using 18-8 stainless material callout 3

[Tenkan]

I sometimes specify using 18-8 stainless as a material callout where an exact SS is not necessary and I want to give the vendor/machinist options for using material in stock, especially for small qty orders. I realize some of the 18-8's are not as preferred for machining but doable. My logic is if I'm ordering one or two parts why not give the most options for material when possible which the vendor might have in stock as remnants. I understand 18-8 generally applies to 301, 302, 303, 304... any stainless with at least 18% chromium and 8% nickel

This sometimes leads to confusion from vendors with a range of questions from 'which one' to 'can I use 303'...

My question is, is calling out 18-8 material for machined parts bad practice?

 

[btrueblood]

Just remember, UNS stands for Unicorn Numbering System.

 

[Tenkan]

I usually make the generic stainless callout read "any AISI/SAE type 3xx", or sometimes use "Any UNS S30xxx alloy steel".

bingo. I think this is what eluded my imagination in my quest for a correct way to specify a generic stainless callout. Sometimes my imagination gets stuck on a path but is actually tunnel vision...


I still have some curiosity about the 18-8 specification, if they can spec hardware out of it, then what is its standard? ...as mentioned prior, a standard does not exist? If its just simply defined as any 300 series that fits the 18-8 rule then technically it should not create confusion on a drawing!

a side note about price gouging on a generic material callout, any shop that would actually charge for the most expensive actual material remnant is not building a good customer relationship in my book. This may come down to semantics, but if I specify a generic material, I'm assuming the cheapest of the set quoted and used... or rather a small chunk of [reasonably] more expensive remnant is probably cheaper to use than ordering a blank new stock of cheaper grade, especially for a one off small part order. If they want to try me for some 3XX series unobtanium I'll find a new shop.

thanks everyone for the posts...

lightweight, cheap, strong... pick 2

 

[KENAT]

Yeah but then you have to qualify the new vendor, put the thumb screws on them to accept 90 day payment terms...

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[MintJulep]

All 300 series stainless is 18-8

Not all 18-8 stainless is 300 series.

I routinely reject the use of 18-8 hardware when 304 is specified.

 

[KENAT]

Well, I bought this up at my DFMA training today. Explained what we used to do, what purchasing told us to do and asked from a DFMA point of view what his view was.

Like most of my targeted questions he waffled a bit and was fairly non committal. He did come up with the obvious 'list more than one material' chest nut.

However, our manufacturing engineering manager did chime in quite strongly that the phone calls they'd get from vendors questioning what grad of SST/Al to use would out weigh any benefits.

I'd say more but I'm so underwhelmed by the whole training that I'm finding it hard to care.

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