Small Hole EDM

The most common electrodes for Small Hole EDM are made from Brass or Copper with one or more through ports for flushing that go down the ID of the electrode – providing cooling directly at the point of machining. Brass and Copper electrodes are the most cost effective, burn the most efficiently and work well when drilling tool steels and stainless steels. Other less common drilling electrodes are made from Copper Tungsten, Molybdenum, Tungsten Carbide, and Graphite. Xact Wire EDM uses Brass and Copper primarily. Disadvantages of the exotic material electrodes are cost and fragility. [Drilling Speed is mainly dependent on the material being EDM drilled]

Single Channels are essentially pipe electrodes and can be used for high-speed applications. However, if the electrode OD is > .035” diameter, there can be a remnant of material not EDM’d in the center of the hole which can cause burning issues or depth control issues. Single Channel electrodes work well when the OD is less than .035” diameter in our experience. Either Water or Oil Coolant for flushing of the EDM’d particles is essential. [Multi-channel (2 or more) ID ports for flushing within the electrode will aid in removing the full amount of material when drilling holes]

There are no finishing/skimming settings for Small Hole EDM. One pass through and the machining is complete. The finish of the drilled hole depends on many factors. If a better surface finish is required for the ID of a small hole, Xact Wire EDM will EDM drill a smaller hole with Small Hole EDM, then use Wire EDM to polish open the hole to size spec. After finishing the hole with wire EDM, the surface finish can be as good as 16 micro inch RMS and accurate to within .0002” when necessary.

Small Hole EDM is ideal for holes with an angle of entry that is not perpendicular to the top surface. Standard drill bits will struggle to enter the material in the proper location due to deflection as the standard drill point will not be the first to contact the entry surface. The entire face of an EDM drill electrode is always machining and will enter at the location it contacts. The steepest angle of entry that Xact Wire EDM has experienced is 80 degrees from perpendicular with repeatable location results. Huge advantage!

Yes. Small Hole EDM is excellent for drilling blind holes of less than 3mm in diameter. Due to the finish at the bottom of the drilled hole, a typical tolerance for depth is +/-.025”. Depth control is also important when a Small Hole EDM machine is used to break apart broken drill bits, broken end mills, broken screws, or broken bolts.

Small Hole EDM can be used to drill small holes in any conductive material. Stainless Steel and Tool Steel are EDM drilled most efficiently and with the least number of issues. Carbide will EDM the slowest due to its density and high melting point temperature. An EDM drilling machine with oil-based coolant is the best approach when adding holes to carbide and tungsten workpieces. Xact has both oil-based and water-based machines. [Electrode diameters of .040” to .055” provide the fastest drilling speeds and straightest holes in typical workpieces and materials]

Drilling deep holes with Small Hole EDM can be challenging. The deeper the hole requirement, the farther the small electrode is drilling away from its guide, and the electrode can occasionally ‘walk’ from its axial position by about .001” per inch. The larger diameter electrode that can be used, the less likely it is to ‘walk’ from its precision location. For more precision Small Hole locations, Xact Wire EDM can usually drill the small holes from both sides of a workpiece and maintain accuracy. Once a depth meets or exceeds 4” depth, the best approach is to have the electrode enter from each end of the part and meet to create a through hole.

[The tallest workpiece that Xact Wire EDM has EDM drilled is 14” thick entering on location from both ends and with drilled points meeting in the middle successfully]

Yes. Small Hole EDM is a strong process for drilling intersecting holes or drilling through multiple cavities, as there is zero threat of a “broken drill bit” which could potentially scrap any workpiece.

Xact Wire EDM drills holes using electrodes as small as .010” diameter, and as large as .210” diameter electrodes. Electrode diameters of .040” to .055” provide the fastest drilling speeds and the straightest holes in typical workpieces and materials.

Yes. Parts or raw material can be stacked and EDM drilled efficiently. For the optimum drilling speeds, it is best to be able to stack as tightly and flat against each other as possible. This will also minimize the amount of EDM’d particles getting between each layer.

De-ionized and filtered water is the most common coolant used in a Small Hole EDM machine. Some Small Hole EDM machines used to drill holes in carbide have an oil-based coolant or solution. Coolant is critical to flush away the EDM particles being machined away at the point of erosion. Coolant needs to be flowing through the ID of the electrode for optimum machining performance. Coolant can also be delivered by an auxiliary hose at the point of entry to flush particles away from the work area. At Xact we also have machines that allow the workpiece to be submerged in coolant during the drilling process.

Small Hole EDM’d holes are accurately located within .000”-.005” of location from a precision pick up hole or Datum corner. Due to the EDM wear on the electrode tip the hole diameters can be held as tight as +/-.0025” when checked with gage pins. If a tighter tolerance hole is required, Xact would add a Wire EDM operation to dial in precision size, location, straightness, and surface finish of the hole.

To achieve the best results with a Small Hole EDM machine and electrode, Xact follows the 1:100 electrode diameter to depth guideline. Example: A .040” diameter electrode performs best up to 4.00” depth.

Small Hole EDM is an excellent method of machining small holes for various applications:

• Drilling small holes in Hardened or Heat-Treated materials
• Drilling small holes in very soft, gummy, or exotic materials
• Drilling start holes in components for subsequent operations in a Wire EDM machine
• Drilling coolant or air holes in end mills, taps, and cutting tools for optimum coolant at the point of cutting
• Drilling Safety Wire Holes in Aerospace applications [high angle of entry]
• Drilling clearance holes for wires and deep holes for thermocouple applications
• Removing broken drill bits, end mills, screws, and bolts to keep a component or tool from being unusable or scrap.

The most cost-effective electrodes for Small Hole EDM are Brass and Copper. The most expensive electrodes are Molybdenum and Tungsten Carbide. Long electrodes are essential in the process due to the electrode wear during drilling as well as factoring in the depth of the hole to be drilled. [There is often approximately 6”- 8” of electrode remaining as scrap once the machine reaches its maximum depth]

The life expectancy of a single electrode will vary based on the thickness of the material it is drilling. At times a single electrode can machine up to 50 holes before wearing down. At other times, a single electrode will only last long enough to drill 50% of the depth of a long deep hole. At that point, another new electrode will need to be installed to finish drilling through the workpiece.

Yes. Xact Wire EDM utilizes automatic electrode changers for efficiency with electrode changes when running fixtures with multiple components in the machine at once, or when several holes are required in a single workpiece. With the automatic electrode changer being utilized, the machine can run unattended for many hours without operator interaction.

Small diameter electrodes (<.020” diameter) can present some interesting challenges. Handling the electrodes is delicate, as any crease or bend will render the electrode unusable. Secondly, as the small electrode extends further from the guide, there can be tendency for the electrode to lose some of its power or energy for machining effectively. Lastly, coolant should always be flowing through the ID of the electrode for optimum drilling speed. Smaller electrodes can warp or bend, or can have the ID plug – which keeps coolant from flowing. This immediately shuts down the drilling process.

The best methods that Xact Wire EDM has found for inspection of Small Hole EDM work are the use of precision gage pins and a Vision Inspection System.