I got a question in from a student to this year's workshop with is media question.

His spec says to use SAE S230, S280 or S330 cast steel shot, however, they want to use CW-28 (Conditioned Stainless Steel Cut Wire) instead. Acceptance to do this isn't stated anywhere.

My official answer is that they must get approval from their customer in writing to do so.

The benefits from doing so are obvious. My question is, why wouldn't a company allow the swap?

I've asked the questioner to sign up to this forum to follow any answers.

The surface finish will be rougher than they are used to seeing. If this is not a problem, then there is no other reason not to permit it's use in my opinion.

So you are saying that if the size and mass between the two media types are the same, the rougher surface of the cut wire media vs the cast shot is visibly noticeable on the resulting peened surface?

Yes that is what I'm saying. The amount of the difference is proportional to the amount of conditioning pefromed on the cut wire. Obviously the more the better. However, the peened surface will never be as smooth as cast steel under optimal conditions.

The difference in dent smoothness will depend upon the degree of conditioning that had been applied to the cut wire shot. With a low level of conditioning then there will be a noticeable difference in peened surface appearance. "Special conditioned" cut wire would give a difference that would be difficult to detect.
A second concern would be the chemical composition of the components themselves. Stainless steel components, for example, would generally benefit from using stainless steel shot rather than carbon steel shot. Carbon steel components, on the other hand, could suffer greater corrosion if stainless steel fragments had become embedded on peening.

I hope he "tunes in" for this info. This is something I didn't know and why I'm pushing for people that contact us for questions directly to put them up hear instead.

I can count on people like you, Walter and some guy named Jack to be a great help!