Precision Level Accuracy Verification Process

The most important first task when performing machine tool precision leveling is to perform an accuracy and repeatability check on your precision “Spirit Level”. The procedure is very simple, you rotate the level several times 180 degrees and adjust so that you get the same reading at 0 and 180. Every level we have worked with has some means to adjust the level vial, you will need to understand your particular level to be able to perform the adjustment. An already known “Level” surface on one of your machines makes the calibration process easier but not necessary. In the below example we are using a surface that is not level to help explain the process. It may take several rotations of the level and more adjustment. Your goal is to get repeatable readings at 0 rotated 180.

Precision leveling of a Machine Tool requires the most accurate level available for the job. Levels come in all ranges of accuracy; Carpenter, Machinist, Precision and Ultra Precision, typically rated by an increment per distance; the most common being .0005” / 12” the most accurate “spirit level” we have found is rated at .0001” / 10”. Therefore, if you read between the lines, you can say 50 or even 25 millionths of an inch! (.000050” / .000025”)

Detailed level calibration procedure:

1.Make sure your level has been “normalized” to the ambient conditions.

A. This helps with the repeatability

2. Handling of the level should be kept to a minimum; thermal growth is your enemy.


3. Clean and “Stone” the surface you are using to get the most accurate and repeatable results.

4. Place the level and let it settle out.

A. Mark this spot so you can place the level back in the same location for repeatability.

B. Depending on the ambient environmental conditions and accuracy of the level this might take several minutes.

C. Make a note of the readings – remember them or write it down.

5. First Reading at 0 degrees.

6. Second reading at 180 degrees = 4 lines out

7. Adjust the level at 180 degrees removing ½ the error making it 2 lines out

8. Third reading rotate the level back to 0 Degrees to verify the adjustment.

A. Additional rotations and adjustments might be required.

9. Finally rotate it again to verify your final reading of 2 lines out.

10. Now you know that the level is precisely calibrated.

11. Adjust your machine to read bubble centered or more commonly known as 0 – 0

12. Index the level and you will see the same reading 0 – 0

Now you are sure your adjustments to the machine will deliver the desired results.

A precisely leveled Machine Tool

In the above example if you did not perform this check, you would have leveled the machine with a false sense of accuracy and your final results could be out of “Level” at least four lines.