Centering Work in a 4-Jaw Chuck

[trevj]

I think that's a bit too optimistic for someone new to the process. But it's a reasonable goal. In other words don't expect to be able to dial a part in very quickly at first. But after you understand what you are doing and let it become instinctive, it should not take more than a minute or so to do.

In the beginning, I think its better to take the time to understand the process than it is to try to go quickly.

Indeed, and not intended as an immediate goal. But not having done on in a while, my bet is that it would take me more time to find my indicator and base, than to set up a random round object in the chuck, and get it dialed in!

4 jaw chucks, and thread cutting/grinding a threading tool, are the two things that I see, and saw, a LOT of guys get all worked in a lather over, and there is no good reason for either to be an issue.

 

[a smile]

Hope I'm not overselling something dead simple. All I made was 2 identical chuck keys. They are shorter & more compact than the typical regular key so its comfortable to position your hands on either side of the 4J chuck (horizontally in a lathe vs up-down). Just insert them into the opposing key registers & rotate simultaneously. Obviously to displace the work they turn in reverse direction to one another dictated by the jaw screws, but your brain figures that out really quick. As you feel it tighten against the work you crack one open & tighten the other nudge-nudge mode. Everything else about dialing in is no different than regular 4J setup.

On initial setup setup, what I find is you can get real close if you just focus on the gap between an indicator tip positioned say 1mm away from work. Don't even look at the dial at this point. Just make the gap the same between the 2 jaw axis lines rotating 90-deg. You eye is amazingly good at distinguishing a gap. Then when you apply the indicator to the part, the needle will exhibit much less movement & center will be much more obvious. If its counting 2 revs one way or another (out by a lot) just drives you batty & wastes time. Using the reference circles in the chuck relative to jaws is another good initial visual

This is an efficient method!

 

[Dabbler]

I really like using my twin, mini chuck keys on 4J.

What a great idea!

What RobinHood says about over torque is exactly right. You can see this being done by many YouTube <cough> pros.

exactly!! - and don't get me started on people who crush parts in their milling vises!!!

And yet centring in a 4j is a necessary, basic skill that needs a lot of practice to master. My mentor showed me *once* without any explanation, and said "and now you know". I had to teach myself. Prolly many of you are far better than I at it, but i have my way, and it doesn't take so long that I'm frustrated at the end. Good enough.

-- but I think it might be time to make those two keys - that looks intriguing!

 

[FatherWes]

I'm late to the party, but can relate to comments about which way is high...

I usually reach in and manually stroke the dial gauge to confirm which direction is high. Takes a second and provides instant confirmation.

I also like the idea of leaving the 4J in the machine so I have to practice. Although I did put the 3 jaw in the other day because I was trying to true up a large (for me) 2 inch diameter bar that was too long to support from just the chuck. Using the 3 jaw took care of centering the one end while I got things centered and supported on the free end.

 

[Susquatch]

I usually reach in and manually stroke the dial gauge to confirm which direction is high. Takes a second and provides instant confirmation.

I confess I sometimes do something similar. It's especially important when using dial test indicators (the ones with a little swinging needle at the business end).

Anyone easily confused shoud stop reading now. For the rest, read on.

Indicator holders are fairly stiff, but not at all like the work piece or the tools. Instead of moving the plunger, I lightly push the indicator holder and indicator toward the work. That has the same effect as pushing the plunger toward the indicator but its a whole lot easier to do. You just have to remember that moving the indicator has the opposite effect as moving the indicator rod. It's easy to remember if you think of either one as pushing them together.

Earlier I said that it's even more important on dial test indicators. That's because the polarity can be reversed on some models so even a seasoned machinist needs to check which way they are set every so often.

 

[Dabbler]

So my 'secret sauce' is to do the reverse of all the experts out there. My gross adjustment is done at the unsupported end of the part.

That way I can push (or pull) the part to deflect my indicator. It *reassures* me. Then I get it roughly to centre at the end. I will then go inboard, and get it the way I want it. Then outboard, rinse and repeat.

This way it is never more than ?5? minutes (I've never timed it) and usually much faster. Faster than my mentor, anyway (I can be very competitive)...

 

[trevj]

I'll let y'all in on a funny secret!

I'll ram a piece of stock into a three jaw chuck, and go to town on it, way sooner than reach for a four jaw chuck.

I have it, I use it regularly, and it can be your ONLY chuck, pretty easily, but I also understand when it might not be the fastestest, easiest, choice!

I just know, that you need to have stock, larger than the finished diameter of the final part, and that you need to be able to do as many of the required steps as possible that relate to concentricity, in one operation, without removing the piece FROM the three jaw chuck!

Once you take a skim off the outside of the bar, your stock is as centered as it can ever be. Unless you release it from the grip of the chuck!

So, understanding the series of processes, that are required, to reach an acceptable end result, is the entire key, to being able to make a great part, out of lousy stock in a lousy chuck!

I LIKE my four Jaw Chuck, but my Three Jaw scroll chuck is faster and easier to use, much of the time, esp. when the bar being used as stock, is large enough to allow a skim pass to true it up, AND the part can be almost completely made, in one set-up!
But, you must have a pretty solid grasp of the sequence of operations, to get from bar to part, first, so as to be able to plan the operations, to NOT, back yourself in to a corner!

How do I get from here to there?

How do I support the part while it undergoes knurling?

Which Operations are hardest? Should I do those first, so I can start over sooner, or do I leave them until I have considerable effort invested, and THEN put my part at risk?

Every part made, is a series of simple operations, no matter how the end product becomes complicated. Turn a diameter. Place a shoulder or shoulders, in the correct place. Create a thread. Champhers. Counter-bores. Recesses. Material to support the work with a center, while it gets beat on by a knurl tool.

A fella has to be practical sometimes. When you understand how you are getting from 'here' to 'there', you get to map out the trail you will take.

There is seldom only ONE path, that will get you to the end goal. You can do it this way, or that way, and they are both (all!) correct, if the end result is a part that fits where it is needed, and does what it should!

And that's me waxing philosophical, for tonight! LOL!

 

[Former Member]

Over the years a 4 jaw was seldomly used because of the effort required to set up, a few years ago I needed to do a lot turning on slightly out of round stock that needed to be turned center, so it got easy all of sudden and I reach for the 4 jaw more often.

Who knew practice makes it easier. .

 

[Susquatch]

And that's me waxing philosophical, for tonight! LOL!

Good philosophical wax job.....

What I notice most of all in those new to using a lathe is the need to understand the inherent concentricity of a lathes spindle. Concentricity is the heart and soul of a lathe - its what a lathe is all about. Once a machinist understands that, they also quickly understand why your point about a 3 jaw and a skim pass is so totally spot on.