having a problem visualizing your hex nut spider, unless it is to be gripped inside the jaws. In that case how would one grind the jaw faces.
Set the spider as deeply in the jaws as you can. With the screws near the front of the nut, and the whole resulting spider located at the very back of the jaws, you can access most of the jaw for grinding. Then, if required, clearance the area where the spider supported. But for soft jaws that ledge often forms a valuable back stop for a part.

But if focused on maximizing the effectiveness of improving a bell mouth condition, that would be less than ideal. So coming up with some sort of outboard support would be needed.
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John Hasler
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Re: grinding a three jaw chuck

Post by John Hasler » Mon Apr 16, 2018 11:30 am

Rear support may also cock the fronts of the jaws inward slightly.

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BadDog
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Re: grinding a three jaw chuck

Post by BadDog » Mon Apr 16, 2018 1:05 pm

Even if the support is at the very back of the jaw, I would think it would be hard to get behind the scroll far enough that the force (vector) would tip back to make the jaw tip forward (clamp surface inward). I've used just such a nut-spider to load the master jaws for soft jaw boring, and from my recollection, it's going to be very hard to even get it in line with the force applied by the scroll, much less far enough back to cause it to tip in. Maybe I'm not considering it correctly or completely, but that's my recollection.
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Rich_Carlstedt
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Re: grinding a three jaw chuck

Post by Rich_Carlstedt » Mon Apr 16, 2018 10:11 pm

You need to load the front of the jaws.
Any compression at the rear of the jaws can result in bell mouthing .
Drilling the jaws with a ordinary masonary carbide drill ( 1/8") is simple, just keep it cool so the silver solder doesn't melt.
The hole will be slightly oversize and a 1/8 dowel will slide in.
See this earlier post

viewtopic.php?f=42&t=84427&hilit=grinding+chuck+jaws

Rich

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Re: grinding a three jaw chuck

Post by Harold_V » Tue Apr 17, 2018 1:01 am

What Rich said. If I was to attempt to correct hardened jaws, I'd be inclined to drill a hole in the end of each, then use pins along with a ring. That's the ultimate way to load the jaws, ensuring that they grip on the ends. Even if the are slightly over corrected, the ends will make contact before the rearward portion, ensuring good engagement.

The same consideration for locating the pin should apply if you choose that route. Make sure the pin is centrally located on the jaw face. If it's off center, the forces used to tighten the chuck will cause the jaw to lean to a side, resulting in jaws that still don't run true. That's true with soft jaws, too. Chucks that are in need of this reconditioning generally have sloppy slides, which allow the jaws to move sideways.

I can't think of anything that annoys me more when using a three jaw than to have the jaws gripping only at the inward end. Chatter is almost assured, and the part won't stay where you put it unless you take scratch cuts.

H
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Re: grinding a three jaw chuck

Post by earlgo » Tue Apr 17, 2018 9:06 am

Thanks for the explanation of the spider. I think that in my case, the ring being gripped by the last tooth on the jaws, gave a good result. The line of action was at the plane of the scroll so there should have been no tipping and the jaws were cleaned up front to rear in one setup.
The ring was round with an eccentric hole because of the location of the jaw teeth. Theoretically now the irregularities in the scroll will be the thing to throw concentricity to the four winds.
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Re: grinding a three jaw chuck

Post by ctwo » Tue Apr 17, 2018 9:48 am

search google images for lathe chuck grinding or similar to see a host of neat jaw holding ideas...

I stumbled across a post at PM where the guy did the same as me - by using pieces of angle iron squeezed between the jaws (I think that is about the worst way, but it seemed to work for me).
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Re: grinding a three jaw chuck

Post by Harold_V » Tue Apr 17, 2018 3:58 pm

ctwo wrote:
Tue Apr 17, 2018 9:48 am
search google images for lathe chuck grinding or similar to see a host of neat jaw holding ideas...

I stumbled across a post at PM where the guy did the same as me - by using pieces of angle iron squeezed between the jaws (I think that is about the worst way, but it seemed to work for me).
A rather poor compromise on an acceptable procedure.

Reason?
While the jaws may be restrained, they are restrained from side forces, and may not be spread to conform to the modified condition of the slides, which are sure to be damaged as compared to their original form. For a badly sprung chuck, that most likely would not be acceptable, as the jaws must deflect to the side in order to load the scroll. That would exacerbate the problem caused by using an off center spider. The performance of the chuck may or may not be improved, depending on the nature of the original problem. I'd advise against any type of restraint that does not duplicate the forces generated in the actual use of the chuck, which, more or less, guarantees the desired end result.

H
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Re: grinding a three jaw chuck

Post by ctwo » Tue Apr 17, 2018 11:05 pm

It is not a poor compromise to seek additional information, which is all I posted. I said it was probably the worst way anyway, but I am sure it isn't. It worked more than once...at least to some magical degree that nobody can substantiate, like everything else.

I think the 4-hole plate is best, but would like to try to understand some factors mentioned, such as "the jaws must deflect to the side in order to load the scroll". They need to do that anyway.

I am looking at the forces as point vectors where they are applied. The forces seem to combine to radial forces only. I see the jaws could be out of concentricity though.

