Do You Use a 3 Jaw or a 4 Jaw Chuck?

[Glenn Brooks]

An old time machinist taught me how to make work perfectly concentric in a three jaw. Now I hardly ever use my four jaw. Set up the work a little loose - not much - in a three jaw. Then turn on the lathe at slow speed, say 100 Rpm. As it wobbles around, tap the high spots with a light hammer, or length of steel. After 2 or 3 taps, you’ll get the piece perfectly concentric, usually well under 3 thou. Tighten the jaws and make your part.

Works every time. I hardly ever use my four jaw anymore, except when I have some odd shaped work. They all sit there collecting dust. This is the way machinists used to set up work before precision DTI’s were invented.

Glenn

 

[MrWhoopee]

An old time machinist taught me how to make work perfectly concentric in a three jaw. Now I hardly ever use my four jaw. Set up the work a little loose - not much - in a three jaw. Then turn on the lathe at slow speed, say 100 Rpm. As it wobbles around, tap the high spots with a light hammer, or length of steel. After 2 or 3 taps, you’ll get the piece perfectly concentric, usually well under 3 thou. Tighten the jaws and make your part.

Works every time. I hardly ever use my four jaw anymore, except when I have some odd shaped work. They all sit there collecting dust. This is the way machinists used to set up work before precision DTI’s were invented.

Glenn

This is how I learned to do it, with the exception of rotating the chuck by hand and gradually tightening as it gets closer. We never used a 4-jaw for round parts unless you needed eccentricity. Much easier than changing a 12 in. chuck.

 

[Bobby Bailey]

Perfectly concentric is in the eye of the beholder. LOL Within .001 is almost10 times too big for us and is why we don't use a 3 jaw. And even if it was acceptable for our work, tapping the 3 jaw around is slower than just dialing in a 4 jaw to start with. 4 jaws are fast once you use them.

 

[MrWhoopee]

Perfectly concentric is in the eye of the beholder. LOL Within .001 is almost10 times too big for us and is why we don't use a 3 jaw. And even if it was acceptable for our work, tapping the 3 jaw around is slower than just dialing in a 4 jaw to start with. 4 jaws are fast once you use them.

Yes, if you need to hold tenths, particularly on multiple parts, a 3-jaw is not the best choice . But then again, this is a hobby site. Few of us need to hold tenths, nor do we have machines that will. Indicating a 4-jaw might be faster. I say might because tapping in a 3-jaw can be quite fast and only requires tightening one adjustment, not four. Just getting a 4-jaw within the initial runout of a 3-jaw will usually take longer than getting the 3-jaw within .001. If you have to put the 4-jaw on the lathe first, then it's no contest. A lot of times, whatever is on the lathe when you walk up to it determines what is fastest. And, of course, in a hobby shop situation, ease, not speed, is the primary consideration.

If I had neither, I would get a 4-jaw because it is more versatile. Having both, the 3-jaw gets much more use (and the collets more yet).

 

[dtsh]

I have only the 3 jaw that came with my lathe and for now it supports all the work I do on it, which is admittedly not much. I plan to get a 4 jaw eventually because some of my future projects can utilize it and I look forward to having the added flexibility of what I can do with it, but until those projects get closer I can't justify getting one. If I could have only one chuck, it'd be a 4 jaw and a collet block.

 

[chips&more]

I just read all of this thread. And I wonder how my folks have used a really nice 3 jaw chuck? I’m not selling them! But say, like a Buck set-tru. IMHO, I think your 4-jaw (except odd shapes) and collet stuff will collect dust after you have tried one…Dave

 

[MrWhoopee]

I just read all of this thread. And I wonder how my folks have used a really nice 3 jaw chuck? I’m not selling them! But say, like a Buck set-tru. IMHO, I think your 4-jaw (except odd shapes) and collet stuff will collect dust after you have tried one…Dave

My 3-jaw is a Buck Ajust-Tru. It's a beautiful chuck and runs dead nuts without having to adjust it frequently. I still prefer collets if the stock size permits.

 

[NEL957]

I put a 8 inch 4 jaw on my 10K and after using it I'll never go back to 3 jaw. I also made up a ER 32 collet holder when I need the accuracy.
I read some where about the lathe walking, turn the damn speed down. Not everything runs 3000 rpm's
Nelson
As far as a Tru-chuck, you can not turn a square block.

 

[Pro70z28]

I use the 3 jaw unless the part doesn't start out round or needs an offset.

 

[Bobby Bailey]

Yes, if you need to hold tenths, particularly on multiple parts, a 3-jaw is not the best choice . But then again, this is a hobby site. Few of us need to hold tenths, nor do we have machines that will. Indicating a 4-jaw might be faster. I say might because tapping in a 3-jaw can be quite fast and only requires tightening one adjustment, not four. Just getting a 4-jaw within the initial runout of a 3-jaw will usually take longer than getting the 3-jaw within .001. If you have to put the 4-jaw on the lathe first, then it's no contest. A lot of times, whatever is on the lathe when you walk up to it determines what is fastest. And, of course, in a hobby shop situation, ease, not speed, is the primary consideration.

If I had neither, I would get a 4-jaw because it is more versatile. Having both, the 3-jaw gets much more use (and the collets more yet).

Hobby site or not, it is about imparting knowledge and I believe you would agree on that. There is no reason a hobbyist can't learn or improve from a non-hobbyist or the non-hobbyist from a hobbyist.
My comment is not that you should not use a 3 jaw if that is what one likes. It is rather about; so many guys, especially new guys avoid a 4 jaw thinking the 4 jaw is hard to use, hard to learn, and too slow. When none of those things are true.
Using two chuck wrenches, 180 dregrees apart, one can dial in a 4 jaw with just a few revolutions to 0.0005, a couple more revolutions and its down to a couple of tenths. Its fast and easy. I just want new guys to see that the 4 jaw isn't really scary or slow or hard to use.
"And, of course, in a hobby shop situation", the 4 jaw can meet both ease and speed, they are not mutually exclusive things. Its about learning and trying new things to expand ones skills.

Having equipment to hold accuracy is not hard for a hobby shop. We run two South Bend heavy 10's and a South Bend 10K. All three are considered by many to be hobby shop size and all three are accurate. Clock making, model engine building and gunsmithing all benefit from it, and I do know many hobbyist that do worry about holding tenths.

As far as putting the 3 jaw on the lathe, I'd have to dig in the back of the cabinet to get the 3 jaw and then clean it. LOL