On Saturday 24 March 2018 16:28:18 a k wrote: > Hello > It is sound strange but that what I have. > I build box 3 3 3 feet > And put all motor drive inside of it. > Why ? > This box build out of aluminum plate and holds together with bolts. > When all drive inside I have problem ==axis move by them self. > When I pull out all motor droves, they all working good. > I build this box to protect against outside magnetic noise = was > logical Right ? > But it is not what real situation . > > Something not ok, > Was I wrong with building aluminum box?
Probably not, I do it myself. But bear in mind that aluminum oxidizes very rapidly when the bare metal is exposed to the oxygen in the air, and this oxide film will be thick enough in .001 seconds to withstand a 50 volt potential difference between 2 sheets that LOOK as if they are bolted together, but in fact have no electrical connection between them. As opposed to bolts, drilling the correct holes of 2 different sizes, so that a sheet metal screw cuts threads in both sheets, will make a much better connection between the sheets, lasting longer. Not forever mind you, but for as long as a "gas tight" joint can be maintained. Giving the sheet metal screw a coat of "no-ox", a special grease that seals out the air, is a Good Thing. The only way for forever connections is to fold the box up from a single sheet, or weld it with a heliarc welder. Bolting is never to be considered a long time solution where you want a solid connection, it is so active a metal that its working to defeat your best intentions. The only reason it doesn't burst into flame (it will if finely powdered enough in an inert gas) is that the oxide film seals the surface, preventing more oxygen from getting to the aluminum. This by the way, is a good share of the heat generated when machining aluminum. Now, your ground MUST be a single bolt, preferably someplace near the center of the boxes back panel, preferably with star washers on both sides of the panel so the points of the stars will as they are tightened, cut thru this oxide coat and actually make an ohmic connection to the aluminum. Because aluminum "cold flows", if this bolt isn't stripped at 1 or 2 year intervals, and retightened again in order to re-establish the pressure to make the contact a gas free joint again, and then all your grounds re-installed on that bolt, and only on THAT bolt, so your once again have a good connection. I might add emphasis that a ground, disconnected from that bolt, is not to have any other path to ground, in other words, no continuity until that wire touches that bolt. Aluminum is a piss-poor metal to have in an electrical circuit, it takes care to actually use its quite decent electrical properties well. Haveing dealt with alu wire in some of the houses I have lived in, I will not ever consider buying a house that has alu wire any place on my side of the meter. Having it try to burn me to death along with the wife and 6+ children, even once, is once too many times. What really needs to happen at your site, is to get someone in there, with a decent dual trace 100 or more megahertz bandwidth oscilloscope to find out what is really going on. Something is seriously aglay there. An electrician is a good start, but what you may need is a Certified Electronics Technician because he will be more savvy about the trouble shooting needed. And he will likely own the test gear that the electrician may never have heard of. FWIW, I am one of those critters. :) But if I want a box thats electrically sealed, I start cutting panels out of double sided pcb material, and solder the edges. > On Mar 23, 2018 5:12 PM, "Gene Heskett" <[email protected]> wrote: > > On Friday 23 March 2018 19:24:58 a k wrote: > > > I am in portland . > > > 30 to 40 v ac I read between water pipe _ which is real ground and > > > ground on the outlet pin that has cylindrical shape. > > > Is this normal? > > > > No! > > > > But inspect that pipe, every inch of it all the way to real dirt. > > There may be a plastic connector, inserted someplace which will > > break that good ground connection. If so, jumper it from one side to > > the other with a solidly bolted connection using at least 10 gage > > solid copper wire. > > > > Water, depending on its purity is at best a poor conductor, although > > it can kill you, and really pure water (distilled or deionized) is > > an excellent insulator. > > > > > On Mar 23, 2018 4:03 PM, "Chris Albertson" > > > <[email protected]> > > > > > > wrote: > > > > Aram, > > > > > > > > Where to you live? In North America, UK, ....? > > > > > > > > Building wiring conventions are different in different places. > > > > but in general your system, taken as a whole needs to be > > > > connected to exactly ONE ground reference. No more no less. > > > > The best way to place a bolt some place and define that is "The > > > > Ground" > > > > And all static grounds are to be stacked on this single bolt. > > > > > > If you have 30+ volts AC on a ground pin on an outlet you have > > > > a problem that needs to be looked at by a good electrician. It > > > > should never be that high. Some cases are thinks like corosion > > > > and loose connections. One cause I that think of is that in > > > > some older buildings they were allowed to use metal conduit as > > > > the ground connection. Works OK at first but metal conduit > > > > rusts ofter time. > > > > > > > > Now day's we are required to pull a group cable > > > > with its own static ground in this cable. > > > > > > On Fri, Mar 23, 2018 at 2:04 PM, a k <[email protected]> wrote: > > > > > hi > > > > > i reassemble my lcnc mill, and i found that axis move by them > > > > > self. i think it is something to do with static electricity. > > > > > i found ground - and when grounded lcnc body of machine - > > > > > breaker turn > > > > > > > > off. > > > > > > > > > i measure with dc voltage between machine and ground 2. vdc > > > > > and when i measure ac voltage between lcnc machine and ground > > > > > it was 35 v AC. > > > > > > > > > > i know that when use real ground like a water pipe and ground > > > > > in outlet there always will be current they always be 30 v ac. > > > > > can it cause problem? > > > > Yes, and while I'm commenting on a plastic connector, its entirely > > possible that a teflon taped water pipe joint could be an insulator. > > > > > > > thanks > > > > > aram > > > > > ------------------------------------------------------------ > > > > > ------------------ > > > > > Check out the vibrant tech community on one of the world's > > > > > most engaging tech sites, Slashdot.org! > > > > > http://sdm.link/slashdot > > > > > _______________________________________________ > > > > > Emc-users mailing list > > > > > [email protected] > > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > -- > > > > > > > > Chris Albertson > > > > Redondo Beach, California > > > > ------------------------------------------------------------ > > > > ------------------ > > > > Check out the vibrant tech community on one of the world's most > > > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > > > _______________________________________________ > > > > Emc-users mailing list > > > > [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > ------------------------------------------------------------------ > > >---- -------- Check out the vibrant tech community on one of the > > > world's most engaging tech sites, Slashdot.org! > > > http://sdm.link/slashdot > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > -- > > Cheers, Gene Heskett > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author) > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > ------------------------------------------------------------ > > ------------------ > > Check out the vibrant tech community on one of the world's most > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ---------------------------------------------------------------------- >-------- Check out the vibrant tech community on one of the world's > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
