Let Edming Use Sink In

Electrical discharge machining, or EDMing, is a form of machining wherein you use an electrode of some sort to channel enormous amounts of electricity into a workpiece to create your desired geometries. There are a few distinct types of electrical discharge machines (EDMs), such as small hole, wire and sinker. Their names imply the method by which the electrode delivers the electrical current.

A small hole EDM uses a small tube of brass to poke a small starter hole into your part, usually a starting hole for your wire EDM to feed its wire electrode through. Wire, as just stated, uses a tiny diameter wire (around 0.010″, sometimes coated) to travel the designated cutting path to give you the desired part. Wire is great for making dies and punches, as most machines currently available have four-axis capability in that the two heads of the machine move independent of one another to allow for things like die draft angles.

You also have the option of a sinker EDM, of which I am focusing on here.

Sinker EDMing

This method of EDMing uses a pre-determined shape of electrode (most made of high-density graphite or copper-tungsten). So long as you can machine the negative geometry of your desired feature and attach it to the toolholder for the machine, you are in business. (See figure 1 for a test part made before burning the shape into a mold body.)

Sinker EDMing is an easy decision for any shop that deals with hard machining or that needs to work with heat-treated parts. So long as the part can conduct electricity, the sinker EDM can do the job.

Sinker EDMing is also a standout option when you need to cut complex geometries or perfectly square-cornered pockets into your parts. See figure 2 for an example of a part my students and I made using our sinker EDM. It has a 7/16″ hex straight through the part — for a mating locking lug.