Auditor has requested that the granite table in the lab be Calibrated

M

mark_B

hi - my auditor has requested that the granite table in the measurement lab is calibrated. The actual measurement device (laser scanner) is calibrated. I've never known this before is the request valid. any thoughts / suggestions would be welcome.
 
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bwayne

Registered
Re: calibration

Surface plate calibration is the only sure way to know you are working with a level surface. Surfaces will wear after extended usage and should be maintained in order to provide accurate measurement results. There are many accredited vendors out there that will come in to your facility to ensure your surfaces are flat and even.
 

AndyN

Moved On
hi - my auditor has requested that the granite table in the measurement lab is calibrated. The actual measurement device (laser scanner) is calibrated. I've never known this before is the request valid. any thoughts / suggestions would be welcome.

Hi and Welcome to the Cove!

Did your auditor "request" this action or write you a non-conformity?
 

Michael_M

Trusted Information Resource
What do you use the surface plate for?

Is the surface plate used when verifying conformity of at least one finished product?

The surface plate is typically treated as a measuring device if it is used as a means (or part of a means) to verify product conformity. We have an outside company come in once a year and resurface all the surface plates throughout the shop.
 

TWA - not the airline

Trusted Information Resource
If the laser scanner is the actual measuring device then you need to find out what this equipment requires regarding installation or from the MSA(what does the manual or the vendor say?).
 

JLyt207

Involved In Discussions
We also have to calibrate our granites. It is one more source of variation. They do change over time. We use our 4 a lot. They do get their share of use and abuse.
 

somashekar

Leader
Admin
hi - my auditor has requested that the granite table in the measurement lab is calibrated. The actual measurement device (laser scanner) is calibrated. I've never known this before is the request valid. any thoughts / suggestions would be welcome.
PRECISION GRANITE SURFACE PLATES
SPECIFICATIONS
FLATNESS TOLERANCE IN ?m FOR ACCURACY GRADE
SIZE OF
PLATE (in mm)
AS PER DIN 876:84
GRADE "00"
AS PER IS 7327-2003
GRADE "0"
GRADE "1"
GRADE "2"
GRADE "3"

Depends on the size and the grade. See the standard for details...

Also refer to (broken link removed)

FLATNESS TOLERANCE
The flatness deviation of a local area of 250 mm x 250 mm of the working surface shall not exceed :
1. 3.0 ?m for plates of Grade 00
2. 3.5 ?m for plates of Grade 0
3. 7.0 ?m for plates of Grade 1
4. 15.0 ?m for plates of Grade 2
5. 30.0 ?m for plates of Grade 3
 
S

Sean Kelley

A company I used to work for would have their granite tables verified and recalibrated as needed. The person that did this would apply various levels of abrasive material which would removed some of the top surface. The final step was a diamond power and he worked it around with a tool to make a very level surface. Depending on how bad it was and how accurate it needed to be he would work from 2-6 hours on a given table. Once done he would reseal the granite and perform final verification user a laser device. Sliding metal parts on the granite over time does change the flatness of it.
 
I calibrate ours, it is on a 5 year schedule, it all depends on how much it is used. We have several smaller ones that are calibrated more frequently (2-3 years), the big table is used only by me, so I can extend it some. If high accuracy measurements are not required, you can use a portable cmm to validate it for flatness, at least to a degree. Like other measuring equipment, there is no sense calibrating to ten digits if you only need two. Establish your need first then apply the necessary calibration.
 

AndyN

Moved On
But be careful! If the granite table is now a means to place a component upon, while measuring and datums are NOT taken from the plane of the table, the auditor is (pardon the pun) flat out incorrect! Some measurement systems don't rely on a flat plane to datum their measurement.
 
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