hole pattern position callout with no datum referenced
hole pattern position callout with no datum referenced
(OP)
This is ISO based print. Imagine a cylinder, there are bolt holes on the flange of cylinder evenly spaced around the axis. Now the print specifies position tolerance for the hole pattern, see attached.
If the surface of flange is datum plane A, is the position callout in attached print same as 25 X |pos|ø0.3|A|?
If the surface of flange is datum plane A, is the position callout in attached print same as 25 X |pos|ø0.3|A|?





RE: hole pattern position callout with no datum referenced
Frank
RE: hole pattern position callout with no datum referenced
RE: hole pattern position callout with no datum referenced
The tolerance zones are perpendicular to nothing. But they are parallel to each other and distanced from each other at a fixed location.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: hole pattern position callout with no datum referenced
This practice is shown in ISO 1101:2004.
RE: hole pattern position callout with no datum referenced
RE: hole pattern position callout with no datum referenced
It may be done in 2009 by people who have not changed their thinking in 40 years, It is very common for engineering people to say "well it worked before".
That statement still says the same thing as it always did, the meaning has not changed. The standards have evolved and it is just not considered "good practice" anymore. There are not that many of us who even care about these things, unfortunately. You have three of them here.
Frank
RE: hole pattern position callout with no datum referenced
Frank
RE: hole pattern position callout with no datum referenced
I then got to thinking for all you guys who don't like putting perpendicularity on short secondary datum features, that might be a good solution for you too, don't make it a secondary datum, just make it primary, like they did in the GOOD OLD DAYS.
Frank
RE: hole pattern position callout with no datum referenced
RE: hole pattern position callout with no datum referenced
It is just a very thin (.100" thick) round part, I recommended the face to be the primary datum, they are making the OD the primary datum to simplify changes. It has multiple patterns of holes that reference a datum "A" but no datum on the drawing. I recommended changing to "A" (primary), "B" (secondary). It does sit on the face, and the holes are fastener clearance and the OD is just to "hold the holes in", by the way.
Frank
RE: hole pattern position callout with no datum referenced
I have seen drawings that have datum features specified, but no feature of the part references any of the datums. There are fom controls, but no position, orientation or other types of feature control frame on the drawing. How do you like that?
This should be another topic though.
RE: hole pattern position callout with no datum referenced
Right, I see both, too.
Good point.
Frank
RE: hole pattern position callout with no datum referenced
RE: hole pattern position callout with no datum referenced
Right, as far as I know this has always been true for ASME & ISO.
Frank