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View Full Version : How do I know my lathe straight?



Tommo
02-17-2018, 12:32 PM
I have an Atlas 618 I've had for a few years now and I've made a bunch of stuff on it. I recently was turning something that took up the entire length of the ways and I had a steady rest all the way over to the right to support the work. I first indicated the workpiece in a 4-jaw chuck, then set up the steady rest at the same place, and when I slid the rest down to the other end the fingers of the rest weren't hitting the way they were when I had it set up over at the left side.
How do I check to see if the ways aren't twisted/bent/worn or check to see if the spindle is even straight?

Erich
02-17-2018, 01:16 PM
A precision level placed across the bed can show if the bed is twisted.

The true test is to chuck up a large diameter piece of Al about a foot long.
Turn a relief in the center so you end up with two collars, one next to the chuck, the other at the free end.
Do not use a center in the tail stock to support the end.
Now turn each collar at the same cross feed setting.
Try for a .005 to 0.01 inch depth of cut, use power feed for consistency.
Measure diameters. If same, celebrate everything is perfect.
If cutting taper, shim front or rear of tailstock end mount to correct the twist in the bed. Can't remember which way to twist to correct which direction of taper.
This is an iterative process.

I don't know the details of the atlas lathe, but on my southbend, the headstock is fixed onto v ways in the bed and therefore has no possibility to be adjusted, short of removal and scraping.

Tommo
02-17-2018, 01:25 PM
Oh, so like a 1" collar at either end?

MattiJ
02-17-2018, 01:36 PM
1 inch for smaller lathes is good.
For 1 inch bar make the test collars not more than maybe 5 inches apart.

Gary Paine
02-17-2018, 03:07 PM
The Atlas 6 inch headstock is registered between the ways and should be in line. I suspect that the work as clamped in the chuck is just a bit out of parallel with the bed due to a small burr or imperfection in the workpiece or jaws or even a chip. I think you are describing a situation where if you revolved the work in the chuck the end of the work moves in a circle.
That is not abnormal at all, as any little bit is amplified a lot on a long workpiece as you describe. What you say you did is all correct in setting the steady up by the chuck and then moving it, but you should move the steady and slip the piece into it BEFORE tightening the chuck on the work.

Tommo
02-17-2018, 04:19 PM
Okay. So if I indicate a piece, then set up the steady, loosen the piece in the chuck, move the steady, tighten chuck?

Gary Paine
02-17-2018, 05:26 PM
Okay. So if I indicate a piece, then set up the steady, loosen the piece in the chuck, move the steady, tighten chuck?

Yes