On Monday 20 August 2007, Jon Elson wrote: >Gene Heskett wrote: >> Greetings everybody; >> >> I was working on the frame for my new z axis drive for that micro-mill, >> and have managed now to break off not one, but 2, 6-nc32 taps in the holes >> drilled into the edge of a piece of 1/4"x1.5" steel bar. >> >> I now have the work insulated, a copper wire in the chuck bent to wobble >> about enough to cover the ends of the taps, and tried a 50 volt AC supply >> for about 20 minutes, but the transformers were way too puny and have >> already smoked. I have an air jet blowing on the work, and the wire >> running about 200 rpm. While it worked, I'd guess I got rid of 5 thou >> total, from the work and the electrode wire end, so its not gonna be >> exactly a 5 minute job unless I can get some more effective firepower into >> it. >> >> Figuring that DC, with a current limiter of sorts and a storage capacitor >> to hold more bang will probably work better, I've resigned myself to >> building it. >> >> The question then is, for an air quenched lashup, what is a suitable >> voltage, and a suitable current limit in terms of average milliamps, that >> I should try and build? Googleing doesn't seem to spit that sort of info >> out readily. > >Look at my info at http://jelinux.pico-systems.com/edm.html >You need a current-limited supply of DC to a film-type capacitor >to deliver the current pulses that do the EDM work. Also, I >think a dielectric fluid is really important to make the >difference between welding and EDM. I run 30 V at about 1 A, >mostly due to the parts in my EDM power supply. I found >alum-tap (an aluminum tapping fluid) works great, although it is >flammable. I only keep a couple drops of it in the hole at a >time to reduce the risk of a big fire. (I did get it to flash >once, but it did not sustain a fire, so it must have some fire >retardant or vapor suppression in it.) Water won't work unless >it is really pure. Some people have reported plain distilled >water works well. > >Jon
Thanks Jon, that is about what I was looking for. I noted that the wiki seems to indicate an rf generator is often used, with frequencies around the 500 khz range. That almost sounds as if it would setup a plasma that would never be quenched. And while that might cut at a higher rate, this sounds a whole lot simpler. Is the quality of the capacitor that important? I see you wrote film in the text, but showed paper on the drawing. I can borrow a big oil filled can with 8 or 10 uf, rated at 8 to 10kv from our transmitter spares. My motor psu is 29 volts, and if I can cobble up a suitable limiting resistor, and in this case a 100 watt light bulb comes to mind as it will also light dimly to show the short status, then that home-made psu can serve as the current source. It can certainly spare that portion of an amp. I don't have anything that looks or sounds like aluma-tap, but I can certainly source a gallon of distilled water, or I have a quart of ACE hdwe thread cutting oil which will probably work, and has already contaminated the area. I didn't have any plastic rod to hold the wire, a hunk of 14 gauge from some handy romex, so the work rather than the electrode is insulated, a couple pieces of scrap formica are padding the vise jaws & a small strip of cherry under the bottom edge. No leakage that I can measure. Slightly shocking to the touch though, I allowed my sweaty arm to lay on it at one point. :) The wire is currently rotating with a small clip lead attached, which seems to work but shows some wear where the clip sits already, but I like the idea of the much stiffer brass, so I'll see if I can src a hunk of smallish brazing rod while I'm out doing the honeydo's this morning. What I have on hand is too big, 1/8" IIRC, so I didn't even think to dig it out. 3/32" would be ideal I'd think for a 6-32 taps web diameter. But with the depth I have to go, probably nearly 3/4" for one of them, the cleanout will probably have to be done with an air hose after I get down the first 1/8". Might even have to rig a stinger from a wd-40 can somehow and get right into the hole. Fun and games... With an air jet and 50 VAC with no capacitor, I was only able to go with a f0.0003" feed. If I can get 0.010"/min out of it, that would be great in comparison. Thanks Jon. -- 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) There's a fine line between courage and foolishness. Too bad it's not a fence. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
