Guide to Surface Plates with Recommendations for Smaller Sized Projects

May 22, 2020 4:29 pm

Surface plates are, quite literally, a machining fundament. They are exactly what they sound like: flat, solid plates (typically square or rectangular) that are used as the main reference point in precision inspection. The selection of your surface plate should be thought out since it will become an integral, structural element of the machine in which it’s mounted. Let’s look at a few key characteristics of surface plates along with some model recommendations.

Material

Surface plates come in a wide variety of materials, such as granite, cast iron, steel and glass. Most machinists prefer to use granite because of its inherent properties. Granite’s hardness, low thermal expansion, and no rust/corrosion quality make it the least likely to warp. There are two types of granite, pink and black, but there are fundamental differences between the two beyond just their color grade. Black granite is most commonly used and is best for applications that have significant load bearing requirements. Pink granite is not as strong as black granite but is incredibly resistant to wear. If your application requires frequent movement across the surface, pink granite your best bet. Keep in mind that the thicker the pink granite surface plate is, the heavier of loads it can bear.

Applications

Surface plates are usually associated with coordinate measuring machines (CMMs), precision optical assembly, or high precision industrial machines.

Surface plates are great for marking out, or transferring a design or pattern to a work-piece. Additionally, they are great for baseline work-piece measurements in machining and gage work.

Accuracy and calibration

The accuracy of a surface plate boils down to its flatness. Due to high frequency use, warping, chipping, and wear cause unevenness in areas of the surface plate. Even swarf causes damage to the plate, which is one of the many reasons why removing debris is imperative. A localized area of wear is common, due to the constant use of a particular tool, like a height gage, in the same spot.

Calibration and reworking of the surface place is normal and will happen regularly. However, before diving into calibrating your surface plate, you have to determine if it’s out of tolerance.

Here’s a great video to help you determine if your surface plate is out of tolerance, thus in need of calibration.

Cost

Surface plates can be wildly expensive, some are even thousands of dollars. The price comes down to not only the material, but also the size of the surface plate. The bigger the surface plate, the more it will cost.

Recommended Surface Plates

Here is a selection of five well-reviewed and affordable surface plates to consider for smaller applications.

Starrett Crystal Pink Granite Toolmakers Flat

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A portable and easy-to-move work-piece, this Starrett surface plate is best for layout work and gaging of smaller parts. Don’t forget the pink color of this granite will affect its properties, thus the function of this work-piece. Review our explanation above to make sure this tool suits your application needs.

Starrett Impala Black Granite Toolmakers Flat

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This has a similar build to the pink granite surface plate above so it is best used for smaller sized projects. Its portability makes this surface plate convenient for inspections throughout the plant. Again, note how the black color grade will affect this tool’s properties, as mentioned previously.

HHIP Granite Check with Fine Adjust

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This surface plate by HHIP is ideal for levelling small plane beds, has a fine adjustment attached and achieves 0.00005″ granite flatness.

HHIP Granite Surface Plate

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This surface plate comes with a certification of inspection, different size options and accuracy within ±0001″. An affordable option that does not sacrifice performance.

TTC Thick Grade Ledge Black Granite Surface Plate

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This surface plate is a great option for inspection work throughout the shop. Reviews have included nothing but high praise for its accuracy and precision.

 

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1 Comment

  • TG says:

    You skipped right over gray granite. Also, there is really no such thing as “Black” granite. Black surface plates are made from Gabbro, Which is stringer than granite, which is why they are usually thinner than their gray or pink counter parts.

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