Perpendicularity vs. Title Block Angle Tolerance 2

[Jieve]

Hello,

As I’m continuing to work on drawings for some simple parts and learning GD&T at the same time, I have some more questions for you helpful folks out there.

1)In one application, a short cylindrical spacer sits up against a shaft shoulder. There is a clearance fit 20 E8/g6 at the inner diameter of the spacer to the shaft. I have specified a total axial runout tolerance on the shaft shoulder of 0.1mm. There is a flatness and perpendicularity tolerance respectively of 0.1mm on both faces of the spacer. I have made a 2D drawing of the situation assuming max runout, shaft MMC and spacer MMC to make sure the clearance is still ok. I initially spec’d a perpendicularity tolerance for the hole and tried to work that into the drawing, until I realized that at MMC the parts must have perfect form and that a perpendicularity tolerance on the center hole is therefore unnecessary if the parts fit at MMC (if it is only necessary that they fit). However, I just read that at MMC edge perpendicularity is controlled by the title block angle tolerances (in my case the spacer is 5mm thick, so this means +-1 degree by ISO 2768-m). For a cylindrical part, does this angle refer to the axis angular tolerance to the faces, or to ANY line segment at any point (when rotating the part around its axis) where a face meets the hole? In other words, could the inner hole taper due to the fact that at 180 degrees apart from each other both angles of the line segments are 89 degrees? Or can only the AXIS itself be off by +-1 degree if not specifying a perpendicularity control? Btw. the outer diameter of the spacer has a total runout tolerance of 0.1mm, if this is important to the question.

2)Can anyone point me to a table somewhere with reasonably attainable tolerances within normal shop parameters for different geometric controls? I’m working from the ISO 1101 standard which has a table for fine, medium, course and very course guidelines for straightness, flatness, perpendicularity, symmetry and runout, just to keep my design in check, but something with a little more detail might be helpful including different machining processes. I found something like this once, but can’t find it again. I know machinery’s handbook has a table for IT tolerances resulting from different machining processes, but not sure it had something like this for GD&T (don’t have it with me now).

Thanks!

 

[fsincox]

pmarc & CH,
At this time I was taking simple fit to be: "get the pin in the hole, I don't care about how it sits on the bottom", was that what you mean here, too?

pmarc,
I mean straightness in the "common, whatever straigntness is there" sence. I don't really believe in perfect parts, just like I don't believe in line to line fits, CH
Frank

 

[CheckerHater]

I am not trying to “win” the argument here. This is all semantics.
If “hockey puck” in question actually has to rest on the bottom of the hole, then yes, indeed, perpendicularity affects the fit.
We both completely agree on the issue, we just cannot agree on the words to describe it.
It looks like you are more aggressively saying “perpendicularity will not affect simple fit”, and I am being more cautious saying “if simple fit is all you need, you better not specify perpendicularity”.
No hard feelings?

 

[pmarc]

Frank,
Yes, for the simpliest possible case of pin/hole fit and with no Rule #1 on the print, straightness tolerance is needed. My apologies for not giving you specific answer right away.

 

[fsincox]

pmarc,
No apologies are needed at all, I am just trying to understand the ISO comment as I myself have been thinking alot about the kind of implications of no rule #1. I agree, my understanding is, a perpendicularity tolerance will control straightness under ISO, though.
Frank