I had an emergency job lastnight, turn 1 15/16in journels 8.0in long on 2.5 X 2.5in square stock, 316 S.S, and key one side 4.5 long. I've never needed to turn square stock before so I did the only thing that occured to me at 2am, set the stock in the chuck placed a precision level on the top and turned chuck until it read 0.0 and indicate face to opposite face. After completing one I flipped the stock and to keep from marring the journel I chucked on the square again and repeated.

Everything turned out fine, shaft installed, runs true and salesman called in with PO for 2 more to go to their storeroom but I just feel like I half @$$ed it a little.

What is the "correct" method for indicating square stock in a 4 jaw chuck?

Should I have turned a center in the chuck and driven the shaft (40.5in long) with a lathe dog to ensure the shaft ran true or is indicating as I did considered ok?


Thanks
Scott

Indicating as you did is good, but should have been done twice instead of using the level. Will work perfectly fine for your conveyor shaft though.

I suggest
1-Hold the bar with about an inch sticking out of the chuck.
2-Indicate it right at the end face.
3-Center drill
4- move bar out of chuck lets say 1 foot (unless your journal is longer)
5-with the end supported in your live center indicate the square bar right beside the chuck.
6-turn
7-repeat for other end
8-If you need to be extra accurate you can leave stock and turn between centers.

This method should be more axially "true" than using a level.

Indicating as you did is good, but should have been done twice instead of using the level. Will work perfectly fine for your conveyor shaft though.

I suggest
1-Hold the bar with about an inch sticking out of the chuck.
<SNIP>


Thanks DareBee. I thought to take a test cut and check the tail stock, adjusted it to .0005 run out over 12 in (journal was 8.0) which was as close as I could get it to true with a short piece of stock. If I'd have faced and cntr drilled close in that would have made my life easier this AM.

One question though, I noticed approx -.030 difference when the level read +/- .1 degree. Would you just watch the indicator and note the high reading as it passed level? That was why I ended up throwing the level up on the stock was to try and get as close as possible to a reading at 180deg rotation. I should have stated I had the level running in X to get as accurate as possible 180deg rotation when moving from face to face.

I see what you were trying to do, very very difficult that way.
I like to bring the indicator in from above - centered vertically (by eye) on the Z axis. Set it on a flat side. Gently rotate the chuck back and forth a bit - the indicator reading will bottom out and start going up again - take note of what number it bottomed out at.
Now carefully pull the plunger of the indicator up to clear the stock (1" stroke indicator is best here).
Rotate the stock 180 and carefully let the plunger back onto the stock. You don't want to be moving any handles or pulling the indicator stand around will doing this.
Move chuck back and forth to get "low" reading again.
Now adjust the chuck to be half way between the 2 readings.
Keep repeating all around the part over and over.

Do not worry about sides 90 degrees apart not giving the same reading. Theoretically they should but stock is not perfect.
You should easily be able to get opposing sides within 1/2 thou of each other.
Sound like a bit of pissing around but when you get good at it it goes very quick.

I have never heard of a tailstock that can be adjusted for runout?
Do you have a set-tru chuck in the tailstock or something?

Darebee's horribly tedious procedure is the way I have done it just with the change that I crank the cross slide out and back to rotate the stock rather than pull on the dial plunger.

I disagree with the "it goes very quick" unless your definition of quick is very slow. :)

Darebee,

OK we did the same thing exchanging level for watching the indcator and indicator position. I noticed .008 difference from side to side as opposed to top to bottom, but it indicated to it's opposite so... The tailstock on that lathe ends up with an offset from CLX after you unlock it and move it. Wrong term, runout? Anyway I'm checking for a taper in the stock and adjust as needed, which is pretty much every time I use it on this paticular lathe.

Geoff,

I'm glad I wasn't to far off in what I was doing at least, stock for the next two shafts should be in the first of next week. So I guess other than the tooling I ordered this morning I'm ready to go.

Thanks to both of you for the help.

Practice makes perfect (I guess).

I can do this "I like to bring the indicator in from above - centered vertically (by eye) on the Z axis. Set it on a flat side. Gently rotate the chuck back and forth a bit - the indicator reading will bottom out and start going up again - take note of what number it bottomed out at.
Now carefully pull the plunger of the indicator up to clear the stock (1" stroke indicator is best here).
Rotate the stock 180 and carefully let the plunger back onto the stock. You don't want to be moving any handles or pulling the indicator stand around will doing this.
Move chuck back and forth to get "low" reading again.
Now adjust the chuck to be half way between the 2 readings.
Keep repeating all around the part over and over.
end quote

I am less than 5 min per cycle on 4" stock in a 36" chuck.
I spent a lot of time on a 4 jaw many years ago.

If you set your indicator horizontally, you can use two keys to center the stock in about three iterations (measure, adjust, check).

Aaron

Practice makes perfect (I guess).

I can do this "I like to bring the indicator in from above - centered vertically (by eye) on the Z axis. Set it on a flat side. Gently rotate the chuck back and forth a bit - the indicator reading will bottom out and start going up again - take note of what number it bottomed out at.
Now carefully pull the plunger of the indicator up to clear the stock (1" stroke indicator is best here).
Rotate the stock 180 and carefully let the plunger back onto the stock. You don't want to be moving any handles or pulling the indicator stand around will doing this.
Move chuck back and forth to get "low" reading again.
Now adjust the chuck to be half way between the 2 readings.
Keep repeating all around the part over and over.
end quote

I am less than 5 min per cycle on 4" stock in a 36" chuck.
I spent a lot of time on a 4 jaw many years ago.

I do it like this too, except mounting the indicator vertically seems too clumsy to me, I mount it in the horizontal position on a rigid stand, eyeball the indicator tip to the center of the stock, it doesn't have to be perfect. I bet I could indicate in a square bar at 1 point within .001 in less than 2 min. But I've been doing 4-jaw work for over 20 years too.

Hi, I also do it like Darebee, but I also have a flat plate that I lay across the bed and use a square to get the front face of the job vertical, then just put a dial indicator on my surface gauge and run it across the top of the job from the back, rotating the chuck to get the other side and split the difference when adjusting the top and bottom jaws.
When I worked in UK I had a square job weighing several tons in one of those big faceplate lathes.
The only way to move the faceplate chuck was with the pendant control from up on the toolpost.
You started off by measuring the distance from the outer edge of the chuck to the job with a tape or 6 ft rule, and adjusted the jaws till you were close.
Then depending on what you were doing, IE, cutting down from a rough forging or casting, or if it was setting to a finished diam or face it would be close enough, you would then use the graduations on the top slide to wind in and out to get more accurate, turning the chuck with power to get the four planes.
Barring the chuck round was not an option as it took two to do it, one to move the chuck and one to get the position.
I used one crafty method, by marking a chalk line on the bed and moving the chuck to the four points respectively and marking the "cardinal" points on the chuck face in chalk.
Using this method required a dial indicator on a tool holder on the top slide so that the crosslide could be wound in and out under power while you barred the chuck round to the four points, and allowed you to see the zero from down on the ground.
Ian.

Thanks to all. I feel more confident in making this next batch for their stores. Hopefully the metal will be on the truck this morning so I can go to it at a decent hour

Scott