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

Gaston Gagnon wrote:

> Hi David,
> On 2010-09-10 22:09, David G. LeVine wrote:
>
>> On 09/10/2010 10:49 AM, Gaston Gagnon wrote:
>>
>>> Yeah, I know, I will have to take the plunge: open up the router, install
>>> something (?) and make hole in the body for the sensor but I was hoping
>>> (secretly) someone would come up with a way to derive the actual speed from
>>> router's internal speed control electronic. ;-)
>>> Gaston
>>>
>> Most routers have a nut at the collet. If using non-ferrous metals (or
>> wood or plastic), a hall effect sensor can pick up the points or cuts
>> (for ER type collets.)
>>
> Can you elaborate a little on how this would work since Hall effect sensors
> are only sensitive to change in magnetic field.
>

I think he means if the workpiece material is non-ferrous, then a Hall
sensor can be used
to pick up the points on a steel collet nut. This will require a magnet
to bias the sensor, so
steel chips would be attracted to the magnet. I can't imagine anyone
cutting steel with
a router, anyway. I think the points on the nut don't protrude enough
to make many Hall
sensors work well. Most are area-sensitive, and I had a lot of trouble
getting them to detect
anything smaller than half an inch wide. One Hall sensor that does work
is the Allegro
ATS667 family, available from Digi-Key. I ised the ATS667LSGTN-T but it
may not be
readily available right now. Allegro has some other related models that
work the same way.
These have two hall sensors a couple mm apart, and compare the signal
from both. They work
very well to detect fairly narrow gear teeth. They have one HECK of a
magnet embedded in the sensor,
so any ferrous dust will definitely be attracted to them.

Jon