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Drilling a 0.067″ diameter × 2.7″-deep hole at a 4° entry angle

Drilling a hole with depth-to-diameter ratio of 40:1 at an angled entry is a challenging callout for many CNC machining platforms. However, as part of an R&D effort for a customer, we recently produced such a feature on our Hurco VMX42i mill.

High aspect ratio drilling at this scale — 0.067″ diameter, 2.7″ depth — may have been achievable on our Swiss CNC lathes. However, the 4° angled entry requirement compounded the difficulty of the feature and placed it outside the limitations of our current CNC turning centers.

This led our team to the development of a process for angled, deep hole drilling on a standard 3-axis vertical machining center (VMC).

This technical note describes the process development steps we used to machine this challenging deep hole drilling feature on a standard VMC.

Primary Machining Risks

Developing a process for drilling a 40:1 hole at a 4° angle required us to first assess the primary failure risks associated with the operation:

• Chip packing and tool breakage: without high-pressure through-coolant, chips cannot be flushed continuously. Chips that accumulate in the bore can pack against the drill, causing it to deflect or snap.
• Drill wander: a 0.067-inch drill running 2.7 inches deep has very little inherent rigidity. Lateral force from an off-center entry, chip interference, or resonance in the cut deflects the tool off-axis, producing a hole outside positional tolerance.
• Work Hardening: The material we used in our test coupon was 17-4 PH Stainless Steel — a hard, work-hardening alloy that would test the tooling under heavy stress. A peck and retraction cycle can exacerbate work-hardening conditions.

Our process design was structured to address each failure mode explicitly.

Process Design

Tooling

We selected a Nachi 40xD drill based on tooling supplier recommendations for this diameter and depth range.

Toolholding

A hydraulic chuck was specified to minimize spindle runout. At 40 times diameter, concentricity error that would be negligible in a standard drilling operation compounds significantly at this depth ratio — the hydraulic chuck reduced this as a variable.

Entry Sequence

The angled entry surface introduces an asymmetric cutting condition at drill engagement. Our process addressed this with a two-step preparation sequence before the 40xD drill entered the cut:

• Spot drilling: A spot drill established an accurate starting geometry on the angled surface, preventing lateral drift during initial engagement.
• Piloting: A pilot drill opened a centered, full-diameter entry hole before the 40xD drill advanced. The pilot hole constrained the deep hole drill at the entry point — centering the drill.

Peck Cycle

Our process managed chips mechanically through controlled peck cycles rather than coolant flush. The tooling supplier’s guidance bracketed initial peck depth increments at 0.5 to 1.0 times diameter, which translated to roughly 40 to 80 peck cycles per hole. This increment was designed to break chips before accumulation reached a level that risked packing or tool breakage.

Retraction Strategy

Between pecks, we retracted the drill so that it remained within the pilot hole — not fully above the part face. Full extraction would allow the spinning shank to whip laterally while unsupported, introducing a destabilization risk at re-entry. Keeping the drill guided within the pilot hole throughout the peck cycle maintained consistent re-entry geometry.

Coolant

Standard VMC flood coolant at 300 PSI. Chip evacuation relied on the peck cycle rather than coolant flush. Investment in higher-pressure through-coolant delivery remains an option for future process refinement.

Results

Through optimization of speeds, feeds, and peck depth, we achieved a cycle of approximately 80 seconds per hole. Optical comparator measurements of the hole locations allowed us to report tolerance thresholds we could reliably achieve. Tool life did not reach its limit within the R&D cycle but exceeded 200 holes without breakage.

Key Takeaways

While dedicated deep hole drilling equipment is purpose-built for challenging features such as 40xD angled holes, a well-designed VMC process may be serviceable — particularly where small batch volumes do not justify capital investment in specialized equipment or an additional supply chain leg. This R&D effort confirms that with deliberate process design, a standard 3-axis VMC can produce a 40:1 depth-to-diameter hole in 17-4 PH stainless at a 4° angled entry and sustain tool life past 200 cycles. Therefore, a 40xD feature on a print is not automatically a reason to decline, subcontract, or invest in new equipment. It is a reason to ask whether a well-designed process on existing equipment can meet the specification.

What starts with stock and finishes as a testament to precision? Andrew Bogart’s CNC machining — and dirt track racing.

Andrew, a CNC machinist at Micron, has been racing since 2015, starting with go-karts and working his way up to stock cars. This season, he’s making the jump from Street Stock to Pro Stock — a new division, and a new car he built to compete in it.

Last Saturday was his first race at this level. He finished first in his heat, drew P10 — position 10 — for the start of the feature race, and finished P2 — second place. On a dirt track, where cars run inches apart (often making contact) and the surface changes every lap, passing eight cars on opening night is a strong start.

“There’s no way you’re going to win every race, but if you’re consistently in the top five you have a pretty good chance to win the season on points,” says Andrew, happy with the outcome.

What Is Dirt Track Stock Car Racing?

