Flatness measurement

[FrankSmith]

I am looking for a way to measure steel plates flatness. The plate is 3'X 5' and is approximately 2 inches thick. I believe that the plate is slightly concave on one side. Is there any instrument I can use to get an exact meamsurement? I have already used a a straight edge.

 

[CoryPad]

Coordinate Measuring Machine (CMM)?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

What kind of accuracy do you need?
A straight edge is usually close enough for most purposes. Right off you can check the standard under which the plate was ordered and see what is allowed dimension wise.
You can get very accurate measurements though it its usually less expensive to have the plate finished or purchased to the desired dimensions.

Come back with a little more information as to the results you are expecting.

 

[Barry1961]

You could use a optical level with a micrometer attachment. The level is similar to a transit and is used to level machine bases such as large lathe beds. Most are good to .001" at 100'. You should be able to rent one at a local surveyor shop for about $35 a day.
They work by first leveling the level then aiming at a white faced venier scale at different points on the plate. In your case I would probably do readings in a grid pattern then calculate the slope and surface contour.
These instruments are tricky to level the first few times but you should get plenty of practice after everyone and their brother kicks the tripod while trying to look thru it.

I am going to assume this plate is evenly supported.

Barry1961

 

[MintJulep]

Put the piece on a surface plate. Mount a dial indicator on an arm with a base on the surface plate. Move the indicator, or the piece.

 

[deanc]

Your plate should meet ASME SA-20/ASTM A-20 for flatness. Make sure you read the entire paragraphs and do the rounding(the mill does). For this a straight edge and a taper gauge should be enough. If the plate is shy on one side-UT it for thickness A-20 again.

You can order plate to half tolerence. A good plate roll man/person(PC) can make it flatter.

 

[JoeTank]

FrankSmith,
deanc is right. I could also imagine that the pyramid builders would do it exactly the same way. ASTM A6 has permissible plate waviness tolerance for structural grade plate. ASTM A20 has tolerances for pressure vessel grade steels.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[MintJulep]

Crap, 3 x 5 feet. I saw inches before.

 

[funnelguy]

Don't sweat it, Mint. I've checked bigger parts than that on granite surface plates. Either the surface plate/indicator or CMM will get the answers Frank needs if a straight edge and feelers aren't accurate enough.

Find a local Blanchard grinding job shop and have them sweep the part for you until you develop in-house inspection capabilities. (Assuming they check flatness...)

 

[dgallagher]

Any reputable laser alignment service group should be able to do this for you. If you wish to do in-house, here is equipment to do the job.

Application:

http://www.damalini.com/pages/en/flatness_eng.htm

Product:

http://www.reliabilitydirect.com/alignmentproducts/DAM-D525.htm

http://www.reliabilitydirect.com/alignmentproducts/DAM-D22.htm