With three points on a circle you can determine the radius with a little bit of geometry. I can use the DROs on my mill to determine the coordinates of three points on each curve. The two end radii on the top cover in the right hand image of the cases (shown in the previous step) were 105.8 and 228 mm, too large for my templates. If the templates are well made then this can be quite accurate, however it can be time consuming if you need to try several templates before finding the matching one. To use, it is simply a matter of matching the curve to a template, this is made easier by shining a light from the back side. I am doubtful as to the usefulness of the very small ones and I mostly use the 25 to 50 and 52 to 100 mm ones. I have 6 sets of radius templates giving me a range of 0.3 mm to 100 mm, both internal and external radii. At the high end it would be a CMM and at the low end it will be Radius Templates (often called Radius Gauges). There are many ways to reverse engineer the curves, as always those available for any particular job are dependent on the size of the budget.
#RULER HALF WAY POINT MEASURE SOFTWARE#
I also include a link to some software that I wrote to calculate the radius for any size measuring device. Do not worry or stop reading, I present a graph for reading the radius knowing the gauge displacement. The cost of my design is just that of a digital or dial gauge, the downside is that the reading needs some manipulation to get converted into a radius measure. This allows the use of a standard mass produced digital display to display radius directly.ĭuring a quiet moment I decided to make my own digital gauge based device and the main thrust of this Instructable is to describe just that. The jaw angles of the digital calipers are chosen so that the opening displacement is equal to the radius. The vernier calipers achieve the same by using an appropriate scale. The commercial gauge above is not a standard digital gauge, the display is multi-line and the gauge will have special firmware to calculate and show the radius directly.
In fact this three point method is how the above commercial gauge and calipers function. With three points on a circle you can determine the radius of a curved workpiece with a little bit of geometry (see a later step). These special commercial gauges and calipers tend to have starting prices of several hundred dollars.
The first illustration above show what I made and the other photos show some commercial offerings to do this job. I needed to measure the radii of several curves so that I could write some G-code to direct a CNC mill to trace out the same shapes. I needed to duplicate some curves from a 1960s racing motorcycle crank- and gear- case to a new set being milled from the solid.
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