Desperate For help before my head turns purple

[UGMENTALCASE]

Morning All,

OK I've been going round in circles a bit and really need some help. I have 1 component, a bracket and a pin. The component is sat down, the bracket is set and doweled off to a base plate when in the correct setting position. The pin is then used to check two holes are in the correct place on the component, so passes through each hole in the bracket and into the component. Now firstly am I right in saying that this falls under floating fastener scenario?

So the hole in the part is 5.75 ± 0.15 positional tol at MMC is 0.4
I need to tolerance both the holes in my bracket and the pin to ensure they fit together.
The customer wants us to work at 10% of component tolerance for our parts. so our holes must be positional to 0.04 at MMC.

Can someone please help me out with the best way to start of calculating this out please?
I've checked numerous examples but they assume the positional tolerance between both parts is the same, and that's when I come unstuck

Please please help me!

 

[Belanger]

He's asking about datum shift, and whether it's directly additive to the total position tolerance (like bonus tolerance is). It's tricky because in a simple case like this where the datum and the feature toleranced from that single datum are acting in the same direction, then the "shift" tolerance can make the total available position tolerance appear to be more. (It's not that the position tolerance gets bigger, but it can shift around, thus making it seem bigger.)

But that doesn't happen in other situations where the datum acts in a different direction, or if the modifier is on a secondary or tertiary datum. Having an M or L modifier on that type of datum is too complex to explain here.

But greenimi, you rightly noted that that textbook is showing an ISO example! If we jump to the ASME rules, we could change the symbol from concentricity to position and then discuss the "shift" effect.

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

 

[pylfrm]

I am not very familiar with ISO either. That being said, if the features were manufactured to diameters 30.4 and 19.0, then based on figure 13.2 it seems you would have a "floating zone" of diameter 1.4.

- pylfrm

 

[UGMENTALCASE]

Morning,

Yes it's an ISO textbook, my other book is ASME, but this one has a good explanation of the MMC and LMC, the ASME book is a bit waffly. But as I was reading it I just wanted to ask that question.
Belanger I think is right, the view on the lower right shows the max positional tol (or 'floating zone') being 2mm DIA. So I was thinking well what affect does it have when the Diameter (Datum A) isn't produced at it's extremes like the view shows. So the view shows either it's smallest diameter and the biggest size diameters. So what happens in-between? Because one size relies on the other so to speak, so if the 30 diameter was produced at 30.4 what knock on affect does that have to the 19 diameter. So if datum A isn't manufactured to L, how does that affect the 19mm Diameter positional tolerance, of 'floating zone' as the book refers to it as.
So in other words, if it was produced at 30.4, what concentricity tol would this allow for the 19mm diameter?

Does that make sense? I feel I'm waffling now!