Locating Hex-shaped Pin Holes

[randy64]

Plastic part. I have a pattern of 4 hex holes for round pins to go into. How do I locate the hex hole pattern? My first thought is to treat it kind of like a round hole pattern, but show dimension across the flat of one hole as follows:
4X .072 HEX
|LOC|DIA .005M|A|BM|

Upon doing some research, I seem to find the solution to be using profile of the hex shape, but I'm not sure how that helps to locate the hex.

Any and all help and/or examples is appreciated.

 

[CheckerHater]

One idea could be using irregular features of size.

You consider cylindrical envelopes created inside of hex holes and locate those envelopes as if they were cylindrical holes.

Functionally you place cylindrical pins into the holes anyway, so the (imaginary) checking fixture will have set of round pins to check hex holes as well, which is exactly what the idea of irregular FOS is.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[randy64]

CH, can you direct me to an example of what you're talking about?

Thanks

 

[CheckerHater]

I don't have a copy of the standard on me right now but I will try find something.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[randy64]

*Shocked to learn that CH does not constantly carry copy of Y14.5*

 

[ewh]

I carry one on my keychain.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[drawoh]

randy64,

Are these accurate holes on a substantially less accurate pattern?

--
JHG

 

[randy64]

They are hex holes for round pins that are pressed in to them, a pattern of 4. So, I'd say that the fit and location are both pretty accurate/critical. The interference on the fit is .003" across the diameter/flat, and we're looking at locating them to about as tight as the molder can hold them (maybe .003"?).

 

[SeasonLee]

but I'm not sure how that helps to locate the hex.

Any and all help and/or examples is appreciated.

The top FCF controls the size, location, orientation and form.

http://www.dimcax.com/gdt_web/september-00.htm

 

[randy64]

SeasonLee, if the top FCF controls all of that, what does the lower one control?

 

[ewh]

"Without a datum reference, the size of the hex is being controlled." It refines the size.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[SeasonLee]

The lower FCF refines the size and form as indicated on the tip, you may use it to refine the location by adding the datum references(repeat the top datum reference).

Season

 

[jdomechanical]

orientation doesn't matter. pretend your 'across flats'(AF) dimension is a diameter (it is in the inscribed circle after all!) and treat it as a regular hole pattern.

we do this all the time.

 

[randy64]

jdomechanical, are you saying then, that what I put in my original post is what you would do?

 

[mkcski]

What about composite profile?

Certified Sr. GD&T Professional

 

[jdomechanical]

its what I would do and have done.

unless you need to control the hex holes orientation - that's a whole new ball game.

but you said round pins fit into them, so gauge it with round pins!

 

[WKTaylor]

Randy64

Suggest You detail the hex-hole planform and edges carefully: these aspects may be structurally important.

Are internal hex corners rounded-off [radiused] to eliminate stress concentration of a sharp-entry corners that might initiate cracking under pin-interference-pressure?

Are entry and exit edges chamfered or rounded-off [radiused] to facilitate pin entry and eliminate sharp edges that might initiate cracking or chipping... especially at the hex corners?

These details could be added to a basic 'sharp-hex' profile as 'typical' details.

NOTE.
Stress guys hate 'random orientations of sharp entry features' [corners]: suggest the hexes have a common hex-orientation in either an [X-Y] or [polar] arrangement.


Regards, Wil Taylor

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