Maybe just spin the chuck at 100k RPM and not worry about fixing the jaws.
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Re: grinding a three jaw chuck

Post by Harold_V » Wed Apr 18, 2018 4:24 am

ctwo wrote:
Tue Apr 17, 2018 11:05 pm
It is not a poor compromise to seek additional information, which is all I posted. I said it was probably the worst way anyway, but I am sure it isn't. It worked more than once...at least to some magical degree that nobody can substantiate, like everything else.

Do not take my remarks personally. There are others who read these posts, some of whom may be seeking the proper way to accomplish a given task. To allow procedures to be discussed without pointing out the negative aspects is not serving them well. If there's a problem with an operation, every reader deserves to be told.

I didn't say it wouldn't work. What I said was that the end result would leave something to be desired. It's like oats. If you want nice, fresh oats, you must pay the price (do it correctly). If, however, you can be satisfied with oats that have been run through the horse once, then, yeah, clamping on the sides via a piece of angle iron restrains the jaws. It just doesn't load them correctly. That was my point.
but would like to try to understand some factors mentioned, such as "the jaws must deflect to the side in order to load the scroll". They need to do that anyway.
Unless you and I are not in agreement on what the side definition is, then you don't understand proper loading. You appear to be disregarding the fact that jaws are not a slide that moves strictly in and out. When you apply any side pressure, the jaw favors one side or the other, which won't be the load they see when the jaws are used as intended. This is very easily proven when machining soft jaws, as it's an error that is made by many, including myself. The end result is always an improvement over preexisting conditions--it's just not as good as it can be (concentricity suffers). Seems to me, if a guy is going to go out of his way to improve a chuck, it should be improved to the best possible condition. The jaws should be loaded radially, with no influence to either side. If that is not the case, the results will be a compromise (unless the jaws have **0** clearance, which I would expect to not be the case).

H
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Re: grinding a three jaw chuck

Post by curtis cutter » Wed Apr 18, 2018 9:25 am

I am indeed learning for every post. I am moving toward the conclusion that there are numerous points of wear and or damage that can occur to a chuck but only one symptom can be treated by grinding the jaws.

In the near future I am going to place a narrow object in the center of the jaws.
I will then finger tighten the scroll.
Next place a hose clamp around the outer portion of the jaws furthest from the spindle.
I will place an indicator on the outermost part of the jaws and remove the clamp.
Next tighten the scroll and watch the indicator.

If I see a marked difference in my indicator readings showing outward movement of the jaw, I have wear within the slide portions of the jaw and chuck I will conclude grinding will be of little consequence to this failure.

If I have excessive movement, it will also confirm that I do indeed have a good chuck for a guy of my caliber to learn with and potentially damage further though... :)

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Re: grinding a three jaw chuck

Post by ctwo » Wed Apr 18, 2018 1:30 pm

Harold_V wrote:
Wed Apr 18, 2018 4:24 am
ctwo wrote:
Tue Apr 17, 2018 11:05 pm
It is not a poor compromise to seek additional information, which is all I posted. I said it was probably the worst way anyway, but I am sure it isn't. It worked more than once...at least to some magical degree that nobody can substantiate, like everything else.

Do not take my remarks personally. There are others who read these posts, some of whom may be seeking the proper way to accomplish a given task. To allow procedures to be discussed without pointing out the negative aspects is not serving them well. If there's a problem with an operation, every reader deserves to be told.

I didn't say it wouldn't work. What I said was that the end result would leave something to be desired. It's like oats. If you want nice, fresh oats, you must pay the price (do it correctly). If, however, you can be satisfied with oats that have been run through the horse once, then, yeah, clamping on the sides via a piece of angle iron restrains the jaws. It just doesn't load them correctly. That was my point.
but would like to try to understand some factors mentioned, such as "the jaws must deflect to the side in order to load the scroll". They need to do that anyway.
Unless you and I are not in agreement on what the side definition is, then you don't understand proper loading. You appear to be disregarding the fact that jaws are not a slide that moves strictly in and out. When you apply any side pressure, the jaw favors one side or the other, which won't be the load they see when the jaws are used as intended. This is very easily proven when machining soft jaws, as it's an error that is made by many, including myself. The end result is always an improvement over preexisting conditions--it's just not as good as it can be (concentricity suffers). Seems to me, if a guy is going to go out of his way to improve a chuck, it should be improved to the best possible condition. The jaws should be loaded radially, with no influence to either side. If that is not the case, the results will be a compromise (unless the jaws have **0** clearance, which I would expect to not be the case).

H
We know what you are not so subtly trying to say. It's not even hogwash, but that is OK. You are drawing an absolute conclusion from an unfavorable procedure (or setup). The result could very well be perfection, as unlikely as that may be. Now, I see two opposing vectors in this setup, each working on opposite sides of the jaws, and would very nearly balance, and result in a single radial force. I imagine this allows the jaws to settle where they may rather than holding them in some other orientation.

Which I imagine the 4-hole disc would more likely do, so perhaps that is not as good. Certainly that device applies a similar force to the sides of the jaws, like so many other commercial solutions. I recall seeing a Haas company video where they used a jig similar to this: https://i.ytimg.com/vi/Zlt1-3-6hso/maxresdefault.jpg Notice this jig also only contacts the side (angled) surfaces, but it's interesting feature is in its floating design. I'd have to understand your thoughts on these before introducing the next idea.

I also like the ring and pins into the jaws, and if that method is available then I think it would be ideal.

Seems the scroll is going to push the jaw to one side, too.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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