On Mon, 2007-12-03 at 20:58 -0500, Gene Heskett wrote: > On Monday 03 December 2007, John Kasunich wrote: > >Gene Heskett wrote: > >> On Monday 03 December 2007, Kirk Wallace wrote: > >>> Has anyone tried using a magnetic sensor such as a crankshaft position > >>> sensor for a spindle encoder? I would not have to protect this ... snip > >would fall off or be easy to wipe away. Chips and permanent magnets are > >not a good combination, seems impossible to keep clean. > > > >Regards, > > > >John Kasunich > > > Not to mention John, that hall effect devices are poisoned and rendered > useless, often in just a day or so by even the hint of a petroleum based > lubricant that might get splattered on them. And they are commonly built on > a ceramic substrate that is a bit porous. I believe moreso than the epoxy B > covering the top of the device. I once lost a very fine character generator > keyboard for over a week cuz it got a lot of grit in its keys after several > years service and gave it a good washout with WD-40. Three days later, and 9 > dead keys, I called the maker and while ordering the keyswitches at about $12 > ea, I was instructed to run, not walk, to the corporate kitchens dishwasher > and run it thru at least 2 cycles, once with the usual dishwasher powdered > soap, and once more to rinse it well. In the top rack. That stopped the > keyswitch failures after about 2 more. > > So the short message is: Keep your hall effect devices scrupulously clean. > And > not with solvents, good old soap and water.
An encoder able to operate in a chip free but oily environment is what I am seeking. There is about a .030 inch gap between the spindle shaft and the encoder housing, on the spindle belt side and the collet closer side. It appears that in the past a fair amount of oil was dripping into the lower half of the lathe and get flung about by the spindle belt. Some of this oil seems to have found its way into the encoder enclosure. Then of course there is oil being flung about in the work area. Oil, on occasion, may get splashed on the collet closer and again find its way into the enclosure from the closer side. I thought about adding seals, but there isn't much space for seals, and I have no experience in keeping 2.5 inch diameter seals alive at 3,000 RPM. An option is to not have seals and have an encoder that could tolerate a small amount of oil that may find it way in through the gaps. My lathe turret encoder is an array of hall sensors, originally encapsulated in some sort of clear rubber or silicone. From bad pneumatic seals, since replaced, oil was getting sprayed onto the encoder and the encapsulation was degraded to the point of falling apart. Since the encoder was still working, I decided to remove the rubber and run it without protection. So far, so good. My home and limit switches are all Hall sensors. The Z axis sensors are encased in an aluminum barrel and potted in what appears to be epoxy, which should be pretty good protection, but the X axis switches are Hall type lever switches, which where filled with oil when I took them apart. I cleaned them, reinstalled them and they are working fine. Though I can sympathize with oil being the bane of Hall sensors, _my_ experience so far has indicated otherwise. I am planning on using Hall home and limit sensors on my Bridgeport, which will be sealed or potted in aluminum enclosures. I could do the same with the lathe spindle sensors, but I guess finding a sensor that is fast enough is a problem. An automobile crankshaft sensor should be fast and rugged enough. I wonder, what sensor is used there? Fortunately, what I have currently, is working, but that doesn't mean I can't try to improve something until it doesn't. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
