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Using an EDM on vertical surfaces

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  • Using an EDM on vertical surfaces

    I have a broken 1/4" tap in a grease fitting location on the vertical surface of a forklift mast. Can an EDM be used in that location?

  • #2
    No. EDM's are about the size of a milling machine and have a tank of fluid (dielectric) that the part is submerged in.

    You can drill it with a Hi-Roc drill (solid Carbide for drill die steel) if you chuck it in a magnetic base drill - the reason for the drill is the carbide drill bits are fragile and any side movement will shatter them like glass.

    The other option is a die grinder with a 1/8" solid carbide burr - using it to carefully grind the center section of the tap out so the flutes can be removed with pliers.

    If you have a good welder, you can sometimes wekd a nut to the tap and extract it that way.

    If you bugger the hole, don't worry, helicoil and steel inserts are available if you end up mangling the hole (downsizing new threads).


    • #3
      Practically, Thrud is probably right, but the large EDM with integral tank is not a requirement. There was a picture of the Langlois EDM in HSM removing a broken stud from a snow blower engine. He was using a brass tube electrode and feeding water through the electrode. The only tank was a clay dam around the stud, holding probably less than an ounce of water.

      The fluid probably has something to do with how well the sparking works, although the fact that you can use either EDM oil, or distilled water, or in some cases even tap water, suggests that the spark isn't too picky about the fluid. The main requirement is to flush away the eroded material. So yes, if you have an EDM with a remote head like the Langlois, and can keep the working face of the electrode immersed in fluid while you feed it horizontally into the vertical surface, it should work just fine.


      • #4
        Uncle Dunc:
        You are right, but I thought he might be in a bigger hurry than to order the "Build Your Own EDM" book From Village Press, wait for it, build it and then do it. It might be quicker to build a forklift from scratch!


        • #5
          Thrud and Uncle Dunc--thanks for your responses to my question. Someone had already tried to remove the tap and all I was left was a shallow crater. I have thought of making the edm in the recent issue of MW. Is the liquid used for cooling,prevent spattering,maintain integrity of electrode,carry away debris, noise abatement, or all of the above??? Paul


          • #6
            It is coolant, dielectric (insulator), and helps to clear vaporized metal/carbon. Without it, you are just welding. It is an essential part of the process. The sparkgap between the work and the electrode is quite small and the dielectric (can be a commercial fluid or can sometimes just be distilled water) helps to localize the action.


            • #7
              I have trouble shot several EDM. Vacuumm tube types. I remember lots of capacitors, tubes and Potentiometers. Never measured the voltage nor frequencies of any. I've looked for links that give such info, found none.

              Best I remember, the arc voltage, once the arc is established is rather constant even with different arc lenghts. That implies to me that the establishing voltage must be high enough to break down the die-electric. higher frequencies would seem to cut faster, but the arc has to extinguish? Elucidate for my edification please.

              Any one have a link? Anyone know what the voltages run? What is a common frequecy used in the professional stuff??


              • #8
                High frequency arcs help to break down insulating oxide layers in materials such as Aluminum - in the same fashion as a TIG welder. Polarity can be adjusted in plunge EDM to change the erosion action and sometimes clearances. Clearances are often done by allowing wear to take its course - so wehn you start a plunge cut into a stripper plate/die sandwich one has more clearance than the other, and the plunge electrode ends up actually being the punch (sneaky buggers).

                they can adjust Current or voltage just as a welder can. The process is arc welding without metal deposit - rather removal by the dielectric the vapourized metal in the arc gap. Without dieletric the arc would just form a big puddle of molten metal. The key to its control is the dielectric and the constant arc gap.


                • #9
                  Doc Steve;
                  The machines I am familiar with ( 4 different mfgrs) have voltages of 80 to 105 volts.the frequencies are variable to suit the cutting rate and other parameters such as surface finish and recast.Hope this helps.


                  • #10
                    Thanks Bill. Numbers was what I wanted, numbers you gave.

                    The old vacuum tubes were high voltage, high output impedance stuff, but i guess they fed a capacitor bank to give high voltage low impedance working currents. I figured the 110 volt stuff was a poor compromise, but i see now that it is plenty high voltage. I have seen the same basic schematic for years and always figured it to be a toy.
                    Thinking about throwing a test EDM together, with an isolation transformer (home wound secondary, then if it really cuts, make a feedback loop to keep constant current.

                    Still wish I had numbers for upperlower frequencies used, any way thanks a million.

                    Andthanks Dave for more of theury of operation.

                    The thing that re-newed my interst was the village press picutres of the results of their latest EDM package.


                    • #11

                      I think the original project is a good one to tackle. The newer one has power for sure, but at what cost safety?


                      • #12
                        How about one those surplus Star Wars lazers from the 80s, I think they are in the megawatt range, they will vaporize any steel I have seen. :-)



                        • #13
                          Thrud: the voltages involved are near what any buzz box puts out (open circuit voltages). Problem with most of the simple EDMs is that you are playing with 110 volts and one side is 110 volts abouve ground and your body is at ground potential. A simple isolation transformer would make it so you could only be shocked by getting accross both leads at once, and the current path would be only from the places where you touched via your body. keep one hnd in your pocket, use a litle caution and its fairly safe. if the risks are acceptable, its safe enough for me. isolation transformers are cheap enough for anything that uses even two hundred watt lamps for currnet limiting. I re wound a microwave transformer years ago to amke me a true 100 amp battery charger for the Motorhome, all about 10 inches long and the width and hieght determined by the cooling fan. Too many folks worry about saftey when they do it themselves but trust the manufacturer to make them safe. Common sense and a little well placed fear makes things safe. you could make a good case of forbidding a lathe to the untrained- ten pounds of steel spinning at high RPMs, Razor sharp steel filings every where, sharp cutting tools, and if it comes unmounted could beat you severly about the head and shoulders. But its that "safe" grinder that gets skin and old clothes daily.