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

I have only seen small routers that have this spindle lock (2HP or less) and it's usually a bar that slides in and out with a keyhole shaped hole in it that engages flats on the spindle shaft. This configuration does not leave any way I can see to mount such a sensor.

I'm inclined to go with the easy (10 minutes) cheap ($20) attempt I described earlier- if something fancier is needed then there are other ways it could be accomplished. Other such ways might be to open up the router case and modify the fan turbine to work with a hall sensor (say cutting back all but two opposing blades about 1/8"), or to use the spinning magnetic pole of the rotor itself to fire an inductive pickup.These latter methods are "isolated" from the motor's electrical field but still magnetically coupled and I'm not sure how immune they would be to noise. Plus, having even a working hall sensor is useless unless you also make a driver for it and ultimately, some sort of display. The non-contact laser unit takes care of all this for you, out of the box. I haven't taken one apart but it would probably not involve a whole lot of drama to remote the sensor from the display either.

I have not seen the model plane ones the other guy mentioned or how they are set up, they might be better still for all I know.\

Sometimes it's tempting to build a sexy custom "industrial grade" thing (guilty here too) and sometimes it's better to adapt some cheap ready made product in the interests of getting the job done. I don't know if one approach is "right" and the other one is "wrong" , but one guy will be likely making chips while the other guy is still soldering wires or online ordering schmidtt triggers from digikey to make his driver work. I have computer generated invoices and one of the guys I often work with hand writes his on paper. Mine look a lot nicer but I noticed when we sign a deal he leaves with a check, and I leave to go print an invoice. So I don't really know if my more "professional" approach is really better or not.





-Will

----- Original Message -----
From: David G. LeVine
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Saturday, September 11, 2010 12:13 PM
Subject: 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.
>
> 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.
>
> 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.
>
> My. 02
>
> -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.





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