?Flatness Specs and Conversions?

[sprintcar]

What's the best way to specify flatness for machined pads (bolt down area) on a base? Some are shown in/in, some in/ft and there's a question regarding the best way to convert to Metric callout (mm/M?), including the right conversion formula (we've been shown 3 different ones...)

Is there an ISO, ASTM or SAE standard available?

All help would be appreciated!!

Thanks!

Racing and bullfighting are the only real sports...everything else is just a game.
Bob

 

[Capntom]

ANSI spec for geometric tolerancing. I believe it is 14.5. The callout could be flatness of a surface. I say "could" because of the fact that there are many ways to accomplish this. If you use all of the pads as "the surface". Remember that this surface is a datum plane in itself that others are referenced to, Perpindicularity or True Position etc..

 

[sprintcar]

Thanks - we've got GD&T ref on the dwgs but we're dealing with foreign inspectors who are looking for in/ft type references so they can measure the pad (rise and run) to get units they want

Racing and bullfighting are the only real sports...everything else is just a game.
Bob

 

[unclesyd]

If my recall is correct the way we called out the tolerance on bases was in/foot(.001) cumulative and the way we measured it was with a long enough straight edge to span the base in two directions and used a feeler gauge. This was before CMMs.

 

[PatRiordan]

There are several ways of specifying this according to ANSI y14.5. One of the favorites that I call the engineers garbage pail is profile. This can be specified either as a bilateral or unilateral zone and incorporates flatness, position and form.