As I mentioned in the previous post about taping the oil galleys with pipe plugs brought up an interesting experience from my past.
As I mentioned AR started hardening their crankshafts with the 2 liter Nord engines. Even after 100,000 miles rarely would you see a crankshaft that needed to be turned. That is unless the owner of said engine treated it badly by not changing the oil often.
I had an Alfetta at the time, and the crank plugs fell out. Even after installing new plugs, the plugs fell out again. I pulled the engine, and removed the crank. Putting the crank in a suitable fixture to hold it, I started to tap the oil galley holes for the pipe plugs.
The tap only needed to go in about 3 full turns (est) to get the plug in far enough to be flush. Most of the holes went along just fine, then I had one that I was turning and the tap just snapped off flush with the crank. Being that the tap has cutting threads you can’t just leave it there as the oil would flow out through that hole. Knowing that the tap was super hard, removing it would prove futile. It was then I called a local machine shop that turned my crankshafts and asked them what to do. They said to take it a firm in Los Angeles called TapEx. They have an EDM machines.
I headed off to Los Angeles about an hour drive away to the company called TapEx. They have several EDM machines that remove problems like mine.
Here is a quick primer. Ever go to the movie theater before the 1990s? There was a guy in the projection booth that ran a carbon arc projector. They were also used for search lights in the war and afterwards for advertising. Those carbon arc projectors used a carbon rod electrode and high voltage to create a flame as bright as the sun. They used a positive and a negative carbon rod that moved slowly to keep the flame burning.
So, now you asking yourself, what in the heck is a EDM machine. Hey! I am glad you asked. For starters the machine is an Electrical Discharge Machine. The part is submerged in a non conductive fluid and a penetrating probe is inserted into the hole to remove the metal. There are 3 kinds of machines used in the EDM process: wire EDM, hole EDM and Sinker EDM. Using a spark at 100,000 times a second with the metal being melted or vaporized the metal is removed with the help of the fluid. The fluid also keeps the metal from being distorted. The electrode and the metal to be removed is never touched so as to create an arc. The gap is as small as the diameter of a hair. One part is negative and the other is positive which creates the spark or flame.
A tap extractor is known by many names including an EDM machine, tap burner, metal disintegrator, and spark eroder. These metal disintegration machines are used to remove broken bolts, taps, and drills without doing any damage to the surrounding part. Cheap systems often make the situation worse or are not even necessary. With an electric discharge machine (EDM) you get the precision, speed, and value without the cost of replacing parts on expensive equipment.
So, why use an EDM machine? Here is from a source I copied from*:
The main advantage of electrical discharge machining is that it can be used on any material as long as it is conductive. It is therefore possible to machine workpieces made from tungsten carbide or titanium that are hard to machine with traditional cutting methods. Another advantage of electrical discharge machining is the lack of mechanical force put into the workpiece. Fragile outlines are easier to produce because there is no high cutting force needed to remove the material.
EDM also allows for shapes and depths that are impossible to reach with a cutting tool. Especially deep processing where the tool length to diameter ration would be very high, is a usual application for EDM. Sharp internal corners, deep ribs and narrow slots are other specialities of electrical discharge machining. Another argument for using EDM is that the surface finish is usually better than with traditional methods. Electrical discharge machining produces surfaces with a fine finish and high precision.
A Sinker EDM is used to create parts by burning away the metal that are made from carbon or copper. This is the negative side of the electrode and used to create complex shapes.
The Wire EDM uses the principle as the carbon arc projector using a wire feed to create the arc. The wire EDM can cut a hole down through the metal. The wire is usually copper or brass using de-ionized water and with the wire held in place by diamond tips.
The last is the Hole EDM, which actually makes holes in parts using a round tip with holes for pushing water through next to the arc.
This is a slow process that can take up to several hours depending upon the part to be removed.
As it turns out I had to leave the crank there for several days and then do a turn around to go get the part. My wallet was a lot lighter, the hole was perfectly clean and ready for a new special hardened tap to finish the job.
The places that have an EDM machine do a fair amount of work for people and companies and rescue guys like me.
Want to see how they work, go to YouTube and look up EDM machines.