Tips for Choosing the Right EDM Drill Tube

Mark Cicchetti, Absolute Machine Tools’ EDM Technical Director, was recently asked by EDM Today magazine to offer advice on choosing the right EDM drill tube for different applications.

Find out Mark’s thoughts on this topic below!

Choosing the Right EDM Drill Tube

When choosing the right EDM drill tube, there are several different configurations and materials available. The basic materials are copper and brass. These make up 95% or more of the tube sales. Copper tubes work best in carbide, with brass for steel and almost anything else.

The other significant option relates to the number of channels through the tube used for flushing.  The most common are single, double and triple channel. The information offered here will be most relevant for the typical size range of 0.3mm to 3.0mm diameter applications.

Single channel tubes typically burn faster than any other type because they machine less material than multi-channel tubes, except for a big problem that can be summed up in one word: stalagmite.

The Google dictionary definition for stalagmite is “a mound or tapering column rising from the floor of a cave, formed of calcium salts deposited by dripping water and often uniting with a stalactite.”

That definition is good, except for with EDM applications, the stalagmites are not formed by dripping water over a long period of time and there is never a stalactite associated with it. In EDM machining, stalagmite is formed in seconds by the material left behind from the rotating electrode with a single hole right on the center.

The overburn from the spark gap is not large enough to erode away the center material in electrodes larger than just 1mm in diameter. These stalagmites when drilling deeper holes grow up into the center of the electrode, eventually breaking off and causing shorting and inconsistent drilling. It will be flying along, then suddenly just start sputtering and backing up.

That’s why multi-channel tubes were made. The rotating electrode with multiple offset channels erode all the material in the hole, making it possible to do deep hole drilling without shorting or backing up.

Here are the basic applications:

• Single channel tubes: 0.7mm diameter or for through holes in materials less than 10mm in thickness. Never use a single channel tube in blind holes; those stalagmites will get you every time.
• Double channel or “I Bar” or “Double D” tubes: These can have mixed results based on the manufacturing method of the tubes. In many cases, the tubes are made by drawing a round tube around a rectangular bar. Mark noted that he’s actually seen the center bar separate from the tube in deeper holes.
• Three channel tubes: When possible, the three channel precision extruded tubes offer the most consistent results in most common applications. The limitations for availability of these tubes are primarily based on the outside diameter of the tube. It is hard enough getting a hole in the center of a 0.1mm tube, let alone multiple tubes.

Get Help With All Your EDM Drilling Needs

Find out more about EDM machines and get help choosing the right EDM drill tube for your needs by emailing Absolute Machine Tools today at sales@absolutemachine.com.