Typical tolerances for perpendicularity of press-fit dowel pins

[jvfeng]

Hello,

TL;DR: What's a common perpendicularity tolerance for a 3 mm h6 pin?

I have a common scenario where I have two steel dowel pins pressed into one part, which locate another part that has a hole & slot feature. Ultimately, I'm looking to see if anyone has any guidance on what sort of perpendicularity tolerance would be reasonable for these. The parts I'm working with used to be called out with plus/minus tolerancing, which only specified the position of the pin. So the perpendicularity has been basically whatever is best effort by the machinist. I also don't have precise enough equipment to measure the perpendicularity of the parts we have now.

Does anyone have a ballpark good value for perpendicularity of a press-fit pin? Say, a 3 or 5 mm diameter pin with an h6 ISO tolerance.

Many thanks!

 

[3DDave]

It seems like you are asking for process capability rather than what your design can tolerate. If you cannot measure the perpendicularity then both are a problem.

If the assembler is given a large enough mallet then the tolerance can be pretty large.

 

[jvfeng]

I'm also trying to get a little more generic than this specific component. What I'm looking for is a ballpark of typical values, something like what is shown in the picture below.

There isn't an exact threshold of will/won't work. It's a sliding scale of quality.

Source:

https://mae.ufl.edu/designlab/Lab Assignments/EML2322L-Tolerances.pdf

 

[Eric Gushiken]

Generally, for a small pin like that the perpendicularity would be less critical than for a large pin that sticks out more. You could just ignore a projected tolerance zone calculation or just add a small perpendicularity requirement like .001 but I just think it would be a pain to inspect on such a small pin. I would just leave it off unless it was super critical. Machines are usually set up to drill pretty damn perpendicular. My guess is you'd have tight positional tolerances so I don't think the machine shop would ever try to drill these holes by hand.

 

[MintJulep]

You are the designer of the parts.
You know (or should know) what variation your design can tolerate.
You get to choose the tolerance for all of the features that control how things fit together.

Notice how the words "tolerance" and "tolerate" share the same root.

 

[jvfeng]

Thank you Eric, ultimately this is really what I was looking for. The best solution for my problem is to use a position tolerance and use it as a datum, as described in the other thread linked below. You're correct in that the tolerance stack is primarily affected by the positioning tolerance, rather than the perpendicularity, for such a short pin.

https://www.eng-tips.com/viewthread.cfm?qid=421090

 

[jassco]

Hi, jvfeng:

Perpendicularity is not same thing as position tolerance. Rather, it is a refinement. Perpendicularity is related to depth of the hole that your pin is pressed into and to protrusion of your pin. Also, material type will play significant roles in perpendicularity. If you want a good perpendicularity, you will need to use reamer or sinker EDM.

I think there is a guide on Machinery Handbook. To control perpendicularity of the pin, you will have to control perpendicularity of the hole first.

Best regards,

Alex