Deep Hole Drilling Tech Blog

Estimating cycle time for deep hole drilling is straightforward if you break it into parts. I have been quoting jobs for over a decade, and the formula below has served me well across gun drilling, BTA, and ejector drilling. The total cycle time determines whether a job is profitable. Miss it by 20% and you either lose the quote or lose money on every part. Here is how I calculate it. ...

A fixture is a custom workholding device designed for a specific part. Unlike standard chucks and steady rests, fixtures are built to match the part geometry exactly. A good fixture reduces setup time and improves consistency. I’ve designed and used fixtures for all types of deep hole drilling work. The same principles apply regardless of the part shape. Design Principles Support the part at the bore location. The most important principle. The part should be supported as close as possible to where the drill enters and exits. Unsupported span allows the part to deflect. ...

Coolant selection determines tool life, surface finish, and hole quality in deep hole drilling more than any other process parameter. The right coolant makes the difference between a 500-hole tool life and a 2000-hole tool life in the same material. Here is what I use and why. Coolant Types Overview Three coolant types cover almost all deep hole drilling applications. Each has trade-offs in performance, cost, and maintenance. Type Lubricity Cooling Cost per Liter Filtration Requirement Best Application Neat oil Excellent Good $3 - $8 10 - 20 μm Gun drilling, BTA, demanding finishes Emulsion (oil-water) Good Excellent $0.50 - $1.50 20 - 50 μm General deep hole drilling Synthetic Moderate Excellent $1 - $3 20 - 50 μm High-speed work, aluminum Oil-Based Coolants Oil-based coolants provide the best lubrication for gun drilling. I use neat cutting oil for all critical gun drilling and BTA jobs. The oil film between the guide pads and the bore wall reduces friction by 30-50% compared to water-based coolants. ...

Aerospace deep hole drilling is the most demanding work I’ve done. The materials are expensive, the tolerances are tight, and the cost of a scrapped part can be five figures. Every hole needs to be right the first time. The main applications I’ve seen are landing gear components, engine shafts, and hydraulic actuators. They all have the same challenge: deep holes in tough materials with no margin for error. The Material Challenge Aerospace parts are typically titanium (Ti-6Al-4V), Inconel (718 or 625), or high-strength steel like 300M. All of them are harder to drill than standard engineering materials. ...

Agricultural and forestry equipment is a steady market for deep hole drilling. Tractors, harvesters, loaders, and loggers all use hydraulic cylinders for their working functions. Every cylinder needs a drilled bore, and every rod needs a drilled hole if it’s hollow for weight reduction. I’ve worked on components for several agricultural and forestry equipment manufacturers. The work is similar to construction equipment but with some differences in volume and pricing. ...

Brake system components need deep hole drilling for fluid passages, weight reduction, and in some cases, cooling. The work is safety-critical, and the quality requirements reflect that. I have worked on brake components for passenger cars and commercial vehicles. I have personally overseen the drilling of over 50,000 caliper and master cylinder bores without a single field failure attributable to the drilling operation. The drilling operations are straightforward, but the inspection and documentation requirements are more demanding than for non-safety components. ...

Construction and mining equipment is one of the biggest markets for deep hole drilling, even though most people do not think of it that way. Every hydraulic excavator, bulldozer, dump truck, and drill rig has cylinders that need deep drilled bores. The volumes are higher than aerospace, and the parts are bigger than automotive. I have worked on cylinders for excavators, loaders, and mining trucks. The work has its own character. ...

Couplings and universal joints are components that connect rotating shafts. They often need through-holes for weight reduction, lubrication, or assembly access. The drilling work is similar to general shaft work but with some specific requirements. I have drilled components for industrial couplings, automotive driveline U-joints, and heavy equipment shaft connections. The tolerances and volumes vary widely across these applications, which means I adjust the process for each one. Coupling Hubs Coupling hubs are the parts that mount on the ends of shafts. They typically have a through-bore that matches the shaft diameter and may have additional cross-holes for keyways or set screws. ...

I’ve been seeing more EV motor shaft work in the last couple years. The pattern is consistent: a shaft maybe 300-600mm long, 30-50mm OD, with a through-hole of 10-25mm that needs to be straight and smooth over the full length. The reason is weight reduction. A hollow shaft spins up faster and puts less load on the bearings than a solid one. And the balance is better — which matters when the motor is spinning at 15,000 RPM or more. (If you’re more familiar with gun drilling solid shafts, the hollow ones have their own quirks.) ...

Fasteners are not the first thing that comes to mind for deep hole drilling, but I have drilled plenty of bolts and threaded rods that needed a through-hole for safety wiring, weight reduction, or lubrication passages. The applications range from aerospace fasteners to oil and gas stud bolts that need center bores for hydraulic tensioning. The challenge is that fasteners are usually hardened, and they are mass-produced — so the deep hole drilling needs to be fast, consistent, and gentle on the threads. A bolt with crushed threads is scrap regardless of how good the through-hole is. ...