I am very confused by a video posted on Youtube to adjust a single jaw on a 4 jaw chuck.

J

jbmauser

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I think this is wacky. Am I not understanding?

https://www.youtube.com/watch?v=V7Y3nErVCnc

I don't get it. the error in a single jaw as stated was it was not parallel to the axis of the lathe, not a concentric problem. The correction applied is the method of correcting a three jaw scroll chuck for one jaw being out of true or it is way out of center.

Why would not a grinder run in parallel to the bed against the offending jaw not bring it back into line on a 4 jaw chuck.

This makes no sense to me and if it is correct and I am not I am in big trouble understanding the dynamics and geometry of my lathe. It is possible..... please help a want to be machinist.

JB
 
Wood and bailing wire, not to mention painted pulleys.
 
jbmauser said:
I think this is wacky. Am I not understanding?

https://www.youtube.com/watch?v=V7Y3nErVCnc

I don't get it. the error in a single jaw as stated was it was not parallel to the axis of the lathe, not a concentric problem. The correction applied is the method of correcting a three jaw scroll chuck for one jaw being out of true or it is way out of center.

Why would not a grinder run in parallel to the bed against the offending jaw not bring it back into line on a 4 jaw chuck.

This makes no sense to me and if it is correct and I am not I am in big trouble understanding the dynamics and geometry of my lathe. It is possible..... please help a want to be machinist.

JB
Click to expand...


It seems that the chuck jaws were bell mouthed, and apparently one more so than the others, it is also most likely the he did not have the jaws all the same distance from center when he started grinding.

You are correct, the grinder would grind true to the lathe axis, and the resulting grind on the jaws would have also been true to the axis. Ideally, the jaws should have a very slight taper so that the front of the jaw hits the material first, and then springs a bit as it tightens down for full contact.
 
You are right, if that is an independant 4 jaw chuck, it is wacko, and even more wacko to mark the jaw numbers on the alternate gripping face of the jaws (which are reversible)
Don't understan it at all, although the machine looks immaculate!
Phil
 
Just watched it again, and now I am confused, I suppose if only one jaw was damaged or bellmouthed it might make sense.........................or not?
 
hermetic said:
Just watched it again, and now I am confused, I suppose if only one jaw was damaged or bellmouthed it might make sense.........................or not?
Click to expand...

Well, it did let him do all four jaws in a single operation while minimizing the amount of material removed from any one jaw.

I'd want more loading on the jaws than what his bits of merchant wire could exert, though.

Might as well use wood to clamp a Dremel. The case is kind of rubbery anyway.
 
Just as a complete novice... could you also accomplish this with a boring bar? Is the grinder necessary?
 
Not possible with a boring bar. The jaws are hard. The theory is correct, just not possible with the tool.
 
As far as I am concerned grinding in the lathe & grinding chuck jaws is always a no no, I would rather buy a new chuck, as I am of the opinion that grinding dust & my lathe slides are not compatible, however I have seen it done in an establishment I once worked in, this was to true up a badly bell mouthed three jaw chuck, Even after the guys had carried out their "precision tool repairing" the bother and end results far exceeded the cost of a replacement chuck

The correct thing to do is to take a piece of bright round steel , true up & bore out the middle without altering the setting in other words make a steel ring, place the ring on the outside of the chuck jaws & true it to run accurately on the outside face, This stable ring holds your jaws tightly whilst grinding the inside holding face of the jaws.
 
Another fine example of internet misinformation. He does sound knowledgeable and authoritative. If you work with metal and have a 4 jaw why would you use wood, metal is not strong enough? Bailing wire is not my go to material when I want to solidly stiffen anything. 1/2 hour per pass and 7 passes to get the job done, did he hand feed the Dremel?

I can see some program producer thinking "I have seen a 3 Jaw being trued but never seen a 4 Jaw. Eureka! I have an opportunity for original content"

Caster
 
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