Ra cast As-cast surface quality

How to verify

Comparison with tactile and visual cast surface comparator standards, which is the practical method and the one foundries use. If the drawing gives a roughness value, it is measured with a profilometer on a representative area and with a sampling length suited to a coarse texture; a single reading on a loose grain means nothing. Surface defects are assessed by size and density against the drawing criterion, using a magnifier and raking light.

Workshop guideline values

General

Ordinary sand surface, very rough, on the order of tens of microns Ra if it is measured at all.

Accuracy

Machine-molded or permanent-mold surface, clearly finer than hand sand molding.

High precision

Investment casting or die casting, which reach finishes comparable to rough machining without touching the part.

Guidance only: the drawing's value always wins.

Common mistakes when interpreting it

• Requiring a machining-grade roughness value from an as-cast face.
• Measuring cast texture with a profilometer as if it were a machined profile and relying on a single reading.
• Accepting or rejecting surface defects by personal judgment instead of against the limit set by the drawing.