How about changing to model based definitions?
In MBD, there are no explicit dimensions other than size tolerances. If one wants to interrogate the CAD model, one can get what the basic dimensions would have been.
Auto OEMs are going this route. Most don't even put basics on drawings...with...
Yes...I agree you only need 3-2-1.
But, is 3-3-3 illegal on a rigid part?
I was asked to explain based on interpretation of the standard.
I think it is illegal based on chapter 4...just like I think the 4 RFS pattern datum feature is illegal.
The reason...we can't draw a drf on a rigid part...
Let's say we have a rigid rectangular solid.
Someone put 3 well-spaced target points on the largest planar surface A1, A2, and A3...3 target points on the next largest plane B1,B2,and B3...and 3 target points on the tertiary surface...C1, C2, and C3.
If the first example is legal, this one is...
I had to fix the drawings because tier 1 suppliers like to get reimbursed for their tooling outlays. If parts receive production approval, then the supplier gets its $ investment reimbursed. If the parts never receive PPAP approval on enough programs, then the supplier eventually file...
As for the ordinate 0, the coordinate system of the part just needs to be related to the datum reference frame...it doesn't have to be identical to it.
John-Paul,
I think the 2009 change must have been made for parts that are not rigid. I have not read that chapter of the 2009 standard to the level where I could speak of that as anything but a guess though.
In terms of a rigid part though...with a requirement that at least 1 datum reference...
The ASME standard for dimensioning and tolerancing parts made from sheet metal is ASME Y14.5
This is the same standard as parts made by injection molding, or by 3D printing.
The ASME philosophy of tolerancing is based more on the function of the part than describing how the part is made or even...
For all you guys who think its always better to have an arbitrary B and an arbitrary C...
If you change a car tire, do you really tighten the "B and C lug nuts" first?
I don't know about a 70 hole pattern, but I've seen a 55 hole pattern on a Caterpillar large mining truck wheel rim.
There are several things to look at. If we are analyzing the wheel rim spinning around at high speeds after its attached to the knuckle, the the datum feature should be the...
ASME drawings tend to avoid describing bend angles...or other descriptions of how parts are made. ASME philosophy is to only describe the legal dimensioning of
the part after its made.
ISO...well...each drawing is more of a communication of the engineer's idea...rather than a legal document.
13 yes ago, the dimensional engineers of a placement firm convinced the company I was working at to go to LMC gaging. It was the interior systems integration program for a GM van.
LMC gaging was a colossal waste of time...at a time when the tier 1 supplier was trying to survive.
Eventually, all...
Greenimi,
There are quite a few topics that are not handled well in the standard.
This is one.
Perhaps this kind of confusion would be eliminated if a mathematics person were on the board.
I'll try to explain.
When there is a single hole as a datum fox @ RFS, the intent is for the mating...
Greenimi,
4.2.2
...Therefore, it is necessary to establish a method of simulating the theoretical reference plane from the actual features of the part.
I guess we'll have to agree to disagree.
Best regards,
Michael Liu
ASME GDTP S-0470
Greenimi,
The illegality is based on a violation in Chapter 4 Datum Referencing.
If one establishes 4 equal holes all toleranced @ RFS as per the example, there is no correct way to mathematically construct the datum reference frame's secondary datum plane...unless we allow theoretically perfect...
