Position tolerance datums 3

[PtoMonty]

Hello all,

I have been trying to find an answer to this one and maybe you could give me your 2 cents. If I want to control the position of one hole in relation to another do you considered that I still need the 3 datums? Below I made a simplified drawing of what I consider to be a correct position tolerance for the hole in the top rigth. Am I till controlling all degrees of freedom? A is not in the picture but consider it as the plane defined by one of the faces perpendicular to the hole axis.

Thanks in advance.

 

[3DDave]

I am saying I see no indication you have enough control to avoid an interference fit with the mating part. Typically those users who don't know how datum references work also don't know how tolerance stackups work because one needs to understand datum references to understand tolerance stackups. Without analyzing the stack up it allows the chance for interference between the pins and the mating bushings.

As a suggestion, never put any numbers on an example when you just want a generalized solution.

The spacing variation allowed between the holes per what you put on the example is + and - .5mm on 9mm holes. That means the pins have to have at least that much clearance to guarantee a fit, plus whatever location tolerance the bushings have. That is looser than I would expect connectors to cope with.

Picking numbers like that makes it look careless, even when you are not.

As mentioned, you need to worry about the part of the pin that extends out of the part; this extension will increase the location variation that is part of the tolerance stackup. Not accounting for that also looks careless even when you are not.

 

[jassco]

Hi, PtoMonty:

So, you have a plate (let's call it "part A") with 6 holes two of which are dia. 9mm.

You will press two pins into those dia. 9mm holes.

What ("part B") will be attached to these two pins that stick out of the plate ("part A")? Is this "part B" a single part or multiple parts?

Best regards,

Alex

 

[PtoMonty]

Hi Alex,

Sorry but have been busy last week. It's a single part with two bushings. Bushing as slightly larger diameter to account for variation in position and diameter tolerances.