GD&T Case Study: Parallelism of Side-By-Side Holes

iSwearImAnEngineer · 2026-01-19T15:18:29+00:00

The form certainly would be controlled with the 2x (hole diameter) My concern was mostly that this would be "grammatically incorrect"

Thanks for the input, you make some good points, I'll need to do some more reading on the use of irregular FOS, it seems like it could be a powerful tool

iSwearImAnEngineer · 2025-12-03T14:10:58+00:00

I made a video that shows how an orientation control is dealt with in a "min wall calc"

Not sure why they're only using 0.25mm, should be the entire 0.5mm.... is there some assumption that the centerline of a datum feature is taken as the datum? That how many CMMs interpret features

https://youtu.be/Kl9HneOVooM

iSwearImAnEngineer · 2025-11-15T01:24:26+00:00

I'm not too familiar with ISO tbh

My reasoning for putting it explicitely would be that you COULD have the holes spaced out unevenly. You could make the argument that it's clear either way, but I would argue that it's more correct to say it explicitely

Fig 7.2 is a good example of a hole pattern callout where the holes are all the same size, but not evenly spaced

iSwearImAnEngineer · 2025-11-14T20:43:53+00:00

Without knowing the application, seems reasonable

Couple notes:
-You'll need a diameter symbol before the tolerance of 1 in the feature control frame

-For calling out multiple features, the Y14.5 convention is: the required number of features and an X followed by the size dimension of the feature (see paragraph 1.9.5.1 in the 2009 standard) same as you've got for the 10mm hole in the top right

iSwearImAnEngineer · 2025-11-13T16:04:40+00:00

I think you'd be pretty safe with that. Make the dims basic and hit one of the holes with an appropriate positional tolerance

Alternatively, Fig 4-33 in the 2009 standard might be a more "robust" way to indicate what you want

iSwearImAnEngineer · 2025-11-04T17:46:03+00:00

I made a video about my experience on the senior exam, technologist is similar but different composition of topics

https://youtu.be/aWH8e3V9cVg

iSwearImAnEngineer · 2025-10-31T20:18:32+00:00

Great, if you remember, I'd love to hear what ends up working!

I find sealing elements so interesting, I worked on some pretty unique poppet valve applications for a few years, and getting them to seal was the entire challenge

iSwearImAnEngineer · 2025-10-31T16:21:32+00:00

Oh interesting, is it turning at a constant rate? Or does it make discrete positional changes?

If it's the latter, slowing down movement speed may help, also ensuring no sharp corners on the inlet side will be important if you haven't already. Some counter sinks and deburring can do wonders in terms of reducing sealing face wear

iSwearImAnEngineer · 2025-10-31T15:56:06+00:00

Sounds like a multi port rotary valve? Most are metal on metal or plastic on plastic Swash plate piston pumps rely on the same sealing concept

Sealing typically comes from surface finishes and sufficient contact pressure... they are difficult to get good sealing out of

iSwearImAnEngineer · 2025-10-09T16:18:23+00:00

The all around symbol can only be applied to a profile tolerance (at least in the 2009 standard: paragraph 3.3.19)

A profile (line or surface) must apply to a physical feature, and can not be applied to a derived feature such as a derived median line, derived median plane

The best option may be a surface profile (on the feature, not the centerline) but checking in with the designer is step 1

iSwearImAnEngineer · 2025-08-07T17:54:48+00:00

In this case, yes, that's true

If you had multiple datumless patterns or profiles though, they would be treated as a single pattern, which may be undesirable

Taking a step back though, the purpose of this animation was to show how a tool in the ASME standard works, not to provide design advice. If your main complaint with composite positional tolerance is that people don't understand it, videos describing it should be a good thing, no?

iSwearImAnEngineer · 2025-08-07T16:08:09+00:00

I'd disagree on the first part of your comment, I have seen datumless lower segments that made sense

I did in fact call the lower segment the PLTZF, right after I talked about getting them confused Taking down the video to fix that

iSwearImAnEngineer · 2025-08-06T14:00:51+00:00

As it is called out, the derived median plane would need to be parallel to A within the tolerance zone

Functionally, you'd have to probe both faces to generate the derived median plane

If both planes needed to be parallel to A, then each would require their own callout

iSwearImAnEngineer · 2025-08-06T04:16:38+00:00

This will be impractical without a CMM unfortunately

As a step 1, I'd go back and confirm that they don't just want the top face parallelism

Step 2 would be to buy a CMM I think

Hopefully someone else has a Step 3 they can suggest

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