Despite the name, stock cars share little with their factory model counterparts. They’re purpose-built machines — custom chassis, suspension, engine, and body panels — with fronts styled to resemble production sedans. Andrew’s wears a Camaro nose. Inside, a bucket seat and roll cage speak to the forces involved.

The household name in stock car racing is NASCAR, the sanctioning body behind the Daytona 500 and other paved-oval races. Andrew races on dirt tracks — packed clay, specifically — and the skill set is its own discipline entirely. The suspension sits higher and carries more attitude in the corners. Weight transfers dramatically. The rear swings wide. And the track evolves throughout the night as each race lays down rubber, moves clay, and changes the grip.

“There are so many different possible track conditions, and the course changes as the other races happen,” Andrew explains. “You often have to make mechanical adjustments before your race without testing them on the track, so there’s a little bit of strategy in that.”

On Saturday, for example, “I knew my car was over-gripping in the heat race,” he says. “But as the other races took place the track was becoming more slippery, so I decided not to make any adjustments this time and let the track conditions change to meet me.”

The results speak for themselves.

Between the Races

Opening night’s results were good. But this race gave Andrew a clear picture of what to dial in before the next one.

He plans to lengthen the wheelbase slightly on the right and shorten it on the left — a geometry change for tighter cornering. He’s also fitting a gear that lets the engine rev higher on the straightaway of the D-shaped track.

“Your cornering speed is key,” he says. “The faster you exit the corner, the more advantage you have in the straightaway.”

For someone who spends his weeks holding tight tolerances on precision CNC equipment, the instinct to build something exactly right doesn’t clock out when the shift ends.

Number 54

The racing season runs every weekend through the summer. Crystal Motor Speedway — Andrew’s Saturday track — draws drivers from across Michigan, and is one of the most well-attended dirt ovals in the state. In the off-season, those weekends shift to the garage: building, tuning, and readying the car for the following year.

Andrew races under number 54. His stepfather, Chaney Newland, carried it before him. His grandfather carried it first, starting in 1966. That number has meant something in this family for six decades — and once again it’s in Pro Stock.

The costs are real. Tires wear fast, requiring a fresh set nearly every other week, and fuel, parts, and repairs add up quickly. It’s a commitment that makes sense if you love the sport. Andrew clearly does.

Micron is proud to sponsor Andrew’s 2026 campaign. Follow his season or learn about sponsorship opportunities at his racing page, and catch him live at Crystal Motor Speedway.

Does your supplier risk profile account for what happens when a company’s leadership changes?

Most supply chain teams already have the most immediate indicators dialed in — financial stability, production capacity, quality certifications. And rightly so. But leadership continuity is a dimension that belongs in that same conversation, especially in the small-to-medium enterprise (SME) dominated landscape of CNC machining job shops.

As a third-generation, family-owned manufacturer, we think about this a lot. Our 70+ years of operation are the result of an intentional focus on continuity, and the result is something we’re proud of.

For supply chain professionals who are always looking to build a more complete picture of supplier health, succession planning status is a natural next addition to the framework you already have.

Six Succession Questions Worth Asking

These aren’t interrogation points, but conversation starters that help you understand the maturity of your supplier’s planning process. When approached from a framework of mutual growth, they demonstrate a customer who’s interested in their supplier’s long-term success:

1. Do you have a formal, documented succession plan in place for ownership and key leadership roles?
2. What specific processes are in place to develop and prepare identified successors?
3. Does a board or strategic planning group provide independent oversight to ensure alignment between current executives and the succession pipeline?
4. How is the financial transition — such as a buy-out or ownership transfer — structured to ensure stability during and after the handover?
5. What contingency plans exist for unexpected events, like the sudden departure or incapacitation of a key leader?
6. How frequently is the succession plan reviewed and updated to stay relevant to your business goals and market conditions?

You don’t need to work through all six in a single sitting or structure a separate meeting around them. They should fit naturally into your existing supplier review process.

What Good Answers Look Like

Suppliers with mature succession planning will answer these questions specifically and confidently. You might hear about identified successors who are already active in the business, written transition plans, or an advisory board that provides continuity of strategic direction independent of any one leader. These are genuinely positive indicators of organizational health.

If answers are vague or the topic hasn’t been formally addressed yet, that’s useful information too — worth noting in your supplier records and worth revisiting down the road. Many excellent suppliers are simply earlier in their planning process.

Tracking this doesn’t necessarily require a complicated scoring system — even a simple note on where a supplier appears to be in the process gives you meaningful context over time.

Why We Wrote This

Fielding critical questions like these from a customer is a challenge, but also an opportunity. As a supplier who’s taken succession planning seriously, we want to be asked.

We’ve put together a more comprehensive look at this topic — what the risks look like, how to evaluate where a supplier stands, and what a mature plan involves.

Read the full white paper here: Does Your Key CNC Machining Supplier Have a Succession Plan?

Or, browse our white paper library for more industry insights.