All Surface Plates

[MIRCS]

All Surface Plate TO's

A-1: Surface Plate Calibration Using Electronic Height Gage (Use Only For TI's 12" or Smaller)

A-1.1 Set up TI as you would for any other method as determined by size. (i.e. draw lines and borders)

NOTE
For 12X12 use 1" borders.

A-1.2 Place the TI on top of the Leveling Plate.

A-1.3 Level the corners of the TI by using the electronic height gage.

A-1-4 When the TI corners are level to within 10µin, Start by moving every ½" on the first line and record the readings.

A-1.5 Start on the second line and record the readings. Repeat for all remaining lines.

A-1.6 Make a chart and store near the TI.

A-1.7 Annotate Certification Label with the grade the TI was calibrated to and the location of the calibration chart.

[howiesatwork]

It seems to me there is a shortcoming in this method.
The reference surface plate used as a base the whole setup is made on must be more accurate in flatness than the TI, as the base of the height gage must be moved over this surface to gage the TI surface.  
Any variations in the supporting reference plate will be telegraphed into the measured errors.

[MIRCS]

That is why the small plate is placed on a leveling plate and then leveled using the height gage. All error introduced by the bigger surface plate is then removed.

[howiesatwork]

That is why the small plate is placed on a leveling plate and then leveled using the height gage. All error introduced by the bigger surface plate is then removed.

It only makes the 4 spots that were measured at the corners a known distance to the reference plate.
Now, if the reference plate has a bow in the middle referenced to the end points where the stand for the indicator was when it was "levelled", an uknown error is introduced.
This is just one axis.  There are three more.
For this to work, your reference plate will need to be really flat, seeing that the specs for a 12X12 AA plate are tighter than that of the reference plate.
One more source of error:  Indicator stand base size and height and reach of the arm of the stand will multiply the error of the reference surface...
Why not do it with a Planekator?
You do not need to place the Planekator on the surface of the 12X12, but will need to raise the bases off the reference surface, spanning over the smaller plate, so you can measure with an indicator.  I don't have a picture of it, but it does work.

Autocollimator or laser is the easiest way to do all this anyway...

Howie

[MIRCS]

No kidding that an autocollimator or laser is the easiest way. The three footed leveling plate that the 12x12 is sitting on will take the larger plate out of the equation.

[howiesatwork]

Where is the base of the Electronic Height Gage sitting?
On the 12X12?