In a message dated 9/26/00 10:35:09 AM Central Daylight Time,
> So how do you zero a machinists level?
This whole process is based on the principle that a perfectly calibrated
level will show an exactly centered bubble when placed on a perfectly flat,
level surface in any direction. You have probably been taught to reverse a
carpenter's level to see how far off it is. Same process here but the
Machinist's Level has built in adjustments so it can be corrected when it
gets off. Roughly the same process works on optical instruments such as
manual levels, transits, older theodolites, etc. I should note that I have
no formal schooling in this, just what I have seen others do and what has
worked well for me over forty years. YMMV Someone else may have an easier
way or more concise directions.
The vial has adjustment nuts on one or sometimes both ends of the vial.
There will be one nut on top of the vial mounting and one on the bottom of
the vial mounting. These nuts will have small holes drilled in them at
regular intervals. Find a small pin or drill bit butt end that fits the
holes. The vial is adjusted by loosening/tightening the proper nut to bring
the vial to parallel with the base of the level. We will assume you have a
perfectly flat, smooth surface to work on. Never touch the vial at any time
during use (uneven heat causes errors). The level should be at the
temperature of the shop for at least thirty mins. before using (store it
where you intend to use it)
Operation 1. Set the level down on the plate and carefully note the exact
Operation 2. Turn the level exactly 180 degrees and carefully note the exact
bubble location again.
NOTE: Do not attempt to adjust the level vial until you get to Condition D.
Condition A. If both the plate is level and the level is in calibration, the
bubble will be in the exact center of the vial in both positions. Level is
ready to use.
Condition B. If the bubble is off in the same direction (even if the amount
varies) in both positions, the plate is not level. Adjust the plate to level
in both directions and start over at Op 1. If the bubble is off the exact
same amount, only the plate is off. If the bubble is off by different
amounts, the level has some error also. Average out the difference as best
you can, start over at Op 1.
Condition C. If the bubble is off in opposite directions by different
amounts, both the plate and the level are off. Adjust the plate closer to
level as best you can and start over at Op 1.
Condition D. If the bubble is off in opposite directions by exactly the same
amount, the plate is level and the level is out of adjustment, go to
Operation 3. You should be here only if the level bubble is off exactly the
same amount in the opposite directions. Using the pin that fits the
adjusting nuts, loosen /tighten the appropriate nuts to take out a little
more than half the error. Go to Op 1. After a few repetitions, the bubble
should be exactly centered. Be very careful not to over tighten the nuts.
Tried to make this as clear as possible, hope I succeeded. After you do it
once, you will never forget it. Email me direct if you have any questions.