Hole Tolerance Question

[JSNYDERCMC]

Hello,

I am trying to perform a tolerance stack up on a small assy. I have:

Block w/ Hole ID - 0.309 +/- 0.002
Bushing OD - 0.307 +/- 0.005
Bushing ID - 0.250 +/- 0.005
Pin OD - 0.244 +/- 0.002

I want to put the bushing into the hole and put the pin into that. I have never done a tolerance stack up on anything except examples (none of which I had anything like this).

Right now, my idea is to cut it in half and just do half of the stack up so it represents a more simple stack up.

Could someone give me direction on how to do this?

Thanks,
J

 

[KENAT]

Sorry, what are you trying to analyze?

Worst case fit of the bushing into the block is minimum block hole dia - maximum bushing OD. So .307-.312 so .005 interference - which may be a bit aggressive depending on factors you don't list.

Likewise Min bushing ID -max pin OD. So .245-.246 = .001 interference which again I don't know if that's appropriate for your application or not.

If you want to find max slop then do the opposite calculation.

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(probably not aimed specifically at you)
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[pmarc]

What kind of fit are you interested in? Clearance fit, press fit, transition fit?
Right now it seems that all fits are transition. You just need to compare:

#1:
a) min. ID of hole with max. OD of bushing;
b) max. ID of hole with min. OD of bushing;

#2:
a) min. ID of bushung with max. OD of pin;
b) max. ID of bushing with min. OD of pin;

In both cases there will be an interference in a)'s and a loose in b)'s, so this is typical transition fit.

 

[JSNYDERCMC]

Hey,

My question was not using worst case, I figured that out. I was wondering if I was using the RSS, more specifically if it was okay to take off from the outside to the center and then just double everything to get the entire hole tol.

Thanks,
J

 

[powerhound]

Right off the bat I can see that the bushing can be anything from a .005 press fit to a .005 clearance fit. It seems that a design should require one or the other, but not either one. This makes a difference in how the rest of the stuff stacks up. Can you re-evaluate and let me know if that was your intent?

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[pmarc]

And what does it have to do with RSS?

 

[JSNYDERCMC]

To clarify - The bushing design was just changed. We are switching to a plastic bushing with a slit in it, so it can fit a range holes, it has a .035" slit in the side and now has a .315" OD with and ID of .258 +/-.005 on both OD and ID.

With that said, it will fit down to a .305 hole if my math is correct, before that gap closes. Thus making it a slip fit all the time.

My asking for the RSS tolerance stack up is mearly because I am not sure if my method of doing this (in this scenario) is correct and I wanted to see if someone could tell me if my method works.

WC right now, I believe will have a .006" press fit. I would rather it be slip fit because we are putting a rivet (the pin) through the center and right now I am not sure how much that will expand.