How to Find Profile

[[Da...]]

Until recently, I have not seen many drawings with a profile callout. The ones that did have it were just one specific feature. 

Lately we have been getting a lot of new parts that have something like this as the only type of tolerance on the weldment or any of the components.

I barely understand what this means, let alone how to check it. 

I only have Calypso...no curve or freeform or anything like that.

All I can think is that I have to fully probe each individual surface and feature and make a profile dimension for each of them...but that isn't right either, is it? Because don't they have to all tie together somehow so it is the profile of the complete part?

Also, CMM inspections on welded parts are not done during production. So the people welding want to know +/- target and I was told to just spit it in half (so +/- .060 in this case) but I don't know if that is actually correct. 

 

[[DW...]]

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 You are correct, this note is becoming much more common on engineered drawings. Usually it is something like, "Unless otherwise specified all features must have a surface profile within XXX". This is the author's catch-all note to control 100% of the part geometry. Unless you are using a CT (X-ray) or scanner based system, you cannot reasonably perform this measurement. Where I work, we do have a CT based system, and when I actually do select ALL of the surfaces and evaluate the profile (usually to itself), the results tend to surprise the customer because for the first time ever someone is checking this note in its entirety. 

Edited yesterday at 03:19 PM

[[Da...]]

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Since you are online at the moment, can I ask you another question?

What does the composite tolerance mean? I am not very familiar with them either, and I am even more confused since there is no datum.

 

[[St...]]

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Hello Darci, for composite/Multiple Single Segment position, I recommend reviewing Faro.com's and GDandTbasics.com's material on this topic.

I haven't seen them without datums however, so I can't help with that. Sorry!

[[Ke...]]

https://www.gdandtbasics.com/composite-position-vs-multiple-single-segment-tolerances/

I'm pretty sure ASME requires at least 1 datum for position. For example, a cylinder with a position to the bottim surface plane would essentially be an evaluation of perpendicularity.

[[Ky...]]

For the profile, it would depend a bit on the part itself. You can do surface profiles (most) standard geometries, though there is a bit of a trick to it with the old GD&T engine (see https://portal.zeiss.com/knowledge-base?id=868503). Additionally, you can do it with individual points, but it is significantly harder (see https://portal.zeiss.com/knowledge-base?id=2495545).

[[Pa...]]

That position callout is, in fact, incomplete.  There's nothing you or Calypso can do to report a position relative to nothing.  This says you can put these holes in the wrong workpiece and still pass the PLTZF.  As long as your two holes are spaced properly you will also pass the FLTZF.

Your company will need to contact your customer.  The DRF needs to specify at least one datum to control orientation.  A composite position like this needs fewer datums called in the FLTZF (lower segment) than the PLTZF (upper segment).

Let's pretend the callout is complete.  I'll use a datum A plane as primary for both segments, a cylindrical bore in that face as datum B used only in the upper segment, and a plane C perpendicular to A for tertiary in only the upper segment.

Evaluating the upper segment, the tolerance zones for the two holes are (first) perpendicular to A and (second) equally spaced and centered around B, then (third) the entire pattern of tolerance zones 180° apart rotated around B based on their required relationship to C.  This tolerance zone will be the larger of the two (.030) per the standard (assuming ASME).

The lower segment with only datum A creates two smaller tolerance zones which are perpendicular to A.  There is no requirement for their placement relative to B, nor a rotational component to C.

In a composite tolerance BOTH must pass.  Here's a quick demonstration of how this might go:

1. Holes both were machined perfectly at their nominals.  Both PLTZF and FLTZF pass so composite position passes.

2. holes are equally spaced perfectly, but the pattern's rotation is "off" to C.  The PLTZF would fail but the FLTZF would pass.  Since one failed, the entire composite position fails.

3. holes are equally spaced around B and perfectly rotated to C, but they are both radially .007" too close to B.  Here you'd find the PLTZF passes while the FLTZF fails.  The composite position fails.

So the upper segment provides a large tolerance for location of the pattern on the workpiece, which is why 2 or more datums need to be called.  The lower segment is free to rotate and translate on the workpiece as long as their relationship one to the other is correct.  And at the end of the day both must pass.

Attached is a nice visual representation.  This may or may not be the presentation Steven mentions above.

True Position Bore Pattern.pps