Deep Hole Drilling Tech Blog

Over the years I have been asked the same questions repeatedly by new operators, engineers, and shop managers. Here are the answers, with links to detailed articles for each topic. 1. What qualifies as a deep hole? A hole is considered deep when the depth-to-diameter ratio (L/D) exceeds 10:1. Below that, standard twist drills can handle the job. Above 10:1, you need specialized tooling and coolant systems. Full article: Deep Hole Drilling vs Conventional Drilling ...

A deep hole drilling machine is a significant capital investment — often $200,000 to $1 million depending on size and capability. The acceptance test is your only opportunity to verify the machine meets specifications before you are committed to it. I have been involved in several machine acceptance tests. Here is the procedure I use. Documentation Review Before any physical testing, I review the documentation: Machine specifications vs purchase order — confirm all options and features are present Electrical and hydraulic schematics Operator and maintenance manuals Spindle runout certificate from the manufacturer Coolant pump performance curve Alignment certificate from the manufacturer If any documentation is missing, I note it on the acceptance report. Missing manuals will cause problems later. ...

Pricing deep hole drilling work is not the same as pricing standard CNC work. The machine hour rate is higher, the tooling cost is significant, and the risk of scrapping a near-complete part affects the price. Here is how I calculate prices. Machine Hour Rate The machine hour rate is the foundation of any quote. I calculate it by dividing the total monthly cost of the machine by the number of billable hours. ...

Outsourcing deep hole drilling is different from outsourcing standard machining. The cost of a mistake — wrong tooling, inadequate coolant pressure, insufficient experience — is higher because the part is often 80% complete when the hole is drilled. I have worked with dozens of deep hole drilling vendors over the years. Here is how I evaluate them. What to Include in Your RFQ An incomplete RFQ produces an inaccurate quote. The vendor cannot price the job correctly without knowing all the requirements. ...

Carbide is the standard for gun drilling, but it is not always the best choice. In specific applications — high-silicon aluminum, hardened steels, and abrasive composites — PCD and CBN gun drills can outlast carbide by 10-50x. The catch is that these tools are expensive, brittle, and require a rigid setup. Here is what I have learned about when they work and when they do not. What PCD and CBN Are PCD (polycrystalline diamond) and CBN (cubic boron nitride) are superhard materials. PCD is the second-hardest known material after natural diamond. CBN is the second-hardest after PCD. ...

Hastelloy, Stellite, Monel, and Waspaloy are not as common as Inconel 718, but when a job comes in requiring one of them, the parameters that work for standard steel will not work at all. These materials combine work-hardening, abrasiveness, and low thermal conductivity in ways that punish mistakes. Here is what I have learned about drilling each one. Common Characteristics of Exotic Alloys All four of these materials share properties that make deep hole drilling difficult: ...

I get more questions about drilling small holes in Inconel 718 than almost any other topic. A recent Practical Machinist thread about drilling 3mm holes 160mm deep in Inconel 718 at HRC 40-45 got over 3,500 views. The user was struggling with drill breakage, centerline deviation, and surface finish. The root cause in that thread was the same one I see most often: coolant pressure at 8 bar (116 psi) when the job needs 100 bar or more. Here is what I have learned about getting this application right. ...

Scrap in deep hole drilling is more expensive than scrap in most other machining operations. By the time the hole is drilled, the part has already been turned, heat-treated, and faced. A scrapped bore means all that upstream work is lost. I have worked on reducing scrap rates across multiple shops. The approach that works is not complex — it is systematic. Track What You Are Scrapping The first step in reducing scrap is knowing what you are scrapping and why. Without data, you are guessing. ...

The paperwork side of deep hole drilling has grown significantly over the years. Customers who used to accept a simple dimensional report now require material certifications, process validation, and full inspection data for every batch. I have adapted my documentation system to meet these requirements without slowing down production. Here is what I document and how. What Customers Typically Require The level of documentation depends on the industry and application. Here is what I see most often: ...

I used to think chip breaking was entirely about feed rate. If the chips were too long, I increased the feed until they broke. That works up to a point, but the drill’s chip breaker geometry sets the baseline for what feed rate will work. Understanding chip breaker geometry helps you choose the right drill for the material and know whether a regrind is maintaining the correct geometry. What a Chip Breaker Does A chip breaker is a groove or step ground into the rake face of the gun drill tip, just behind the cutting edge. As the chip slides across the rake face, it hits the chip breaker and curls. The curl creates bending stress in the chip, and when that stress exceeds the material’s fracture limit, the chip breaks. ...