Surface Plate Grades and it's types

Surface metrology plays a crucial role in defining the properties of a surface, with surface roughness being a key parameter. It is essential for surfaces within manufacturing industries to adhere to specific roughness limits.

Click here for additional insights.

Watch Our Surface Plate Video

Subscribe

Thus, monitoring surface roughness is integral for quality assurance in the machining of workpieces.

Through effective surface measurement, we can forecast component performance and oversee the manufacturing workflow.

Essential Concepts in Surface Measurement

Flatness

Flatness refers to the vertical distance between the highest and lowest points on a surface plate.

Rigidity

Rigidity is the capacity of a solid object to resist any form of deformation.

Leveling

Leveling involves adjusting the table using its supporting mechanism.

Surface Plate Grades

Categories of Surface Plates

Surface plates can be categorized based on their material composition, classified into three main types:

1. Granite Surface Plates (IS, ISO -2)
2. Cast Iron Surface Plates (IS, ISO -1)
3. Glass Surface Plates (IS)

Granite Surface Plates

Granite plates offer enhanced rigidity without the risk of corrosion. They boast a high modulus of elasticity and remain unaffected by moisture.

Metal objects can easily slide on them, with common dimensions ranging from 400 x 250 x 50 mm to 250 mm.

Grading System

Grade-00 (Ideal for Metrology Labs)
Grade-0 (Recommended for General Quality Control Tasks)
Grade-1 (Suitable for Tool Rooms)
Grade-2 (Commonly used in Shop Floors)
Grade-3 (Utilized in Shop Floors, based on customer requirements)

Cast Iron Surface Plates

Cast iron surfaces are utilized following rough machining, requiring a suitable seasoning period and subsequent heat treatment to alleviate internal stress.

The accuracy for cast iron surface plates ranges from +/- 0.002 mm to +/- 0.005 mm for a diagonal length of 150 mm.

Available grades include:

Hengfeng

Grade-1 (Maximum flatness of 5 microns for a 300 mm x 300 mm plate)
Grade-2 (Maximum flatness of 20 microns for a 300 mm x 300 mm plate)

Glass Surface Plates

Commercially available glass surface plates are lightweight and devoid of burrs or corrosion issues.

Accuracy for glass plates ranges from 0.004 mm to 0.008 mm, with sizes between 150 mm x 150 mm and 600 mm x 800 mm.

Assessing Surface Roughness

Various techniques can be employed to inspect and assess the surface roughness of machined components.

1. Pocket Surf
2. Electronic Level

Learn more about this in our upcoming blog posts.

Stay Updated, Subscribe to Our Blog

We Hope You Enjoyed This:

Like

Loading...

Granite plates receive various grades: B for standard shop applications, A for inspection and tool rooms, and AA for laboratory use and machines such as CMM.

Typically, the grade/flatness of a surface plate is determined based on the flatness deviation per inch, along with repeatability over several inches. The size of the plate directly influences the complexity of maintaining its flatness.

Grade B Toolroom - 100 millionths
Grade A Inspection - 50 millionths
Grade AA Laboratory - 25 millionths

As defined by Starrett: "The tolerances for flatness across three standard grades are calculated using the formula:"

Laboratory Grade AA = (40 + diagonal squared/25) x . (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4.

A helpful rule of thumb suggests that the resolution of your inspection device should be ten times that of the item being inspected, which will guide your selection of a corresponding surface plate.

Grade B is more than sufficient for home workshop applications. However, if you can find an A or AA grade, that would benefit you significantly. For those requiring the precision of A or AA, engaging a company for lapping would be essential. Grade AA plates should reside in a climate-controlled environment with precise instruments to maintain their tolerances.

Starrett's pink granite is highly regarded, as is the feedback on Standridge plates.

You can frequently find these plates at machine shop auctions, often under $100.

They are invaluable tools—my own was acquired for free, previously part of a large CMM or inspection apparatus, measuring approximately 3' x 5'.

Contact us for your Surface Plates requirements. Our knowledgeable sales team can assist in finding the right options tailored to your needs.