method to determine radius of three points
gsp56
| Posted in Jigs, Fixtures, Tips & Tricks on
Some time back, I was shown a method to determine the radius that included three points any distance apart. This process is very helpful for creating the right arc for a given piece and involved swinging radii from the three points and their intersections. Unfortunately, I lost the piece of paper that described the exact formula. I’ve spent a good deal of time on trial and error and also searched geometry resources with no success. Anyone know this trick?
Replies
Drawing Large Radiius Curves
Ask and you shall receive. I've seen several formulas and thought them so useful I made my own drawing which hangs on the wall in my shop. I took a picture of same and attached it to this post. Let me know if you need clarification.
Pete
Thanks! Your method is more straightforward than what I had been shown. No math was involved, just drawing arcs from various points. I am glad to have this formula in my toolbox again!
No math
Draw a straight line from the point in the middle to each of the outer points. At the midpoint of each of the two lines you just drew draw a new line at a right angle to the line connecting the points, where the two lines intersect is the center of your arc.
SAS
I hate side angle side proofs.
I take great relief, therefore, in the fact that theorems can't be proven.
This is different from the no math way I had been shown, but simpler by a long shot. This process has an advantage over the math formula described above in that the middle point does not have to be center and representative of the full "rise" to calculate the radius.
This forum post is now archived. Commenting has been disabled