Do I need a precision machinists level?

[Steevo]

I have leveled my lathe bench in both planes with a bubble level, then placed my lathe on it and am ready to fine-tune the level of the lathe bed.
I read the original manual and they state that you need to use a machinists level with .0005"/ft accuracy to level the lathe.
I have a digital (SmartTool) level that is accurate to 0.1 degrees, but that is a far cry from .0005"/ft.

 

[Conrad Hoffman]

I'm going to say that a Starrett 98 or one of the cheap import levels is sufficient. What you want to do is start with the bed straight. It's really bad to just apply the test bar method and turn the bed into a pretzel to correct some real or imagined fault. Trying to correct more than a very small error by twisting the bed will cause excessive wear and not really get you where you need to go. You may also use the level more than you think. Wood changes with age and humidity and floors too. My cement garage floor actually warps with the seasons and the water table enough to mess up the lathe performance. I re-level several times a year.

 

[AR1911]

As Conrad says, level is secondary to straightness.
Neither a lathe nor mill has to be level, or you would never see one in a ship's machine shop.
But by starting out level, you have a very good baseline to achieve a straight lathe bed.

for a mill, a level bed makes setups easier.

 

[Tony Wells]

Need versus want, more or less. You can do just fine with a good quality standard level. I have a precision level, and use it periodically, and I have a Wyler inclinometer, like this one, but a little older:



http://premiummetrology.com/index.php?controller=product&path=21&product_id=8
(No, I didn't pay that for it, but did some horse trading) It's good +/- .01 degree.

 

[Steevo]

Ok, I got it this far, and will use it a while to see if there are any signs of twist or other anomalies:

 

[Tony Wells]

Steevo, you should be good to go. I always flip the level I am using 180 deg to see if there is any different to be split. In calibrating a level, that's part of it anyway. So, if you get a zero both ways, that's as good as you can get, with any level.

If you have a large (1" or so) ball bearing, see if it will stay put if you place if on a flat area of the ways. It's crude, but if it rolls away, you aren't dead on level.