Re: [CAD_CAM_EDM_DRO] Machine mounted Tachometer with Surface Meter Per minuteThis

On 09/11/2010 06:59 AM, Will Holding wrote:

> I would go for optical off of a white painted half of the rotor shaft tail end at the tail bearing. I don't think Hall is going to be easy to make work with the stray electrical noise at router speeds and I think the proximity required off of the nut would make bit changes challenging. Hall is great for slow speeds, because it does not require any speed at all, not like an inductive pickup where the parts have to be moving.
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> I'm not sure response speed rules out hall because I know automotive applicationa like Ford's EDIS, use a 40 tooth wheel and read fine to 6500RPM, so thats 260K CPM which would easily allow for a divide by 8 at 30K RPM, divide by 6 should allow plenty of overhead. But a chopper wheel on the shaft above the nut IMO would make it a heck of a lot easier to do bit changes- could also have a negative effect on cooling airflow though.
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> AFAIK taking an optical from the tail end of the shaft where you can simply drill the housing to expose the shaft and paint half while and point a laser tach at it with a $25 BOM sounds like it's worth a try- if it doesn't work all you have done is drilled a superflouous hole in the router case, and if it does work you have saved yourself a lot of hassle with bit changes and other potential issues.
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> My. 02
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> -Will
>

You make a good point about tool changes and electrical interference. I
don't know if the Hall sensor will be affected by the electrical noise
and it would, of necessity, either be mounted above the nut or be
movable or be in the way...

Many router spindles have some form of spindle lock which locks the
spindle so the wrench can develop torque to loosen the collet nut.
Perhaps the sensor could look at that cut/nut offset from the spindle lock.