The default is “100” and the slider will change the value of the radius, obviously making the polygon larger or smaller, but 100 what?

It is clearly not millimeters because a setting of 100 results in a polygon that has a radius of about 22 mm

It is clearly not 100ths of inches, for the same reason.

Am I asking this question in the wrong place?

I am assuming that the radius in the app refers to the radius of the circumcircle, not the incircle.

I threw the question out to some students who developed a procedure to try to “calibrate” the polygon tool. We will run a test carve series in MDF, creating a series of n side polygons where n is divisible by 2, and labeling each with selected values for R. (Not a mathematician, but I believe R refers to the Radius of the circumcircle while r is the radius of the incircle).

This should give the students a table of values from which they can derive formulae to calculate incircle and circumcircle radii for a given input for polygons with even numbers of sides.

With some basic data, they should then be able to derive a formula that can calculate incircle and circumcircle radii for any n sided polygon, and then we can carve a display “tile” that explains the radii of polygons.

And to think this all stated because I was making a dust extractor…

Ain’t technology just the coolest?

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Oh, and I thought it was cool that the students figured out that we needed to start with polygon with an even number of sides because the Diameter of a polygon with an odd number of sides ends at a vertex on one side, but bisects the opposite side to end at a tangent point on the circumcircle.

This is precisely the kind of inquiry I had in mind when I talked the school into buying me an X-Carve.

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Hey @ChristopherDahle

Those values are pixels, which are scaled after importing the shape. I need to convert the app to the new app api version we have (`2.0.0`

) before that slider can represent real-world values. Currently that value would translate to 96 pixels/inch.

Thanks Eric, 96 pixels per inch will give us the means to produce a conversion formula that I can put on a poster near the machine.

My students came very close to the real measurement, they took the average from a series of measurements and came up with 100 “mystery units” = 26 mm, so they were within half a millimeter. Not bad for 11 year-olds!

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@ChristopherDahle Hey Chris, I updated the polygon generator app. It now uses inches as the radius’ unit!

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Thank’s Eric! We have used the app since you made the change and it works perfectly.