One of the things I'm doing in preparation for the JOTA event on the USS IOWA, is (finally!) building up my new "more portable" antenna mount for my satellite antenna.
I started with a 5' surveyor's tripod I got really cheep on eBay. I have numerous "spare" Yaesu Azimuth/Elevation rotators and control boxes, so I figured I could mount one of my spares to the tripod with an adapter plate.
I bought some good 6061 1/4" thick aluminum sheet, and proceeded to cut out a 6"x6" square. I marked it, and using a set of trammels, laid out a circle the same diameter as the bolt circle for the Azimuth motor. Then I drilled and countersunk some holes to bolt it to the motor with flat-head machine screws.
Now the task was to mount the plate to the tripod, and there was the snag I hit.
The top of the tripod is triangular, and where the legs mount to it there's a lack of space on the underside of the plate to use four mounting screws. So, I decided I'd use three screws instead, and they'd have plenty of room between where the legs meet the top of the tripod.
The problem was, how do I lay out 3 equally spaced holes on the correct 3" diameter circle I just scribed using my trammels?
I remember from way back in high-school geometry (or was it trig?) that dividing a circle into thirds was a very complex, tricky task, and you were better off to just get a protractor, and lay out your marks every 120*.
A quick Google search found this very ingenious method of equally dividing a circle into three sections, WITHOUT the use of a protractor.
I was so amazed that I thought I'd share it with my friends here, in case any of you are metal cutters like I am, or perhaps woodworkers.
Enjoy the little video. I found it quite amazing!
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Okay, so how does one place the point on the diameter line? Move to the right or left will make the angles bigger or smaller????
ReplyDelete1/4 of the diameter will give you 120 degrees, I don't remember the math for the rest of it though... :-(
ReplyDeleteOld_NFO beat me to it. i/4 the diameter is half the radius, so I went half way between the center of the circle and one edge of it. From that point you draw a line at 90* to the radius/diameter, crossing both edges of the circle, and those two points are 120* apart.
ReplyDeleteIt's harder to describe than watching him do it.
The process was easy, but I didn't know until now that the perpendicular line was set at 1/4 the diameter. Cool trick!
DeleteWhy not devide it into 6 parts. Easier. Thanks use 2 parts times 3.
DeleteThe only 'trick' to it is making your measurements VERY precisely.
ReplyDeleteI was off a tad, and while it worked just fine for what I needed, the marks I made were not exactly 120* apart.
After playing around with pencil and paper, I saw that an error of even a small amount would result in a larger error in the "equality" of the 120* spacing.