Kirk Wallace wrote: > An encoder able to operate in a chip free but oily environment is what I > am seeking. I put a spindle tach on my Bridgeport, picking up teeth on the 81-tooth bull gear in the head. I used a gear tooth sensor out of a Honeywell line printer. I think it is magneto-resistive. The front of it is entirely covered in thin aluminum. 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. > Truly sealed encoders are available, but they are pretty expensive. > 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? > My guess is a permanent magnet and a coil of wire. A vane or whatever alters the magnetic path. They probably have a tooth or slot with a different width to indicate cylinder 1.
I tried to build a magnetic sensor pickup for a lathe tach, making a 60-toothed wheel out of steel sheet. I was never able to get it to work, and finally figured out the Hall sensor element was set up for a very wide sensing area. The teeth were too small to properly sense each one. I dropped back to an optical slot sensor and it works fine. Adding another slot sensor for a B channel and an extra tab and sensor for the index pulse would turn it into a full-fledged ABZ encoder. When I CNC the lathe I may very well do that, as it is big enough to fit around the spindle, rather than belt-drive a standard encoder. Jon ------------------------------------------------------------------------- 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
