"Mounting a square piece between centers

[EOsteam]

OK, I have to mount a 1/2" square shaft 6" long in the lathe between centers.

1) Assuming one starts with a 4 jaw chuck how does one center a square piece in the 4 jaw chuck especially one that is only 1/2"?
2) Most of the shaft is to be turned down to 1/4" round except for one end which will be left square". Does one mount the traveling steady after the corners are turned off or do you wait until you are almost on dimension?
3) Would this be turned between centers or would one leave the end that is to remain square in the 4 jaw chuck?

Thanks,
HJ

[liveaboard]

Much depends on how much accuracy is required.
Centering a square is a pain; I put a dial indicator and measure each flat, lifting the plunger carefully by hand to rotate the work.
Of course it's never really square.

[epanzella]

I would center drill both ends of the shaft then dial it into to 4 jaw with 3" projecting out and the far end in a live center. Turn down what's exposed to 1/4" then project more out of the 4 jaw with the other end in the live center and turn again until you get where you're going.

[ALCOSTEAM]

If you have a mill I would set up the piece and indicate it in and then center drill, repeat other end.
Or if you have a collet set up there is always using a square collet.

[BadDog]

I had a similar issue some years ago. My required accuracy wasn't high, so I just faced it and looked at the pattern. Adjusted until the flats were as close to all on the same circle as possible, and just got on with it.

[Harold_V]

One consideration that will determine an acceptable procedure would be how straight the piece must be after being turned. You can expect movement as it is reduced in size, and it won't be straight unless it is free to move about. Turning between centers permits that to happen, while gripping in a chuck and restraining by tailstock (a center) does not. Holding a long, slender item in a chuck, supported on the opposite end by a center is almost a guarantee that the piece won't be straight, although there are ways to achieve acceptable results. Also, depending on how rigid your tailstock is, there's a risk of the turn ending up not concentric with the tailstock center if you grip by chuck.

I am not a fan of turning between centers. It tends to be rather chatter positive, but there are times when you may not have an alternative. When to introduce a follower would be determined by the problems you have in turning. For such a slender item, I suspect that it will be just as soon as you can.

A cylindrical grinder would make the task easier, with a centerless grinder making it a non-issue.

Just sayin'

H

[earlgo]

As an alternate, one could use a piece of round stock, turn the shank to the proper size and length and then set up and mill the square portion. That way it would be centered and square. Just another way of looking at your problem.
--earlgo

[whateg0]

Here's one video (of many) that explains how to indicate square stock in a 4jaw. This works for rectangular or hex or whatever stock, too.

https://www.youtube.com/watch?v=tVvuFTI0ygM

Dave

[whateg0]

FWIW, sometimes I cheat and take a piece of stock that is already the right diameter and weld a chunk onto the end that can be machined to the right size. No, it's probably not the "right" way to do it, but sometimes, it's right enough.

Dave

[pete]

As already mentioned it depends on the accuracy required. Also just what equipment is available. 6" isn't very long and if you've got a vertical mill and an angle plate the shaft could be accurately measured and then hung off one of the table edges while indicated vertical and clamped to the angle plate for the center drilling and then doing it by edge finding and co-ordinates. One of those pita jobs where the set up takes a 20 minutes for 60 seconds of machining time. But 6" long is starting to move into where I'd use my lathes milling attachment even tho I've got a vertical mill. If I had a horizontal mill I'd chose to use that for the center drilling since it would be fairly fast and easy.

One old trick to indicate non round stock in a lathe's 4 jaw is to add a light piece of sheet metal between the indicator tip and the work. Even a cut up beer can works. That saves having to retract the indicator tip as it passes each corner on the work. Figuring out how to hold that sheet metal in place is the only problem. I've used the standard magnetic indicator base and arm assembly or even C clamped one end to one of the lathe tool holder bolts. It just depends on what's fastest and easiest to figure out. Getting the part concentric to the lathes C/L in a 4 jaw is only half the job, getting it true to the lathes way's plus concentric at the same time complicates the issues. Even more so if your chuck jaws aren't in perfect shape and square to those ways. It can be done, but my bet is there's far faster way's just to get each end accurately center drilled. It also might be easier to machine the whole part from slightly larger round stock, get the shaft dimension's correct for length and diameter, then just mill the O.D. back down to your 1/2" square dimension. That's probably how I'd do it for something of that size. Yes you waste a bit more material, but the whole job is likely to end up easier and faster.

[tornitore45]

If it was my project I would silver solder the square part on a piece of 1/4" drill rod or a ground and polished shaft if that is required for accuracy.

[GlennW]

I just did a similar job and cheated. I used a square collet.

1/2" square 8 1/2" long turned down to 3/8".

I do this stuff to remind myself that I don't like doing this stuff...