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Re: Lathe question forwarded

Subject: Re: Lathe question forwarded
Date: Tue, 26 Sep 2000 13:12:17 EDT
In a message dated 9/26/00 10:35:09 AM Central Daylight Time, writes:

> 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 
bubble location.  
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.

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.

Alex H.
Tulsa, OK

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