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Dave Hoskins

Dave Hoskins

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5,252
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Parker County, Texas
I have always wondered, and am finally getting around to asking this. On the Nova Chucks, and I am sure others as well, each jaw is numbered as well as the location on the chuck itself. Does it actually matter if you put the #1 jaw in the #3 spot? Is there a balance thing going on which demands the actual numerical placement be exact? Just curious.
 
Inside a 3 jaw chuck there is a threaded plate. On the jaws there is a thread that mates with the start on the threaded plate. Putting #1 into #3, then #2 into #1 then #3 into #2 locations will cause the jaws to close in an odd pattern and not clamp properly.

Now, would is be OK to put #1 into #3, then #2 into #1 then #3 into #2 while making sure the #1 jaw starts first, then #2 jaw starts second and #3 starts third? I don't believe it would make any difference. I have always put #1 into #1 and never violated that, so, I do NOT know for sure. I do know how the chucks work as I have worked with them through my career.

As to balancing, I don't believe chucks are balanced with jaws in place. That would mean you would never be able to swap out jaws with different jaws. I have mounted a hugh variety of jaws on a lot of different chucks. Chucks on wood lathes are no different.
 
I just realized I stated my question wrong. I meant does it matter for sure if you do or do not put the #1 jaw in the #1 spot, and etc. with 2,3,&4. Though I think the answers wil remain the same. I'll just keep putting #1 in the #1 spot on the chuck. One of those things that eventually ya gotta ask.
 
Dave, it's my understanding that the 4 jaws are machined as a unit (separate from the chuck itself), so keeping them in numbered order ensures that things mate up as symmetrically as they were machined. My guess is if you put the #1 jaw in the #2 spot, and the #2 jaw in the #3 spot, etc. and worked your way around the set in numerical order, it'd still run true.
 
Don't know about the Nova chucks, but my barracudas all have a little pin in the #4 jaw that fits in a slot under the #4 jaws... if you shift all the jaws one slot, then the pin will make the jaw sit crooked (or as my grandmother would say "whonkerjawed".... as a point of rule, I always use the numbering system to keep them straight... I have 4 chucks each with a different set of jaws, so rarely have to change them... also have a Grizzly Barracuda style chuck that has a set of #3 jaws that I never change as the PSI jaws won't fit... a disappointment when I bought the chuck.
 
From the manual:

"You will notice that each jaw segment is numbered 1-4 on the bottom or top face. Jaws should be mounted clockwise in the same sequence. This ensures the jaws are re-assembled the same way they were cut during manufacture. This will ensure optimum accuracy."

So my assumption has been that they grind the jaws on a machine in the order defined and you're most likely to have concentric setup if they're kept in that order. Some of the machinist forums tend to agree with that assumption. From what I can tell you're unlikely to have problems rotating the jaws so they don't match the body as long as they're kept in order as I don't think the chuck<->jaw machining has that much variation. In practice keeping the jaws matching the body is convenient to ensure order so.. I usually just do that.
 
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