Note: Machine as a pair
Note: Machine as a pair
(OP)
I've come across this note several times before. My understanding is that they would like to hold a dimension to be identical such as a pair of rails for assembly. It there anything in the GD&T callouts that would do something along the lines of this note? I was thinking about using profile of a surface with a datum reference, but that would be a tighter tolerance if I want better match between the two parts. Any thoughts?





RE: Note: Machine as a pair
Perhaps I'm being too much of a stickler :)
Profile of a surface sometimes has a similiar connotation, such as with coplanar surfaces (compared with a flatness callout). And there is also the rule of simultaneous gaging. Other than those ideas, I'm not totally sure what you're trying to do.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Note: Machine as a pair
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Note: Machine as a pair
If the parts are machined from separate stock, the there is nothing in Y14.5 to relate the two separate parts. If they are parted from one machined piece, then you may be able to use <CF> (Continuous Feature) or Profile of a Surface to control the workpiece before parting. The drawing would have to show the multiple machined part joined with phantom lines to show the relationship. After parting, there is no relationship between the parts though, so the controls only apply pre-parting.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Note: Machine as a pair
We drew the 2 parts on one drawing as I recall. We gave information on which face they were to be mounted for 'inspection' and indicated which dimensions applied to the pair.
We kind of did it like you would a non rigid part.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Note: Machine as a pair
leeekim,
The “drafting standards” are not limited to Y14.5
What you are talking about is called MATCHED SET.
You may find description of this technique in ASME Y14.24
RE: Note: Machine as a pair
RE: Note: Machine as a pair
Thanks CH, some around here will not like a radius as a datum feature, I like it though.
We did a lot of this "matched part" kind of thing, too.
RE: Note: Machine as a pair
I feel like brandy
RE: Note: Machine as a pair
I (for one at least) have no problem with the radius being a datum feature. It's not a feature of size, but that's not a requirement; a mathematically defined surface makes an effective datum feature. Of course, +/- tolerances on the radii is bad, but that is not the point of the drawing.
tks for the reference, CH.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Note: Machine as a pair
Thank you for your reply, so we agree that due to ASME rules it is not a FOS. I am on board with that, now, as it is the "law" (for my land anyway). A radius as a datum is OK? But, using +/- tolerancing of the raduis is questionable? The tolerancing is hard because it forces you to find the center?? Doesn't its use as a datum do that also? Sorry, I have been having a hard time with this and have applications just like this part only not actually split, otherwise it is just like it, partial circular plate with a radial hole pattern emanating from the center point of the theoretical partial circle. Profile of the whole thing is frowned upon, although, I have made progress with it.
RE: Note: Machine as a pair
In the figure CH posted, what is the relationship between the radii segments? There are 4 of them that need to be related back to each other or to datums A/B/C. There is an IMPLIED coaxiality of the features, but no control provided. If they were FOSs, then position could be used. For better or for worse, the only geometric control that locates surfaces is Profile of a Surface. As the radial "size" dimension is based on a center point (i.e. center location), it must be repeatable to have any kind of functional meaning. By the Principle of Simultaneous Requirements, if the two outer radii (R9 & R11) were controlled with a profile of .02/A/B/C, and the two inner radii (R9.938 & R10.062) were controlled with a profile of .01/A/B/C, then they would all be gauged/inspected together, making the actual center irrelevant. That would, however, establish legitimate controls for the implied condition that I read into the drawing. The datum feature simulator for radius segment datum feature B, establishing Datum B, is of "perfect form & size" within gaugemaker tolerances, and therefore it can be used to establish a center that would be used to locate the four holes controlled with position.
From a Y14.5 perspective, this drawing is rather poor. Some controls are evidently missing, and the two surface profiles (2 SURFACES on each) should be wrt the DRF as well.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Note: Machine as a pair
Thank you, again. I also thank others that have tried to help me struggle with these concepts.
Frank
RE: Note: Machine as a pair
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com