Whoa! Don't tip so far!

I finished up that job where I broke the half inch end mill, and now I'm on to the next one: a switch.

We've got a piece of equipment that shouldn't tip over beyond about 70 degrees off vertical. We needed a switch to tell us if that happened so power to the equipment's motors could be cut. There are all kinds of digital sensors that can be used to do the job. A good case in point is a three-axis accelerometer. Spark Fun sells these for not too much (about $100 US per axis). The idea is that in an object at rest, you should get some vector sum of your three orthogonal axes that equals 1g of acceleration. The direction of that vector is "down". If your "down" drifts too far off your Z axis, you've tipped beyond your limit.

Buuuuut such things require math, computer processing, and reliable software and hardware. In essence it's a sensor, but it's not a switch. What we wanted was a switch. Even if the computers go wonky, we need the switch to still be a switch.

The rendering above is what I'll start making on Monday. With any luck I'll finish it on Monday, too. It's a cone, cut to a 40 degree inclusive angle, with a ball in it and an inductive proximity switch set to trigger at the presence of the ball. Tip the cone more than 70 degrees off vertical, the ball rolls away, and the switch opens up. Voila: The tippy-switch.

It should be pretty fun. The inductive switches are threaded M12x1, and the cone will be cut as a single part. The cap is just a slice from the same round, or a piece of 1/4" plate cut down to size and drilled for screws. Once the cone and cap are finished, the flat and mounting screws can be machined on the mill.

But the real fun for this will be the long tapered bore. I've done some smaller tapered bores when I was making rocket nozzles, but this will be bigger than any of those. (In case you want to see a tapered bore getting cut, watch October Sky with Jake Gyllenhaal and Laura Dern. At one point Leon Bolden, played by Randy Stripling, cuts a tapered bore in a rocket nozzle for Homer Hickam, played by Jake Gyllenhaal, and calls his attention to it. Can't miss it.)

I'll post a picture of the switch once all the bits and pieces are finished. But the real test will be wiring it up, bolting it to a rotary stage, and finding out if it really ticks over at 20 degrees off the horizon.

Can't wait!

Tom