Deep hole drilling that’s “just right”

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by Kip Hanson

Goldilocks and the quote for Three Bears


Gabriella Goldilocks had a problem. Her father’s machine shop, G&G Machine, had just received a big drawing package from Three Bears Petroleum Products Inc. in Edmonton, AB. It was a family of components for the new multiport flow selector they were working on. Gabriella did some quick calculations and knew the order would be worth several million dollars, enough work to keep the small shop busy for months.

She examined the first drawing, a small throttle body made of high-strength steel. Her crew would have no problem machining most of it, but those 1/8 in. (3.18 mm) holes through the long axis of the part would make or break the deal. Gun drilling was out—those guys over at Big Wolf Precision would eat up every bit of profit. She needed a better way to drill those holes.

A Google search returned entirely too many options—it seemed every tooling company on the planet had some sort of deep hole drilling solution, and they all said theirs was best. “Always grab the bull by the horns, girl,” came the voice of her father. Gabriella picked up the phone and did just that, calling Kennametal’s regional product manager for Holemaking, Steve Pilger.

Steve was very helpful and after Gabriella explained her problem he suggested she make use of Kennametal’s new manufacturing advisor software, called NOVO. “This is quite a huge project you need to find solutions for. For such complex tasks I would propose to try our NOVO system to get an initial understanding between which manufacturing possibilities you can choose.”

Gabriella was all for software solutions but she didn’t have time right then to download it. She interrupted him. “Not now, Steve. Just find me an 1/8 in. (3.18 mm) drill that can go nearly 4 in. (102 mm) deep in A36 steel.”

Steve steered her towards Kennametal’s line of B27_HPG solid carbide deep hole drills, which according to Steve, remove metal 3-4 times faster than gun drills or high speed steel, in depths up to 30 X diameter.

Gabriella pushed. “Everyone makes deep hole drills, Steve. What’s so special about yours?”

The answer was simple. Aside from the tool’s 4-margin flute design, Kennametal now offered the entire series in a new grade of carbide, KCPK20, which together with a proprietary ALCrN coating, offers excellent wear resistance in uninterrupted cuts, just right for hydraulic blocks, cylinder heads and fuel injection components. “But that’s not the whole story, Gabby.”

Steve continued with some application device. Unlike many drills, the B27_HPG drills handle crossholes and inclined entries or exits. High coolant pressure is recommended—the greater the coolant volume and pressure, the better the chip evacuation in any drilling application, although Steve pointed out that the B27_HPG requires far less in the way of coolant flow than do comparable drills, due to the highly polished flutes. And he advised drilling a short pilot hole. “Use a KMT Unidrill of the same size, but one with a wider point angle. This prevents drill walk.”

“Thank you, Steve. Your deep hole drilling solution sounds perfect.”

Machining medium holes
Gabriella Goldilocks tackled the medium-sized holes next. She called Derek Divok, technical specialist for Komet of Canada, Newmarket, ON. “Derek, I need some help.” She explained the problem—a series of 1-1/4 in. (31.75 mm) holes nearly 7 in. (178 mm) deep in a 316 stainless steel manifold block, all of which intersect a large bore in the center of the part. Gabby knew from past experience that break-through would chip the outer margins on most drills, driving her tooling costs through the roof.

“Sounds tough,” Derek said. “But I think we can help.” He outlined his solution: Komet’s Centron series drill. “It uses an ABS mount, and has carbide guide pads on the periphery of the drilling head. These support the drill when you break into a cross hole. And it’s modular—you can use the same drill body for a range of hole sizes.” Derek encouraged her to check out the application examples on the company website, but offered one closer to home. “We have a customer outside of Calgary that makes fracking equipment. They drill similar sized holes, around 40 mm x 300 mm deep in 4340 steel, and run 2500 rpm at a feedrate of 250 mm/minute. They tell me they doubled their output over previous drilling methods.”

“What’s the catch, Derek?” Gabriella Goldilocks wasn’t born yesterday.

“You’re going to need around 14 kW of power at the spindle, and plenty of Z axis torque. Do you have a machine that can support that, Gabby?”

She did the math, and knew her 40-taper VMC probably wouldn’t cut it. “That’s fine. We’ll put it on the big Okuma. It has 20 hp.”

“One other thing,” warned Derek. “Make sure you drop the feedrate when the drill breaks through. Cut it in half, or you might break the tool.”

“Thanks, Derek. I’ll get back to you.”

Drilling large holes
Gabriella had one more call to make, for the toughest hole of all: how in the world was she going to drill a 4 in. (102 mm) diameter hole over 6 ft (2 m) deep in 4100-series steel? Surfing the Iscar website, Gabby saw a glimmer of hope. She picked up the phone.

“David Vetrecin speaking.”

As product manager for holemaking at Iscar Tools Canada, Oakville, ON, David should have some answers for her. She described the workpiece and crossed her fingers.

“You need an ejector,” he told her.

“Huh?” At that moment, Gabby wished more than ever that her father was there.

David explained the system. Ejector drills, also known as double-tube, or DTS systems, use a “tube within a tube” approach. The drill head screws onto the outer tube, and is guided by a starter hole or special bushing mounted near the face of the workpiece. Cutting fluid is forced between the two tubes and down around the drill head. This lubricates the head and carries chips back through the inner tube. “These things drill like crazy,” he summarized. “And there’s virtually no limit to the hole depth.”

“Sounds complicated. I thought systems like this need a special machine.”

“You’re thinking of single-tube, or STS systems,” countered David. “Do you have an engine lathe?”

Gabriella thought about the old Lodge and Shipley her dad bought at auction. The thing had been sitting in the corner of the shop collecting dust ever since. “Yeah, maybe. What do you have in mind?”

“Most people retrofit an existing machine for an ejector drill. And you’re going to need a high volume coolant pump—100 gpm or so—along with some bushings and sleeves, coolant inducer, drill collets and so on. It’s no big deal, Gabby, really.”

“What kind of tolerances can you hold?”

David hesitated. “It kind of depends on the machine setup. If everything is rigid, and you have a good fit on the drill bushing, you can probably hold an IT10 or better—figure +/-.005 in. (0.13 mm) worst case, with a 60 Ra finish.”

“Wow. Anything I need to worry about?”

“You should probably use a straight oil,” David said. “Water soluble doesn’t work so great.”

Gabriella thought about it. An efficient way to drill that monstrous hole would almost certainly win the quote for her. “You sure this thing’s going to work, David? I have a lot riding on this.”

David laughed. “Don’t worry about it, Gabby. It’ll work.”

Goldilocks hung up the phone and smiled; her email was filling up with quotes for drilling systems. The tooling people had really come through for her—three drilling solutions, each of them just right for her application. She plugged in the tooling costs, added a comfortable safety factor, and then sent the quote off to Three Bears.

Early the next week, she got a call from Tom Woodcutter, head buyer at Three Bears. “Well, you weren’t the cheapest, Goldie, but we trust you to get the job done.”

“That’s great, Tom. Thanks.” Boy, this was really going to help the bottom line.

“There’s just one catch, though,” said the buyer with a grin. “We need the prototypes in four weeks.”

Gabby hung up the phone and called her shop foreman. “Looks like we’ll be working some overtime. Get up here.” SMT

Kip Hanson is a contributing editor. [email protected]

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