I rebuilt my 1969 16" x 6' lathe some years ago with help from Ted!? Thank you Ted!? I bought it from work around 1990 - they had bought it new in 1969.? But it was not in great shape.? Ted provided many new parts and even quite a bit of labor.? I had set it up in the old shop and it cut pretty good.

Built a new shop a little over 2 years ago and finally got around to taking a test cut.? Started about 0.001" per inch.? The worst part is around the chuck area (no surprise) but worst is around 0.002" per inch.? But over 17 inches, maximum deviation is 0.013" .? From 0 to 17" its 0.0011".? I don't know what is typical, but this will work just fine for most of my needs.

What do you typically see from these lathes when? in nice shape?

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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

Ooops.? Over 17" max deviation is 0.0013"? Missed a zero.........
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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

Having problems with zeroes! Worst is 0.0002" per inch.? Missed a zero there too!? Its late.............? LOL!
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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

For sure deflection is a problem in the middle so I discarded the numbers that I felt would have been affected.? But the number I stated included everything but the actual middle.

In retrospect if I was totally serious about this I would cut a 2 1/2" diameter 18" long piece of aluminum and use it to minimize deflection.? Might actually do that at some point.? I started the testing by only cutting a 1" wide cut at the ends.? Once I was happy with that I did a full cut to get a better profile and eliminate tool position error from the DRO.

What do others do?
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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

Thank you Rogan!? That was very helpful in making me understand that I had a brain cramp.? I should of know better.? My tailstock center alignment was way off and really skewed my numbers.

I redid it with a 12" long 2 1/2" diameter aluminum bar without a center.? I did it just at the ends (9 inch measurement difference) and got it to measurement error.? I then skimmed the whole 9 inches and did a final cut taking 0.002" off the diameter.? Measured every inch over the 9 inches and every measurement was within measurement error (50 millionths of an inch or half a tenth).? I am shocked that its is that good.

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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

Assuming the twist is out of the bed here's an easy one to set the tailstock.

Say the diameter of the? quill in the tailstock is 1.4985 inches.
Turn a short piece of metal in the chuck to that dimension.
Put the tailstock at the far end and lock it down.
Set up a dial indicator in a tool post and zero it on the piece you turned to 1.4985.
Run the carriage down and put the indicator on the tailstock quill. It should read zero.
Now you just tweak the tailstock alignment screws until it reads 0.
You don't need an x feet long bar to work with, just a 1 inch stub of scrapbinium.

开云体育

.0002" taper sounds pretty good on a 55 year old machine.

What are you trying to test because your setup has at least 5 variables?

To be clear once I used the 2 1/2 inch bar and skimmed the final coat, over 9 inches I got measurement error.? So roughly within 0.00005".? That is crazy good for a machine like this.
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1969 16" x 6' South Bend Lathe
Garage full of old Mopars........

Brilliant! I'd planned to do the two collar test and the 12" long cut test, but I'm going to add this one to the list, probably at the beginning. Still have to mount my chuck, making the back plate this week.