Is there a way to accurately determine this radius?

[OTmachine]

The OP asked for a way to accurately measure the radius of a fillet. The method that I proposed in post #9 will determine the radius to within a few thousandths.

There is an instrument used in optics called a spherometer which will measure the radius of a spherical surface. It consists of three points on an equilateral triangle and a fourth adjustable point at the center of the triangle.. The instrument is placed on the surface of the sphere with a ll four points touching. The distance the fourth point is above the plane of the three points determines the radius of the sphere.

I made a 2D version of this which will measure the radius of a cylindrical curve. It is essentially two points a known distance apart with a third adjustable point midway between the first two. Like the spherometer, the third point is adjusted so all three points are touching and the distance of the third point above the line between the first two points determines the radius. This can be used for both positive and negative radii.
View attachment 452904
It is much like a depth mike except the bar is replaced by the two points.

The radius of a curved surface, r, is given by the distance of the midpoint, h, above the line between the two outpoints, separated by a distance, d as r = (d^2)/8h +h/2. This device is particularly useful for large radii where only a small portion of the curve is available. For more accurate measurements, the screw would be replaced with a micrometer barrel.

Not trying to be critical. Looks like the same method as in post #14 basically?

 

[RJSakowski]

Not trying to be critical. Looks like the same method as in post #14 basically?
I have trouble seeing how to apply that to a corner radius.

We always used product of the means = product of the extremes using a perpendicular bisector, (diameter of circle). Use a known length straight edge to make an internal chord, then measure the depth at mid-point of said chord.

I am having trouble seeing how to implement that on an outside corner fillet without some sort of tool as I have described without some sort of tool as I described.

 

[RJSakowski]

Sorry to post what at first seemed logical without checking first. Thanks for checking.
Does the figure 0.5825xD apply to all cases? if it does, that is a handy number.

The number will work for any size radius.

 

[sdelivery]

I use radius gauges for measuring radius.
I rebuilt an old truck bed that had a radius at the top by using hydraulic tubing that I welded to the edge. With a little effort it was strong and nearly invisible.

 

[Parlo]

I use radius gauges for measuring radius.
I rebuilt an old truck bed that had a radius at the top by using hydraulic tubing that I welded to the edge. With a little effort it was strong and nearly invisible.

I use radius gauges to measure radii too... Anyone else discovered these.?

 

[OTmachine]

I am having trouble seeing how to implement that on an outside corner fillet without some sort of tool as I have described without some sort of tool as I described.

Measure inside the cabinet. Or use a contour gage then the formula.
”Most“ radius gage sets are too small for this. Probably about a 2” radius. To keep it simple, I set my dial caliper at 2.00” outside measure. Checked the depth from beam to tips, (1.500”). Set caliper points on arc of radius. Used a 6” (100ths division) scale to measure down to the contour at the 1” mark on the caliper beam.
Probably too long winded. I’ll stop here.