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I Bought a New Granite Surface Plate

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I bought another new granite surface plate, with this one being 12″ x 18″ x 3″ and with 2 ledges.

It’s a Grade A plate with 0.0001″ surface accuracy and 0.000060″ repeat gage reading.

Generally, B is toolroom grade, A is inspection grade, and AA is laboratory grade. The higher the grade, the higher the accuracy – and price.

Granite surface plates provide a flat reference surface.

In total, I have a Starrett 12″ x 8″ x 2″ “toolmaker flat” for portable or office use (also a recent purchase), a new Precision Granite-branded 12″ x 18″ x 3″ surface plate (shown above), and an older B-grade surface plate that I bought 15 years ago from Enco for $15.

While I was hoping to buy a larger Starrett surface plate, they’ve been backordered at every supplier for many months. If I ordered one last spring, I likely still wouldn’t have one. I luckily managed to find another USA supplier.

I upgraded more of my metrology equipment as well, such as splurging on a digital height gauge to replace a much cheaper one with a dial readout. I bought the dial height gauge more than 10 years ago, and never liked using it.

I also bought a cylindrical square for use with the plates, and the cost was painful. I went with a USA-brand there too, and regret it a bit, as it’s hard to move around. Import squares come with handles.

There are measuring tasks where all of this comes in handy, but there are also some checks that can only be done with a flat reference surface.

Imported toolroom B-grade surface plates can be found for less than $100, and they’re still decent. My older one will continue to be used in other ways, such as a sandpaper lapping plate for polishing or sharpening tasks.

If you’re interested in more detailed posts about precision measurement tools and the like, please let me know!

In the meantime, I’m going to have to find a cover for the surface plate to protect it from dust and debris. Any ideas?