# Truing up a chuck.



## GaryK (Feb 1, 2013)

This is not something I really plan in doing so this is merely an exercise.

Suppose you have a chuck with jaws that are slightly out of whack. You get the chuck body running true and a rod TIR is good 1" out from the jaws.  
Then you measure 10" from the jaws and the TIR is way out.

What I'm wondering is if anyone has ever trued up the back of the chuck based off the jaws. Look at the following pictures.





Mount a bar in a chuck or collet. Turn it to true it up perfectly with a live center. Then slide the chuck over the bar and tighten the jaws.
I would thing that this would align the jaws with the bar. Then any difference in square should show up in the back of the vise.

My question would be how do you think this would work to square up chuck by taking a skim pass on the back of the chuck. (of course removing the pins first)
Would it stay square chucking different size bars?

What are your thoughts?

Gary


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## Ray C (Feb 1, 2013)

Gary... Haven't tried that but, what causes that problem in the first place is how accurately the jaws move in their slots and grooves.  I'll bet dollars to donuts that you can take a proof rod, mount it three times and each time you'll get different amounts of runout at different lengths.  If those jaws wiggle just a tiny bit as their being tightened, it influences the workiece.  There's a lot of clearance so the jaws can move freely and therein is the problem.

Sometimes the front teeth of jaws wear out from grabbing small pieces.  That throws things off but it can be corrected.

If you want to rid yourself of that age-old problem, spin between centers or spend the time/money on setting-up a good collet chuck.


Ray


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## GaryK (Feb 1, 2013)

Ray C said:


> If you want to rid yourself of that age-old problem, spin between centers or spend the time/money on setting-up a good collet chuck.
> Ray



Thanks Ray. Like I said it's more of a mental exercise than anything. Everything you said is true! I've always taken the faults of a 3JC into account when ever I use one. It's just
something you learn to deal with.

I have ordered a nice 6 jaw chuck today so I don't think I will be using my 3JC much anymore anyway.


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## Ray C (Feb 1, 2013)

Cool, what 6J did you get?  Would love to have one some day and want to hear about the models folks have and how they like them.

I ran myself ragged early on trying to square-up jawed chucks.  -There's only so much you can do and I ultimately figured-out that variability in lengthwise runout is mainly caused by the variability in how the jaws slide in their corresponding slots and grooves...




GaryK said:


> Thanks Ray. Like I said it's more of a mental exercise than anything. Everything you said is true! I've always taken the faults of a 3JC into account when ever I use one. It's just
> something you learn to deal with.
> 
> I have ordered a nice 6 jaw chuck today so I don't think I will be using my 3JC much anymore anyway.


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## GaryK (Feb 1, 2013)

Ray C said:


> Cool, what 6J did you get?  Would love to have one some day and want to hear about the models folks have and how they like them.



I ordered a Fuerda for $590 shipped. I have heard nothing but good things about them and I'll save hundreds over a Bison.

Gary


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## darkzero (Feb 1, 2013)

I use my 6-jaw most of the time and the TIR is so low that's the reason why I don't really see a need for collets now. I did keep my 3-jaw though. Alternating the pin positions, I got .008 on one, .005 on another & under .002 on the last position. This is where I centerpunched to mark the position. Being spoiled with .0002 TIR, what I did was turn the register on the backplate slightly undersize then skimed the face. With the undersize register & play in the counter bore for the SHCSs, this allows me to dial in the chuck to just under .0004" or so tapping with a hammer. I used a 1.5" dia Thompson linear shaft. Downside to this is a crash or bump could knock the chuck out of round. But I only use the 3-jaw for certain operations & I've never had this issue yet.

Again, those Fuerda 6-jaws do look nice! Looks pretty much exactly like my Bison & much nicer than the BTC chucks. The Pratts look even better but you will pay the price!


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## 8ntsane (Feb 1, 2013)

Gary

That is one sweet looking chuck you just purchased. I have looked at  the 6 jaw chucks many times, but usually the price is the killer for me. Seems like you got a pretty good deal on yours. I assume your working with thin walled tubing?

Ether way, nice purchase :thumbzup:


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## darkzero (Feb 1, 2013)

8ntsane said:


> I assume your working with thin walled tubing?



I went with 6-jaws cause I got into machining since I did a lot of flashlight mods. The thin plastic reflectors than just kept flying out the 3-jaw chucks were not a problem in the 6-jaw. Making thin walled sleeves was so much easier too. But there is the downside to the 6-jaws, they don't grip as well as 3-jaws & can't compare to 4-jaws. There's times where I full form knurl Ti & it slips.


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