【转帖】olerance analysis to iso 8015 2768 part 1 9again10

yang686526

tolerance analysis to iso 8015 & 2768 part 1 (again!)
this is a follow on to
forgot to say, if someone knows of a reference that says the vendor is definitely wrong then that would be even more appreciated as it would mean i was right.
kenat, probably the least qualified checker you'll ever meet...
so i've either had a stroke of genius or i've been looking at this too long.
  kenat,
  
  what is the purpose of creating a dimension between the two holes? why can't each hole remain located wrt the datum they are called out to instead of to each other? while you are correct in that if one hole were located at one end of the tolerance and the other located at the other end, they would be .3 from nominal spacing but you can't leave one hole located wrt to a datum and then change the other to be located from the hole instead of the same datum and expect to be able to add a +/- .3 tolerance and achieve the same result.
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powerhound it's maybe a bad example but it's the one the vendor and engineer have been using.
i am not creating a dimension between the holesfff"> nor am i looking at re-dimensioning the vendors part in any way, i am looking at the mating part we make.
in the case of the holes i am just trying to understand how the hole position varies so i can put the appropriate clearance hole and positional tolerance on our mating part.  can i just convert the +-.15 to diameter and use standard positional calcs or does the fact that the gap between the holes is supposedly also +-.15 mean i use a smaller figure and if so what, +-.75?
if that example is so bad as to be confusion consider my second example on the radii.  they are essentially saying i'd calculate the nominal diameter by doubling the radius and then look up the table again for the tolerance on this calculated diameter.
to clarify what i stated in my second post about not being able to exactly match their tolerancing scheme.  their part is essentially square.  they use 2 edges as their 0 datum for ordinate dimensioning, effectively for the purpose of simple tolerance analysis i'm treating them as datums.  they essentially have a stepped female hole which our part sits in (the hole actually has a flat on one edge).
on our part i'm using one of the diameters that sits in their hole as the datum (with another datum on the straight chord for orientation).
kenat, probably the least qualified checker you'll ever meet...