Mil-Std-100 3

[rgioff]

Anyone here very familiar with MIL-STD-100? I would like to know what it states about if drawing dimensions apply before or after finish plating.

any help is appreciated.

 

[btrueblood]

You do realize that MIL-STD-100 has been superseded by the ANSI Y14.100 series, since 2001?

That said, and just double checked in the rev. G standard, MIL-STD-100 does not really talk about plating, nor does it reference a plating spec. Even most plating spec's don't specify a "default"; some fastener spec's. mention it but don't define a default, for that question.

But, if your drawing calls for a plated part, and shows dimensions, I would ASSume (note the highlighted letters) that the dimensions apply for the finished, i.e. plated, part.

 

[rgioff]

Thats good to know! Im working with a very very old drawing. It called for the part to be cad plated but the question has come up if the machined dimensions are before or after plating. the customer asked us to follow the spec and could not give any other info. so the new spec doesnt say anything about this at all?

 

[btrueblood]

Is the plating called out on the drawing as a requirement? If so, then I would say the default for the part is that all of the stated conditions on the face of the drawing must apply, i.e. the dimensions are shown for the deliverable (plated) condition at standard room temperature/humidity conditions. You might dig into ANSI Y14.5 for the above "default", the 14.5 standard is part of the original -100 reference list, and is also referenced in the newer ANSI Y14.100 std. Wups, I keep saying ANSI when it's ASTM now, guess you can tell I've been around awhile.

 

[btrueblood]

Ok, looking at an old (1982) copy of ANSI Y14.5M (it was still an ANSI std. back then so nyah), which would have been in sway during the days of MIL-STD-100, in Section 1.4 "Fundamental Rules", 1.4.c states:

"Each necessary dimension of an end product shall be shown."

further, 1.4.f states:

"It is permissible to identify as nonmandatory certain processing dimensions that provide for finish allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing. Nonmandatory processing dimensions shall be identified by an appropriate note, such as NONMANDATORY (MFG DATA)."

So, again, the default is that the dimensions apply after plating, unless otherwise specified (but you still have to show the final dimensions). Pretty sure the above language holds in the latest Y14.5 as well.

 

[WKTaylor]

Adding to BTB's comments... alternate perspective...

I work with fairly old drawing [1950s]... the corporate standard... which helped evolve MIL-STD-100... has always been...

Dimensions 'before plating' and dimensions 'after plating/grinding' are mandatory for critical fits [must be on drawings]. Otherwise the machined dimension is as shown... and plating/coating finish thickness is additive [but controlled by finish specification].

Another perspective...

Generally speaking dimensions controlled to [4] decimal points mandate plating/coating thickness control. This is especially true for mechanical 'hole-to-shaft' fits, cam-surfaces, precision mechanical parts [close-tolerance fasteners], etc.

Generally, for [3] and fewer decimal places, plating/coating thickness control is pretty-much irrelevant.

NOTE. IF dimensions between a bolt and a '3-decimal point hole are somewhat critical', then generally the hole would have a special Flag Note regarding 'what to do', IE: 'no finish' [= mask-off]; or 'plating ONLY, omit primer], etc...

Regards, Wil Taylor

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[rgioff]

You are the man! thank you for the detailed answer.

 

[rb1957]

wot, no LPS ?

another day in paradise, or is paradise one day closer ?