GD & T Help needed please!

[UGMENTALCASE]

Good evening all,

I've been researching GD & T and purchased some good reference books which have helped me understand a lot, however I think I'm confusing myself a bit. In examples in the books I've been reading you have a pin and a hole. Hole is tolerance 12.0 + 0.1 - 0.1, so we calculate MMC and similarly with the shaft/pin. Calculate the VC and that's it, the parts fit together.
I'm struggling to find a real life scenario, so to speak. I've attached an image the blue outline is a profile, the grey inner track is a checking pin shape. Don't ask why it's just this shape (I have a similar situation I'm looking at) The line tolerance is stated, and there are some boxed dimensions. As far as I can see the only thing defining the line, is the profile tolerance, there are no ± dimensions anywhere etc. So if I were to want a fit of something like a g6 in this profile, could someone please help me out with how you would go about calculating it please?
I've gone over it as per basic examples (briefly outlined above) but I some how convince myself I'm doing it wrong, though I don't think I am! I've put an example of what I'm looking at on the end of the attachment. I hope this comes across ok, the example on the attachment is just a random tolerance to show how the hole and pin fit together, it's not using actual fits. I think I'm missing something somewhere but like I say I keep going round in circles!

Thanks in Advance

 

[drawoh]

UGMENTALCASE,

On your sketch, the profile tolerance completely controls your outline. The profile controls the size of your hole, and its position with respect to your datums. There is no need for a [±][ ]tolerance.

Read up on profile tolerances.

Your profile tolerance of 1mm imposes a width tolerance of [±]1mm. This is way too sloppy for a tolerance that mates with[ ]g6. The Machinery's Handbook shows H7. I would argue that you could apply a width of 16.018/16 to your slot. The profile would control the location of your slot. There was a discussion on mixing profiles with [±][ ]tolerances in thread1103-400077 in which I was disagreed with. You should read through it carefully.

--
JHG

 

[UGMENTALCASE]

Wow that's quite a thread! Well the slot/hole is set in stone. Let's say that's the component so I can't change that, the bit I just need my pin to fit in. And I suppose in a sense it leads to another questions, how do you tolerance the fit on something as sloppy as that? If the fit between them was better, I'm thinking of something like a 12 DIA hole H7 g6, the fit comes straight out of a book, and it will work. But if the tolerance is dictated by component drawings (in this instance) what do you aim for?

 

[drawoh]

UGMENTALCASE,

Given that your outline is controlled by the profile tolerance, your maximum clearance cannot be less than a millimeter. For one piece only, you can measure the slot, and fabricate a pin to fit. For a batch of interchangeable parts, you can make a 10mm pin and systematically pick up one side of the slot. This will not be accurate, but it will be repeatable.

--
JHG