Surface Plate Grades and it's types

Surface Metrology specify the function of the surface. The important parameter is surface roughness.In manufacturing industries, a surface must be within certain limit of roughness.

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Therefore, measuring surface roughness is vital to quality control of machining a work-piece.

By Surface Measurement, we can predict the performance of the component and control the manufacturing process.  

Basic Terminology in Surface Measurement

Flatness

Flatness is define by the distance between peak and depth point of surface plate.

Rigidity

It is the property of a solid body to resist deformation.

Leveling

It is the process of Level the table by it&#;s support system.

Grade-00 surface plate

Types of Surface Plate

According to Material used, There are three types of Surface Plate

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

Granite Surface Plate

Granite surface plate have more rigidity for the same depth with the absence of corrosion. They provide a high modulus of rigidity and are moisture free.

Metallic objects like manufactured components/jobs can easily slide on their surface. The usual range available from 400*250*50 mm to **250 mm.

Grading System

Grade-00 (Prefer for Metrology laboratories ) Grade-0 (Prefer for General work in Quality Control)Grade-1 (Prefer for tool room)Grade-2 (Used for Shop Flore)Grade-3 (Also, used for shop Flore depend upon needs of customer )

Cast Iron Surface Plate

Cast-Iron surface plates used after rough machining is done followed by seasoning for suitable period. Then, heat treatment for relive the internal stress.

CI Surface table

The accuracy of this surface plate is +/- 0.002 mm to +/-0.005 mm for the surface plate diagonal of 150 mm.

CI surface plate available in 2 grades,

Link to Hengfeng

Grade-1 (Maximum flatness is 5 microns for 300mm*300 mm plate)

Grade-2 (Maximum flatness is 20 microns for 300mm*300 mm plate)

Glass Surface Plate

Glass surface plate commercially available. These are comparatively light in weight and free from burr and corrosion.

Accuracy varies in the range 0.004 to 0.008 mm. They are available in size of 150mmx150mm to 600mm*800mm.

Measurement of Surface roughness

Inspection and assessment of surface roughness of machined work-piece can be done by different measurement techniques.

1. Pocket Surf
2. Electronic Level

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Granite plates are graded, B for general shop use, A for inspection and toolroom, and AA for lab work and for machinery like a CMM.

Generally, Grade/Flatness is a function of flatness deviation per inch or several inches, and repeatablity per inch. The size of the plate is directly proportionate to the difficulty to lap in and maintain the grade.

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

From Starrett: "The flatness tolerances for three standard grades are defined in the federal specification as determined by the following 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.

If you follow the rule of thumb that your inspection device needs to be 10x the resolution of whatever you're inspecting needs to be, that will give you the range of what plate you want.

B is more than good enough for home shop use. If you can luck into an A or AA that's all the better. If you truly need the flatness of A or AA you'll want to have a company come in and lap it in. AA needs to be in a climate controlled room with very fussy instruments to keep its tolerance.

Starrett's pink granite is very nice, and I've heard great things about Standridge plates.

If you look at pretty much any machine shop auction, they are usually for sale and can be had for less than $100.

They are incredibly useful, I wouldn't be without mine. This one I got for free. Used to be part of a large CMM or some kind of inspection machine. Roughly 3' x 5' and ish pounds.

Granite surface plates are better for inspection and general use. Cast iron is preferred for lapping. Granite is more stable and wear resistant, which is nice for an inspection surface. Cast iron can be charged with lapping compound for making precision surfaces.Granite plates are graded, B for general shop use, A for inspection and toolroom, and AA for lab work and for machinery like a CMM.Generally, Grade/Flatness is a function of flatness deviation per inch or several inches, and repeatablity per inch. The size of the plate is directly proportionate to the difficulty to lap in and maintain the grade.Grade B Toolroom-100 millionthsGrade A Inspection-50 millionthsGrade AA Laboratory-25 millionthsFrom Starrett: "The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:"Laboratory Grade AA = (40 + diagonal squared/25) x ." (unilateral)Inspection Grade A = Laboratory Grade AA x 2Tool Room Grade B = Laboratory Grade AA x 4.If you follow the rule of thumb that your inspection device needs to be 10x the resolution of whatever you're inspecting needs to be, that will give you the range of what plate you want.B is more than good enough for home shop use. If you can luck into an A or AA that's all the better. If you truly need the flatness of A or AA you'll want to have a company come in and lap it in. AA needs to be in a climate controlled room with very fussy instruments to keep its tolerance.Starrett's pink granite is very nice, and I've heard great things about Standridge plates.If you look at pretty much any machine shop auction, they are usually for sale and can be had for less than $100.They are incredibly useful, I wouldn't be without mine. This one I got for free. Used to be part of a large CMM or some kind of inspection machine. Roughly 3' x 5' and ish pounds.

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