Fixed Radius Circle?

Advanced techniques applicable to any version of CMM-Manager
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Fixed Radius Circle?

Post by Tking » Thu Sep 12, 2019 11:24 am

Is there any way to measure a fixed radius arc or circle in CMM-MANAGER? Description below.

(PC-DMIS - Feature)
FIXED_RAD Fixed Radius – This calculation type creates a circle of a given diameter, positioned so that the maximal radial distance from the data points to the circle is minimized. It is similar to the Max/Min math used in the MIN_SEP calculation except that,since the diameter is known in advance, the radius cannot vary. Only the circle's position is allowed to vary.
I could see where this is beneficial for measuring the position of arcs that are less than 180 degrees or circles with poor form. You could use a radius gage, gage pin or another more accurate method to determine size, then enter that size as a variable in CMM-MANAGER to force a best-fit to determine the position.


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Re: Fixed Radius Circle?

Post by medupriest » Mon Sep 16, 2019 11:07 am

This would undermine the fitting algorithms. There is a construction of a circle tangent to two lines with a set diameter, but not to a cloud. There is likely a VB solution if you would like to provide more details.

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Ryan Christopher
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Re: Fixed Radius Circle?

Post by Ryan Christopher » Mon Sep 16, 2019 1:07 pm

After some experimentation with measuring partial arc locations a few years back I did find a technique that worked. Your mentioning best-fit to do this is right on par with how it works.
1. Set up your coordinate system and sync to it.
2. Create a nominal point at the origin.
3. Measure the arc as points or cloud.
4. Use Cloud-to-CAD alignment to best-fit the alignment to the points. Use the locks to ensure the points only conrol the appropriate axis.
5. Translate the nominal distance over to where the arc should be.
6. Create a circle or point there.
7. Translate back to the origin point from step 2.
8. Sync Cad - add to program.
9. Report the arc location. (You'll have to type in the nominals)

This works in narrow situations where the best-fit controls only translation in 1 axis. I haven't tested any other ways to do it.
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Ryan Tackes
Applications Manager, VMS Inc.

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