On Tuesday 04 December 2007, Kirk Wallace wrote: >On Mon, 2007-12-03 at 20:58 -0500, Gene Heskett wrote: >> On Monday 03 December 2007, John Kasunich wrote: >> >Gene Heskett wrote: [...] >> 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.
The diesel engine folks, who have a ready supply of fancy oil to keep the lips wet with, have been doing this for many years. Might need 3/8" of exposed shaft for one of those. >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. The best scenario. >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. One might consider recovering those with the usual $5 a tube silicon caulking, its available in clear. >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. Amazing, considering my experience. >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? Was halls a few years ago, no idea at the present. >Fortunately, what I have currently, is working, but that doesn't mean I >can't try to improve something until it doesn't. That old saw about "not fixing something which isn't broken" comes to mind. :) As above, I am aware that halls have been used to good effect as engine crankshaft position detectors in automotive ECM apps for quite a few years now, with minimal failure rates. So there appears to be a disconnect between my observations and the rest of the automotive etc industrial use of hall sensors, and I can't come up with a sensible explanation for that disconnect. The particular devices that failed like Orville's popcorn were made by Microswitch, and the keyboard itself was a Cherry, specially built for the Beston Marquee character generator, and had a replacement cost from Beston of about $500. The active element in the key was fabbed on a 3/8 square ceramic substrate with a blob of epoxy B covering it, and the key driven magnet slid onto the bottom of the ceramic when the key was depressed. It may be that this particular ceramic was slightly porous, and that other makers devices are better sealed. But it looked to be the usual berylium oxide, the same stuff used for a glass replacement in hi powered transmitter vacuum tubes, and not even air gets thru those else they're instantly several thousand dollars worth of junk. I don't recall now if there was the usual paper in the replacement switches boxes warning about the use of the berylium though. Never grind or abrade that stuff, a particle inhaled is a ticket to lung cancer in a few years as it never goes away and continues to irritate on a microscopic scale. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) I know you think you thought you knew what you thought I said, but I'm not sure you understood what you thought I meant. ------------------------------------------------------------------------- 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
