The IDCT microdrilling mechanism is a unique alternative to a traditional drill spindle. While most of the industry has focused on developing small incremental improvements in the air bearing spindle design, the mechanism was designed from scratch as a completely new alternative. The high RPM and zero runout of this mechanism make it ideal for drilling holes in the .018" to .002" diameter range, and high aspect holes are unmatched by any other mechanical drilling device. At the same time, this unit is capable of drilling holes up to .125" diameter, routing larger holes, and doing fineline routing in most materials. It uses standard .125" shank drills and requires no ring setting. Speed, accuracy and flexibility are all available in one unit. The mechanism does everything the other mechanical drillers can and more, truly filling the gap between mechanical and laser drilling.

Mechanical and air bearing spindles have certain inherent disadvantages. One is that they use the motor core to turn the drill. This means that the motor core must turn at the same RPM as the desired drill speed. Mechanical bearings lose their effectiveness at relatively low speeds. Air bearings allow much higher speeds, but still have limitations. Motor cores are heavy, resulting in having to strike a balance between ideal speed and the tendency for the large mass to become unstable or come apart at high speeds. A solution to this is to reduce the mass and diameter of the motor core, essentially miniaturizing the standard air bearing design. As the mass and diameter reduce, however, so does the effective torque. This reduces the ability to drive larger diameter drills, often resulting in stalling or a complete inability to drill larger holes when required. Some manufacturers have gone so far as to provide special, reduced diameter drill bits which are non-standard to the rest of the industry. Air bearings also require cooling. The very air cushion which provides the low friction bearing surface is also an excellent insulator. Heat generated by the motor core is insulated from the surrounding material, which might otherwise conduct it away. Water cooling systems are often used to assist in heat dissipation, creating bulky connections and heat exchanger maintenance.

Collet style spindles have an additional disadvantage in that they actually create axial runout. Holding true concentricity across the entire group of individual pieces in this type of mechanism is impossible. While runout can be tolerated to some extent when drilling larger holes, small hole drilling is extremely sensitive to runout. Axial runout causes overheating, poor hole quality, breakage, and short drill life. Radial runout, or "whipping", causes breakage both in and out of the material, as well as drill wander when drilling high aspect holes. Many collet based spindles required ringed drill bits. Besides the nuisance of setting, moving or removing rings, the rings add their own imbalances to the system at high speeds.

The IDCT microdrilling mechanism is a very simple system conceptually. Standard production mechanisms run 275,000 RPM with ease. Particularly well-tuned units have been run in excess of 320,000 RPM for extended periods and development continues to push new boundaries. The secret to this is that the only component in the system which turns at these speeds is the drill bit itself.

The primary mechanics of the system consist of three high precision, hardened tool steel wheels arranged in a triangle fashion. Two of these wheels are mechanically driven, while the third wheel is an idler. The drill rides against the faces of the two drive wheels and is held against them by the idler wheel (See Figure 1).

FIGURE 1

The high RPM is accomplished by way of a simple mechanical gear-up, using the faces of the wheels and pulleys in the system. Note the large diameter of the drive wheels relative to the small diameter of the drill shank. Every revolution of the drive wheel produces multiple rotations of the drill. Turning the wheels at approximately 45,000 RPM produces a rotation of the drill at 275,000 RPM. Traditional air bearing spindles are just now reaching speeds of 170,000 RPM, yet this is well below the ideal speeds (and feeds) for any drills under .018" diameter. Ideal RPM requirements in these diameter ranges begin an exponential rise at almost the same point that air bearing spindles just can’t give any more.

The drill stroke in the IDCT microdrilling mechanism is accomplished using the same wheels that provide rotational drive. A highly sophisticated servo control loop introduces tiny amounts of skew in the wheels, creating either up or down force vectors on the drill shank as it rotates. A simple way to visualize this is to hold a pencil (drill) in a vertical position. Now place a soda can (drive wheel) alongside of it in the same orientation so the side of the pencil and the side of the can are in full contact. You can see that one revolution of the soda can would turn the pencil around many times. Keeping the pencil vertical and the side of the can against it, tilt the top of the can a few degrees away from you. If you visualize the can as a turning wheel, you can see that it not only spins the drill, but simultaneously introduces a force along the vertical axis of the drill. This creates a virtual thread on the drill shank, spinning it and causing it to move down at the same time. At high RPM, this can produce feed rates of as much as 800 inches per minute with a few tenths of a degree of wheel skew. Slower RPM, slower feed. Faster RPM, faster feed. More wheel cant, more feed. Less wheel cant, less feed. Higher speed means higher feed, removing more material in less time. Less time in the hole translates to faster production, less wear and tear on the drill, and less heat build up in the drill or the work piece.

Runout in the IDCT microdrilling mechanism system is virtually un-measurable. The wheel mechanism controls both rotation and drill stroke. There is no build up of concentricity problems in the assembly. The drive wheels are matched to within .0001" and are precision aligned at assembly. No axial runout, no whipping. This results in less breakage, less drill wander in high aspect drilling and less stress and heat build up due to side loading and friction. Perhaps the largest benefit, though, is in the significant extension of useful drill life. .006" diameter drills still produce excellent holes after 6,000 holes, .008" diameter up to 8,000 holes and .010" diameter up to 10,000 or more holes in FR4 with four copper layers. Most shops would throw away a .006" drill after 1000-1500 holes.

Faster material removal and fewer tool changes routinely result in significant reductions in job run times, using less than one third the number of drills to do the same job.

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