A pricey solution pays off with saved time: expense-like beauty-is in the eye of the beholder. What may seem like a big up-front investment can provide a big pay-off.

One of our repeat jobs is a 4140 steel shaft, with a hardness of 28 to 32 Rc. One hole in the center of the piece is 0.421" in diameter and nearly 12" deep. We've tried different methods to get this length-to-diameter ratio. We've tried drilling as deep as we could with carbide, and doing the rest with an extra-long high-speed steel drill, but this wasn't a viable solution.

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In the range of 30xD, coating, tip grind, and coolant options are limited to a generic high-speed steel drill. In this steel, we had to peck every 0.05" to keep the chips small to prevent them from bunching up in the drill. It took about 35 minutes to drill this single hole.

"It's slow, it's hard on the machine, and it's old fashioned," my father said. "Find a better way."

Readers may recall a tooling test where we broke a drill after second-guessing our feeds and speeds after some successful holes. We finished that order with high-speed steel. I had one last chance to redeem myself with the next batch. I was confident enough using Titex drills on a different projects to try them on this one. I had drilled holes of up to 20xD with little trouble. I found the drill I needed in the Titex catalog: 11mm in diameter. At 30xD, its drilling depth was a max of about 12.5". I needed a depth of only 11.7".

Sticker Shock

The drill wasn't cheap at $750. It also required a pilot drill-at $150-designed to start the long drill in a clean hole, for a pricey $900 total.

It would save a ton of time and would pay for itself during the 72-piece run-if it didn't disintegrate.

My local Titex representative said the company would guarantee the drill on a test basis. With his help, and the procedure sheet, we calculated feeds and speeds.

I mounted the drill into a new collet, using a sealing disc for optimum coolant pressure through the drill. I checked the tool run-out on the tool pre-setter and made sure it was true.

First, I drilled using the pilot drill. The sheet recommended 1.5xD, but I ended up with a little less, because of another feature in the part. This provided a cylindrical entry point for the drill. The point of the pilot was designed to ease the longer drill into the cut.

With the pilot finished it was time to drill. I wrote a deep-drilling program. The first step was to enter the pilot hole at 25 percent of the final spindle speed, at 1 ipm. To keep the drill from wobbling, the speed didn't exceed 500 rpm to prevent run-out problems.

Once into the pilot I turned on the coolant. I fed to 3xD deep at the advised 25 percent of spindle speed and 25 percent of chip-load. This produced long chips, but since it was close to the end of the hole, they easily evacuated.

I added one-second of dwell to clear the bottom before increasing spindle speed to 100 percent of the recommended value. I allowed one-second of dwell after the speed change to ensure it was up to speed.

No More Pecking

I then fed to depth at recommended speeds and feeds all the way to the bottom of the hole, no peck required. Or, at least that was the plan.

Within about 2" from the end depth, the drill's light squeak became louder. I decided to stop and investigate before any potential disaster.

I found the first 4" of flute were packed with chips. Besides the chips that were not finely ground, I found some were not as completely broken as they should be. I would need to feed faster.

I double-checked the feed recommendations and went from 0.005" inches per revolution to 0.006". At a spindle speed of 1,300 rpm it changed the feed from 6.5 ipm to 7.8 ipm. I re-entered the hole and drilled the rest of the way. There was a little more squealing and more packed chips, and smaller-but still unbroken-chips in the flutes.

I increased our feed-rate. After checking with the Titex representative-technically it was still his drill-I increased the chip-load to 0.007" ipr. On the next piece, it barely made a sound as it cruised to 12" at 9.1 ipm, a bit more than 80 seconds. Even with the extra pilot drilling, and slower entry procedures, this shaved cycle time about 29 minutes. Thirty pieces later the drill was going strong. We haven't used high-speed steel drills since.

Dave is responsible for programming, tool selection, and fixture design for Ansco Machine's 20 CNC machines in Peninsula, Ohio. He's been working in a machine shop since age 12, starting by drilling holes on a turret lathe and making simple parts on a Bridgeport.