Two Collar Test

[Scra99tch]

So my central machinery 12x36 Lathe has a taper when cutting. I am trying to make a new cylinder barrel for my 1954 TWN Super Tessy and the .003 over 6" is not helping. Anyways when I did my two collar test I was getting about that over 6". I tried adjusting with shims underneath the foot.

First I started off with a .01 shim and had no change. Then I gradually increased it up to .06" still with no change. I finally found a wedge and tried that. Turns out my stand was just pulling off the floor so I loosened everything up again and figured if I want to get the twist back out of the ways best bet would be to anchor the stand to the floor.

I decided then to borrow the test bar from work that fits into the collar for my headstock. This also shows a .006" taper over about a foot. I then mount my chuck and flip the test bar and get about the same.

So is it safe to safe my headstock will need adjustment first and foremost.

Here are the steps I think I should take before the 2 collar test.

Take the rubber mounted feet that were put on the lathe off and use HD bolts to level the cabinets to the to the floor.
Level the lathe with a machinist level to the best I can get.
Loosen four allen heads that hold the headstock and tap it in to indicate zero on the test bar.
Then take to the 2 collar test and start shimming. Maybe leave it under tension for a few hot and cold days and retest. If not moving then anchor cabinets to the floor.

 

[verbotenwhisky]

So my central machinery 12x36 Lathe has a taper when cutting. I am trying to make a new cylinder barrel for my 1954 TWN Super Tessy and the .003 over 6" is not helping. Anyways when I did my two collar test I was getting about that over 6". I tried adjusting with shims underneath the foot.

First I started off with a .01 shim and had no change. Then I gradually increased it up to .06" still with no change. I finally found a wedge and tried that. Turns out my stand was just pulling off the floor so I loosened everything up again and figured if I want to get the twist back out of the ways best bet would be to anchor the stand to the floor.

I decided then to borrow the test ba from workr that fits into the collar for my headstock. This also shows a .006" taper over about a foot. I then mount my chuck and flip the test bar and get about the same.

So is it safe to safe my headstock will need adjustment first and foremost.

Here are the steps I think I should take before the 2 collar test.

Take the rubber mounted feet that were put on the lathe off and use HD bolts to level the cabinets to the to the floor.
Level the lathe with a machinist level to the best I can get.
Loosen four allen heads that hold the headstock and tap it in to indicate zero on the test bar.
Then take to the 2 collar test and start shimming. Maybe leave it under tension for a few hot and cold days and retest. If not moving then anchor cabinets to the floor.

Best advise I can give you is take it slow, a little at a time.... Make certain the ways are level using a machinist level before resorting to adjusting the head.

 

[Ulma Doctor]

Have you tried a deflection test?
Simply put chuck up a rod with relative girth ^ of 1” or better and about a foot long .
Mount a dial indicator to measure chuck movement while lifting and pressing down on the rod chucked up.
This will help determine if the spindle is adequately adjusted

 

[Scra99tch]

Have you tried a deflection test?
Simply put chuck up a rod with relative girth ^ of 1” or better and about a foot long .
Mount a dial indicator to measure chuck movement while lifting and pressing down on the rod chucked up.
This will help determine if the spindle is adequately adjusted

I have done that in the recent past. Got the adjustment to about a .0015 that was on a cold spindle though.

 

[gard]

I think you are on the correct path, level the lathe and use the test bar to adjust the headstock. With the test bar, you rotate the spindle and stop at the point that is 1/2 of the way between the highest and lowest readings. You should also check alignment along the top of the test bar, may need scraping or shims to fix if its out.
If you can get the test bar good in both horizontal and vertical directions, I do not think you need the 2 collar test or additional shimming.