A granite surface plate is a fundamental reference used in metrology for measuring parts accurately and for marking out of parts prior to precision machining.

This Granite Surface plate is Grade AA, this is the highest grade of surface plate, it is flat to within 1 micron, (Or Half-anantstesticle in Imperial units).

This is over spec for our needs! Grade B would normally be used on the shop floor - Grade AA is for Laboratory use for calibration of test equipment.

It is HEAVY, 30kg, and not attached to the small crate it's standing on, hence the warning above, please be careful when lifting or moving the plate. Ask someone to help, this plate is a 2 person lift.

Scratching the surface will ruin it so it is not to be used for lapping, cutting, bashing, or as a general purpose bench surface. Look after our tools, and they will look after us.

Please keep the plate clean and dust free.

This plate is accurate to 0.001mm or 1 micron. Dust in the air is up to about 500microns (0.500mm), Humans cannot see dust smaller than about 50 microns (0.050mm). If you touch the plate top, you will leave grease thicker than 0.001mm.

So if any dirt or dust to get on the surface, it can scratch the plate and ruin it, and it will mess up your measurements too. So:

• Wipe with a clean dry lint free cloth every time it is used, before using it and before placing anything on it.
• Make sure any metal surfaces are smooth before placing them on the surface plate, check by feeling the surface with your finger or the back of your hand, smooth with fine emery if necessary.
• Place items on the plate carefully to avoid chipping or scratching the plate.
• It can be used with engineers micrometer or bearing blue ( not the blue used for marking out surfaces ).
• Always keep the plate covered when not in use.

• Wipe the plate clean when you are finished.
• Clean off engineers blue with Isopropyl alcohol and let the plate dry.
• Replace it back in the box - Always keep the plate put away in the box when not in use.

There is Imperial Dial Test indicator and DTI stand with the Metal lathe, and vernier calipers in the metal lathe accessories drawers. Otherwise, the Hackspace does not have much by the way of metrology kit you will need to bring your own to use with the plate.

Do not attempt to polish out or otherwise remove scratches. Granite plates do not form a raised burr like metal plates and any attempt at repair will ruin the local flatness.

Machine Tool Reconditioning and Applications of Hand Scraping by Edward F Connelly

Explanatory A4 Label for the top cover of the surface plate

Side warning label for the surface plate cover