Hemisphere and Plate motion sensor mount. Simple and elegant

Back in August, everlith posted ‘DIY motion sensor mount’. Everlith sparked an idea I call the ‘hemisphere and plate motion sensor mount’. The completed mount consists of a 1” ø hemisphere and a 1-9/32”x1-9/32”x1/4” plate made of acrylic or PVC plastic. Earlier trial mock-ups of a motion sensor for my driveway/garage door configuration indicated a 30° from vertical works best. It picks up front sidewalk and driveway activity and doesn’t sense street traffic. Some shop tools and fabrication abilities are required or a friend/relative with such. I start off showing the finished product with subsequent pictures depicting intermediate steps. In the pictures ahead, some interesting methods are shown.

The finished 30° motion sensor mount. If you wanted a vertical mount only the plate would be used and the hemisphere would not be needed.

These four pictures deal with acquiring and holding the 30° angle while drilling the hemisphere jig. Use a spade drill bit with flat-across cutting shoulders. Of course, if you have a drill press with a tilting table the angle rigging depicted here can be dispensed with.

This group of pictures shows that the hemisphere should protrude 1/6” or a little more beyond the surface of the jig face. A hemisphere protruding more than a 1/16+” should be further drilled. If the hemisphere is lower than 1/16” small pieces of tape or paper can be placed in the bottom of the hole to shim it up to proper projection. Picture 7 shows a center-cut kerf so a C-clamp can be used to make the jig grip the hemisphere.

Pictures 9 shows a precise way sanding in a flat surface to the 30° angle. Picture 10 shows the initial swiggly sanding checkmarks are barely visible, indicating a uniform sanding. As you sand frequently check the checkmarks, adjusting hand pressure on the jig as needed. Also, the alignment prick marks are shown to help with proper assembly next.

Pictures 13 and 14 assembly alignment with the temporary machine screw and being glued. The next two pictures show preparations for installing the mount.

Ready to mount the motion sensor.
Thats all folks.
Victor Maletic