Deep holes are among the most costly kinds of machining jobs done in contract machine shops. However, many shops are now offering less expensive techniques. It pays to seek out such vendors when work involves deep holes on machined parts.

It used to be that when you mentioned deep holes to metalworking contract shops, eyes rolled and calculators hummed. Big numbers popped up after dollar signs.

Not that vendors were trying to make a killing. Rather they were protecting against the common risks of machining deep holes in metal workpieces with twist or gun drills. Slow pace of production, broken tools and rejected parts all weighed on their minds.

Things have changed-at least in the many contract shops using an alternative proven method for deep-hole drilling. Called Ejector Drilling, the method boosts metal-removal speed by a factor of 5 to 20. It also minimizes tool breakage and results in straighter, rounder, dimensionally more accurate holes.

The bottom line for the buyer is a share of the savings realized by shops using ejector drilling. How much savings? We estimate the method could easily cut costs by $80 to $100 million per year nationally. This figure covers holes larger than 3/4" diameter with depth/diameter ratios greater than 5:1.

Bringing it down to an individual level, one user saved $18 per weight reduction hole in the axles of military vehicles. The previous method--gun drilling--took 45 to 60 minutes per hole while Ejector Drilling takes only five minutes.

Ejector drilling presents multi-bit cemented carbide to the drilling face and sucks chips out through the center of a hollow drill tube. This internal chip evacuation eliminates all the problems of clearing chips via the flutes of a solid-section twist drill or the clearance segment in a gun drill shaft.

As a result, chips that go up to the middle can't jam between drill and hole surface-so it's goodbye to the Hobson's choice of go slow or break tools. Farewell, too, to "pecking" drill a little, pull tool to clear chips...drill a little more, pull tool again. And chips that aren't there can't hurt the hole surface-so look for 60 micro finishes.

Not all contract metalworking shops offer ejector drilling. Because the equipment requires a five-figure investment, vendors must consider the method a capital purchase, rather than a supplies or consumables buy. Those who have made the commitment have seen their investment paid back by savings in an average of six months. Sharing the savings with customers clearly gives them a competitive edge-and makes them worth shopping for when there's deep-hole work to be done.

The 200-plus contract and captive metalworking shops currently using ejector drilling have a broad range of applications in the automotive, defense, chemical process, oil patch, hydraulics and machinery fields. The savings they enjoy depends, of course, on the method they switched from, and on the depth/diameter ratio of the holes on specific jobs.

Ejector drilling is not the answer to all needs. First, it is not available for hole diameters below 3/4". Second, it is suited only for machineable materials that generate easy-to-control chips. That eliminates most nickel-based and many non-ferrous metals.

However, a sister method--the Single Tube System, or STS--can do holes as small as 1/2" diameter. STS also accommodates materials with poor chip-formation properties such as stainless steel and low-carbon steel. In the U.S., STS is at work on holes from 5" to 40" long and up to 12" diameter. Ejector drilling does holes from 5" to 5', up to 6' diameter.

Ejector drilling and STS differ principally in how drilling fluid gets to the cutting surface. An ejector drill shaft is a tube within a tube; drilling fluid moves down the annulus between the tubes. Not the angled slots in the inner tube. These allow about 30 percent of the pressurized oil to flow back up the tube, thus creating an aspirator-type vacuum to facilitate chip and return oil flow.

The proven savings potential in ejector drilling and STS suggest very strongly that buyers of deep-hole work take two steps before settling for twist or gun drilling. One is to analyze all deep-hole work to evaluate the savings possible with a 5 to 20 times increase in drilling speed. The other is to shop around for a machining operation that has made the commitment to these high-speed, high accuracy systems.