On Thu, 1 May 2014 10:15:48 -0700 (PDT), wrote:

On Thursday, May 1, 2014 12:12:52 PM UTC-4, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

The thing needs to work with a model airplane engine, so it's going to be
a high vibration environment.

The easy to get magnets (which is what I have) are nickel plated, so
they're slippery as hell. They're also not machined to super-tight
tolerances, and NdFeB is brittle as hell (it's optimized for magnetic
hardness, not physical strength!).

The best I can think of is to drill the hole to a slip fit and then
epoxy. I have visions of actually achieving a press fit, then watching
magnet after magnet crumble into clinging dust trying to press them in.

Suggestions?

Maybe an over size hole, epoxy and then a cover plate/tab that's held with a screw.

What's your detector?
Could you use an LED and photo diode?

George H.



--



Tim Wescott

Wescott Design Services

http://www.wescottdesign.com
Works good with a reflective spot on the back of the spinner and a
photo-tach. Or like a lot of the model plane guys do, a shiny tip on
the prop, and a phototach reading out at the tip instrad of at the hub
- better chance of getting accuracy at speed.