Three Jaw Chuck--Tighten All Three Sockets?

[npalen]

I've seen, over the years, guys tightening a three jaw chuck using just one socket and others using all three sockets. Which is the correct method and/or which yields the most accurate results?

[DrMike]

Yup, you are supposed to tighten from all available sockets.
Same thing on Jacobs chucks, tighten from all available locations.
That's supposed to provide the most uniform, even pressure around the chuck.

Unless I have something really expensive (in time or money) in the chuck, I don't do it either.

[BCRider]

Seen it, never done it at all. And never had an issue at all.

Also after some trials I found that my 3 jaw produced less runout with one particular socket than the others. I've marked and use that socket pretty consistently for use on parts that already are machined and I want to get a pretty good runout number. For raw stock I just use whichever is on top.

I think it might be a "thing" if one were after the most possible grip available? But other than some crazy big item held on outside jaws where there might be interrupted cuts I've never seen the need. Or if I were doing a multi hundred pound long tube or shaft like Curtis at Custom Edge Engineering I think I'd go around the clock on each socket for something like that. But otherwise I've never had an issue.

On the bulk of our work that is done on round bar it does not take a whole lot of torque to give a perfectly good grip. For example, gripping a bolt to do a little light shaping work on the heads. Who hasn't just grabbed the threads in a gentle but firm grip that holds just fine without bruising the thread crowns? And it held just fine. So it really doesn't take a whole lot of force to hold most things. In fact I'd suggest that if we go max gronk on all items all the time that we will end up causing more wear in the shorter term.

[old mart]

No, with all three jaw scroll chucks, if you do some tests, it will be found that concentricity is better with one of the sockets. This might possibly vary with work diameter, but you have to draw the line somewhere. The best results will tell you which of the three to mark with a small scratch or whatever so you always use that one. Undoing the chuck can be with whichever is most convenient at the time. Any position can be used with something which will not be rechucked after machining,a small error will not be likely to matter, unless the start diameter is the same as part of the finished size.

[DrMike]

As long as it is open season on things as simple as slitting saw holders...

If you are tightening your chucks with only one socket because once upon a time you found that gave you the least runout,
you might need to periodically check that sweet spot to make sure you aren't wearing it out with overuse.

[Doozer]

3 makes it tighter.
1 ( the master one) makes it accurate.
So take your pick.

-D

[old mart]

As long as it is open season on things as simple as slitting saw holders...

If you are tightening your chucks with only one socket because once upon a time you found that gave you the least runout,
you might need to periodically check that sweet spot to make sure you aren't wearing it out with overuse.

That is why I only make a small mark adjacent to the master socket.

[Mike Amick]

How do you know which one is the master ?

[Joel]

Trial and error - by measuring for the least runout.

[J Tiers]

It's almost certainly caused by one happening to move the scroll slop in the direction to counter the inherent runout from other causes, OR that particular one just having less slop overall.

It's odds on that the best will in fact change over time. If the scroll has slop then probably cutting forces can move it around, so you might want to do something about the scroll slop.

[rickyb]

How do you know which one is the master ?

My room came marked from the factory. Otherwise get your dial indicator out and test each one

[boslab]

I was taught that whilst you pull up the Chuck from a single drive socket that it was pertinent to take up the backlash on all three, as it’s better to have all three take the load and not have 2 rattling about, made sense.
mark

[A.K. Boomer]

3 makes it tighter.
1 ( the master one) makes it accurate.
So take your pick.

-D

Bottom line is if you actually have a "master" then you have an inferior chuck, so if you ever have the chance in using precision stuff the recipe goes something like this, Tighten with one, accept slight inaccuracy and looser grip, tighten with 3 and not only increase the grip but also the accuracy,

Keep in mind - not a machinist here I think the occupation is boring,,, (no pun intended) just a guy who know's machines and equipment very very well.... again - talking precision stuff...

[J Tiers]

At the end of the day, the chuck itself is not accurate enough to make a lot of fuss worthwhile. "As accurate as possible" (with that chuck) is probably not very accurate.

Most, if not all, of the 3 jaw chucks I have use just one pinion anyhow. So I can say "I just use one pinion", or I can say "I use all the pinions on the chuck" and it means the same thing.

If it is important, I use the 4 jaw.

[Paul Alciatore]

I would mostly agree with this.

But individual chucks can vary. If you want the best results you will have to experiment with yours.

I think that tightening all three will make it tighter. On some occasions, after tightening that way I have had to go around all three in order to loosen it. So definitely tighter. The idea seems to be that the scroll settles unevenly to one side when tightening from any single point. I suspect that the best results may be when it is gradually tightened with two or more cycles of 1-2-3 instead of just mashing down as hard as you can for just one round.

And there is always the possibility that using some other sequence may even produce better results. Perhaps a 3 then 2 sequence may produce the best accuracy. Or 1 then 3, or etc.

On top of all that, three jaw chucks are infamous for inaccuracies. One thing that contributes to this is UNEVEN wear on scroll. For instance a chuck that has been used for a lot of parts with a 1" OD may have extra wear at that position on the scroll. There could easily be one runout at that, 1" diameter point and other runouts at other diameters.

If you want the best results, you really need to experiment and know YOUR chuck.


OR, to always allow/get good concentricity with a three jaw, use one that has the True Set feature or one similar to that. I have added four set screws to my three jaw's back plate to allow it to be precisely adjusted.

3 makes it tighter.
1 ( the master one) makes it accurate.
So take your pick.

-D