orientation or form error considered in min wall thickness stack? 1

[bxbzq]

Hello,

I think this a simple and classic tolerance stack example. Please see the sketch to the left of the attached pdf. In the textbook I have, the answer of the min wall thickness x is 2.9mm. However, to my understanding, the calculation does not take perpendicularity or form errors into account when the two holes are at LMC. So I added the perpendicularity and form errors and did worst case calculations as shown to the right. Any comments on my understanding and calculations?

Thanks.

 

[pmarc]

Yes, this is true. But in this case the hole will occupy dia. 10.8 space equal to resultant condition of the hole, not dia. 10.4. That is why I said it would be a magic to meet all 3 conditions.

Is this what your post was refering to?

 

[CheckerHater]

And about rules for measuring thickness – makes all the difference in the world.
The entire purpose of GD&T is to ensure fit and interchangeability.
From fit and interchangeability point of view, which “thickness” do you think is more relevant?

 

[Belanger]

Guys -- remember that the original question was to find the minimum distance indicated as X.

That verbiage doesn't mesh with any particular GD&T terminology, so we need to either make an assumption or ask the questioner to be more specific.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[pmarc]

CH,

From fit and interchangeability point of view, that is to assure that both parts will always mate together if all tolerances are met, neither T1 nor T2 is relevant, or at least this is not the most important factor I would care about.

First of all I would focus on assuring that surfaces of holes and pins may never violate their inner (in case of holes) and outer (in case of pins) boundaries (most likely their virtual conditions, if the assembly is the only concern). On your picture it looks like full mate is impossible because diameters of the holes at the bottom are smaller than size of the pins.

 

[CheckerHater]

pmarc,

If you REALLY don't understand what I am trying to say, I will provide better picture on Monday.

Belanger,

Yes, this is my assumption: distance indicated as X represents amount of space critical for part to engage mating part / gage, so it's boundary-to-boundary, not worst point to worst point