ANSI Y14.5M-1982 §1.6.2.b: "A dimension is expressed to the same number of
decimal places as it's tolerance. Zeros are added to the right of the
decimal point as necessary." It refers to ANSI B87.1 earlier in the
section, but I don't have that one.
ANSI Y14.5M-1982 §2.1.1 describes expression of tolerance, there is no
standard tolerance specified, all tolerances must be expressed as limits,
geometric, notes, referenced standards, or a general tolerance block.
There IS no default tolerance in Y14.5, but usual practice seems to be ±.005
for three decimal places on drawings I have seen and done. That tolerance
has always been specified in the title block or a tolerance block.
Sorry, this is the latest version of Y14.5 I have, maybe it changed when
ASME took it over? I also haven't specifically looked it up in IPC
documentation.
--
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272 Fax: 503-627-5587
http://www.tektronix.com <http://www.tektronix.com>
http://www.pcb-designer.com
It's my opinion, not Tektronix'
-----Original Message-----
From: Denis Lefebvre [mailto:[log in to unmask]]
Sent: Thursday, June 05, 2003 8:00 AM
To: [log in to unmask]
Subject: Re: [DC] IPC PCB Dimensioning standard
IPC does an extensive treatment of dimensioning and tolerancing but I do not
think you will find what a "three place" tolerance standard is within their
documents. Perhaps you need to look into ASME-Y14.5M.
It has been my experience, when dimensioning in inches, that X.XXX is +/-
0.005.
Denis Lefebvre, C.I.D.+
Senior PCB Designer
Finisar Corporation <http://www.finisar.com>
-----Original Message-----
From: Barry Gallegos [mailto:[log in to unmask]]
Sent: Thursday, June 05, 2003 7:35 AM
To: [log in to unmask]
Subject: [DC] IPC PCB Dimensioning standard
Good morning,
My Name is Barry and I have been asked to locate some information. As I have
had great
experiences with TechNet, I thought I would Give the Designer Council a Try.
So here goes.
I ask for some input on the following Message that I received this morning.
We have an issue on a customer drawing, where the customer calls out
dimensioning on their data, to 3 decimal places, but do not provide a
tolerance table or tolerance indication at all. The exact method the
customer used to call-out dimensions on their drawing is: 250Mils or 530Mils
for example. The pcb shop that built these is saying that, in the absence of
having a tolerance call-out, they default to IPC standard tolerance. The
customer service person at the pcb shop, cannot tell me which standard he is
referring to, nor can he tell me what that default IPC standard tolerance
might be. We do not have the 2221 IPC design standard nor do I know if it
would cover this issue. We have issue with the dimensions of these pcbs we
received, including hole positions.
Can you find out what the IPC default tolerance is for dimensioning of pcbs,
in the absence of having a specific tolerance call-out?
Barry Gallegos
Western Electronics
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