Which position to tighten the three jaw chuck?

[Net30]

Number one or number two and why? I normally default to the one with two supports on the bottom, but maybe I'm wrong. I've never seen anything said about it ever.

#1


#2

 

[GrifterGuru]

Phot 1. It lifts the stock whilst the other two jaws close in from above. You can watch it does not snag between two jaws.

Just the way I do things with a 3J.

4JSC and 6JSC can be treated the same within reason, but a 4J IP is a different matter......

 

[Smithdoor]

Number one or number two and why? I normally default to the one with two supports on the bottom, but maybe I'm wrong. I've never seen anything said about it ever.

#1
View attachment 476566

#2

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Any works.
They have three as some lathes are hard to turn and is faster to have three spots.

Dave

 

[Smithdoor]

Number one or number two and why? I normally default to the one with two supports on the bottom, but maybe I'm wrong. I've never seen anything said about it ever.

#1
View attachment 476566

#2

View attachment 476565

A three jaw chuck scroll is worn the three jaw is not very accurate.
The scroll bearing needs to be under 0.000,1" clearest to a good chuck.

Machinist on a used chuck will use brass hammer for more accuracy.

Dave

 

[GrifterGuru]

A three jaw chuck scroll is worn the three jaw is not very accurate.
The scroll bearing needs to be under 0.000,1" clearest to a good chuck.

Machinist on a used chuck will use brass hammer for more accuracy.

Dave

Give the jaws a knock, go around tightening, then once more just to be sure. I do that myself.

Can also be used as a form of tap true. tap one jaw in particular to "nudge" the stock being held. Really depends on condition of the teeth of the jaw and the scroll.

 

[jwmay]

The most important consideration when it comes to this is which way your own toes are pointing. It’s nearly impossible to get the jaws to close correctly if your toes are pointing to the bathroom door stall, or a table leg in the break room. If your toes are pointing generally perpendicular to the lathe, and within 14” of it, the chuck jaws usually tighten up just fine.

 

[55fairlane]

I think your over thinking this.....when I served my apprenticeship we were taught to hold the stock while twisting the key, give the stock a slight jiggle as the jaws close. This will help the jaws seat. If your that worried about things, use a 4J , use a collet or bore a set of soft jaws.

 

[RaisedByWolves]

I think your over thinking this.....

I get a kick out of some of the strange things people here concern themselves with.

I believe some of the setups I’ve done over the years would cause some posters an existential breakdown.

 

[f350ca]

As a side note.
On a quality chuck, one of the pinions will be marked, usually with a 0. That is the one they used when grinding the jaws. If you use it you will get the least runout.
Unless the chuck is totally worn out.

Greg

 

[MrWhoopee]

If you're concerned, rotate the chuck as you go, tightening each pinion in turn.