Eddie Tips: Drill Deep Holes Incredibly Straight

Eddie Bell explains how the “pecking” method keeps your drill centered and minimizes friction.

Last edited: 10/28/2019
Burlife assortment and a drill bit set

Rio Grande was founded in 1944 by my father, Saul Bell. A jeweler for more than 80 years, Saul was involved in every imaginable aspect of the jewelry industry, including manufacturing, diamond-setting, watch-making, wholesaling, and retailing. He loved to share his vast knowledge of the jewelry-making process. My brothers, sisters and I still benefit daily from his knowledge and wisdom, and I hope to pass on some of what I have learned from him and from other master jewelers through this series.

A few years ago, Charles Lewton-Brain showed me a slick trick for keeping drill chips away from the hole by making a little fan out of two pieces of tape attached to the drill bit. A narrow strip of tape is wrapped around the bit above the flutes, sticky side to sticky side, just a like a little propeller.

drillbits
Irwin Small High-Speed Steel Drills

This tip made me think about a trick I know for keeping really deep holes, very straight. I learned this trick from Jeff Zirwas, who is a fellow Rio Grande associate of many years and the best machinist and tool & die maker I've ever had the pleasure to work with. The trick is to interrupt the downward pressure just enough to let the drill bit stop cutting for a moment, then restart the cut in rapid little pecks, never taking the bit out of the hole until you're finished drilling. Peck drilling causes the cutting edge of the bit to bite at a different angle of rotation every time it starts cutting, which re-centers the drill bit and keeps it from being pulled to one side. Peck drilling also breaks the chips so that they are easily cleared from the drill. When the chip comes out in a long spiral, there is more friction in the hole, and both the work and the bit get hotter than would be the case if a lot of little chips were being made.

Of course, there are preconditions to drilling a straight hole, such as using a sharp, well-formed bit. Jewelers generally drill small holes, so their drill bits tend to be small and easily bent. If the bit isn't sharp, you must apply more pressure to make it cut, and that increases the danger of bending the bit, resulting in a ragged hole. If the bit is not sharpened perfectly on center, it will drill a bigger hole than the diameter of the bit. Lubrication is important for keeping the work and the bit cool, and it helps to keep the bit centered in the hole—lubricated chips clear the hole more easily, too. I'm in love with BurLife—I use it on anything that cuts or grinds because it reduces chatter better than anything else I've tried. You can sharpen drill bits, but for deep holes I always use a new one. Don't wait for a bit to get really blunt. Keep it sharp like your gravers, dress it often, and your job will be quicker. The old adage that a blunt cutting tool is dangerous is very true.

burlife
BurLife

I always use a center punch to mark the spot where the drill should center. I lay the punch on its side and align the point on the center spot. Holding the point to the work, I rotate the punch up and give it a tap. Then I bring the drill in contact just enough to show witness and look to be sure it is centered where I want the hole.

How deep you go before inspection for hole placement is important (once the bit point gets deep enough to encompass the full diameter of the drill bit, it can't be drifted to a new center point). If corrective action is needed, there is a trick to moving the drill bit to a new center point; however it only works if the drill impression is smaller than the diameter of the bit. Once the side of the bit is in a hole, side pressure will always break the bit. First, grind the bit so that it is as short as possible and chuck it so as little is exposed as is practical to still see your work. This works best in a drill press. The trick is to consider the rotation of the bit in picking the direction to push the work. If you want to move toward 12 o'clock (with clockwise rotation of the bit), move the work toward 9 o'clock and it will drift to 12. This takes a delicate touch and practice.

Remember, drill bits are brittle, hard and can shatter when they break. Any side load on a drill bit is definitely drill abuse and good eye protection is required. In fact, you should always protect your eyes during any kind of drilling.