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Documenting a Polygon with Rounded Corners

11/11/2021 4:07 PM

Adding dimensions to a square or rectangle with rounded corners is easy. In addition, a Quality Inspector can measure fabricated parts with vernier calipers and a radius gauge.

A six sided polygon is more of a challenge. The overall X and Y dimensions are easy to document and measure as shown below. The lower two corners can have their radius documented and produced parts can be QC checked in a similar manner as shown above. The remaining straight sides (black) and corners (red) are more of a challenge. The intersection of sides has been cut away by the rounded corners and the obtuse angles prevent easy assumptions of "horizontal" and "vertical".

Documenting this for fabrication in a manner that is supportive of Quality Control Acceptance Tests (measurements) at production time makes this even more of a problem. How would you do it?

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#1

Re: Documenting a Polygon with Rounded Corners

11/11/2021 7:06 PM

You make a cutout that the piece will fit in, within spec, then check for any excessive gaps with a feeler gauge...

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#2

Re: Documenting a Polygon with Rounded Corners

11/11/2021 8:26 PM

Maybe measure with one of these?

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#3

Re: Documenting a Polygon with Rounded Corners

11/11/2021 8:54 PM

How about documenting it?

It almost seems like I need virtual points "out in space" which indicate where the corners would have been if the corners were not rounded. That makes logical sense but I don't think I have ever seen it on a drawing.

This is probably going to be easy and make my question look foolish. But somehow it seems like all I remember are items made from circles, squares, rectangles or shapes so odd that solid models are provided and features are not dimensioned. If the angles came down to a sharp intersection then this would be easy. Coming down to a rounded shape makes my intersection point in free-space. I just don't remember doing that on a "proper mechanical drawing".

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#4
In reply to #3

Re: Documenting a Polygon with Rounded Corners

11/11/2021 10:03 PM

I think you work from the endpoints and determine the radius of the turn for the corners...

So you determine the radius of a turn by picking the two end points and measure the distance between them, then using each endpoint draw a circle with that as a radius and where the two circles intersect is the radius center point....

So all your measurements are from the endpoints of the radiused corners and middle points of the radiused turns...

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#5

Re: Documenting a Polygon with Rounded Corners

11/11/2021 10:24 PM

This might help.

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#8
In reply to #5

Re: Documenting a Polygon with Rounded Corners

11/13/2021 8:07 PM

Thanks for the video link. It is directly on target. After watching the video link I Googled the video's term "fillet sharp". It seems to only give me info on sharp knives for cutting fish. Having to use a virtual point is easy to understand. I just didn't know how to defend it with an ASME or other reference. I also didn't know if you leave the point blank or draw in a point (not likely) or cross hairs.

Thank you.

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#10
In reply to #8

Re: Documenting a Polygon with Rounded Corners

11/14/2021 7:04 AM
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#6

Re: Documenting a Polygon with Rounded Corners

11/11/2021 10:26 PM

There might be a way to document and check the shape before the corners are rounded. Then use one or more radius gauges to check the rounding of the corners.

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#7

Re: Documenting a Polygon with Rounded Corners

11/12/2021 3:24 PM

You dimension to the virtual intersection of the two edges. A coordinate measuring machine (CMM) can easily locate this point and give an accurate measurment.

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#9
In reply to #7

Re: Documenting a Polygon with Rounded Corners

11/13/2021 8:09 PM

Thank you.

Any references (ASME, etc.) that I can quote. I especially would like to justify against a standard having a blank virtual point (or cross hairs if per standard).

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#11
In reply to #7

Re: Documenting a Polygon with Rounded Corners

11/16/2021 7:30 AM

Had a demo of this measuring system a couple of weeks ago as a possible upgrade to our existing vision measuring system. It would measure & document that part within 5 seconds.

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