[Metrology] Calibrating A Machinist Level

GM had a room (Department) known as "Perfex". There they had machines that could turn to millionths of an inch. The room was temperature controlled. If someone came into the room a loud alert went off. This meant that the temperature had changed enough to stop working till it came up again. Yes, you could turn to those tolerances and even closer. Super Mikes were the normal.

"Billy G"
 
I have leftovers from a old job that allow me to use laser interferometry for VERY precise distance and positional measurements in 3 dimensional space. The lasers output a 32-bit float (sixteen bits right of the decimal place, do the math). I don't use them for calibrating a lathe in a home shop, but I'm fairly certain I could cobble something together. But then like Bill inferred, I've have to put together a met station for meteorological measurements and move my shop to one of the fab cleanrooms at work.

For my personal usage I stick to tenths and have held to that over almost 20" of turning length. Until the temperature of the part and the room changed... :)
 
mikey said:
I assume you're talking about a Starrett 98-18. If so, go here and download the powerpoint entitled "Calibrating and Maintaining Your Level" near the bottom of the page:

http://www.goodson.com/technical-library/

It pertains specifically to the Starrett 98 and is very clear.
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That is what I have. I will try this method.

Just did a rough test on the kitchen granite top and it seems to be very close.
 
Just remember, to calibrate you are not leveling anything. All you are doing is making sure the "Bubble" is in the same place at each end. To qualify the level give it to the pros.

"Billy G"
 
MattM said:
That is what I have. I will try this method.

Just did a rough test on the kitchen granite top and it seems to be very close.
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Levels are sensitive to position on your surface. Put some heavy object on the side and end so it is in the exact same place after you rotate it.
 
Here is how I ''calibrated'' my level. I had two goals, level my mill so I could align keyways in the ends of long shafts and get my level as close as I could to correct. The level was waaaayyyy off when I got it, very cheap though. Somebody who had no clue what they were doing had tried to adjust it and totally had it screwed up.

First I kind of leveled the mill with a 36 inch carpenter level so it was pretty close. Then I placed the precision level on the table (X axis) and made adjustments until the level was reading about the same error when rotated 180 degrees. This gave a pretty good starting point. Then I started adjusting the mill a bit, then check the level again and made small adjustments to the level as needed. Rotate 180 degrees check, rotate, adjust the level, adjust the mill, rinse/repeat. After about a half hour of this, the mill was level, and the level read the same in both directions. Then I tweaked the mill in the Y axis.
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mikey said:
I assume you're talking about a Starrett 98-18. If so, go here and download the powerpoint entitled "Calibrating and Maintaining Your Level" near the bottom of the page:

http://www.goodson.com/technical-library/

It pertains specifically to the Starrett 98 and is very clear.
Click to expand...
If it is a Starrett #98, it is not sufficiently sensitive to level a lathe, only their "master precision level" which is calibrated to .0005 p.f. has sufficient sensitivity for the task; I think the #98 is only sensitive to .005 p.f. Yes, I have both, and there is a huge difference between them, like a factor of ten.
 
benmychree said:
If it is a Starrett #98, it is not sufficiently sensitive to level a lathe, only their "master precision level" which is calibrated to .0005 p.f. has sufficient sensitivity for the task; I think the #98 is only sensitive to .005 p.f. Yes, I have both, and there is a huge difference between them, like a factor of ten.
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I would agree, at least in principle, but this is a can of worms. Lots of guys have used a Starrett 98 to level lathes and got it close enough to then use a test bar to do the final leveling. My Kinex level is twice as sensitive as a Starrett Master level and even then a test bar usually requires some very minor tweaking. One of my friends used a framing level and a test bar to level a 9X20 and, with some work, got that thing leveled dead on. That taught me something.
 
MattM said:
I scored a nice 18" Starrett level on CL yesterday ($50). It has adjusting screws. How do I know if it is in calibration? If not how do I calibrate it. Thanks.---Matt
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Check to be sure that the bubble vials are well seated in the level. If they are loose, that will have to be attended to first.
Then set the level on the flattest clean surface you own, usually a flat way of a machine tool. Make temporary marks at each end of where the level sits. On the long sides also, if you're on a wider surface. Note where the bubble reads. Then turn the level end for end (180 Degrees).

If the bubble reads the same, the level is in calibration. If not, tweak the adjusting screw until it reads the same facing both ways.
Note that the reading won't necessarily show that the surface is level. If at this point the level shows a certain amount off level for that particular spot on the surface, that's how far that surface is actually out of level.

If you've adjusted the level to read the same with it facing both directions (example 1/2 a bubble left, both ways), then the instrument is calibrated.
 
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