For deep-hole drilling, part-handling might be the most visible automation element, but it’s not necessarily the most impactful. Often, it’s internal process automation that yields the most significant results even with a manually loaded drilling machine.


Deep-Hole Drilling Automation Is More Than Part Load/Unload


For deep-hole drilling, part-handling might be the most visible automation element, but it’s not necessarily the most impactful. Often, it’s internal process automation that yields the most significant results even with a manually loaded drilling machine.

When it comes to automating deep-hole drilling, there are challenges unique to the process itself. These include fixturing complexities — where maintaining alignment requires elements such as guide bushings and tool supports not present in a conventional lathe or milling machine — and part attributes such as length and weight.

Long parts mean a long drilling cycle time, and maintaining production rates often requires multi-spindle, deep-hole drilling systems. Unfortunately, stopping a two- or four-spindle machine means two or four spindles sit idle until the parts are loaded and unloaded. So, in these instances, the more parts in the machine at one time, the more automation can actually inhibit cycle time while the machine is running.

Solving this problem in multi-spindle machines requires internal automation to achieve the objectives of lean manufacturing and one-piece flow. In-machine loaders singulate processes so that even within a small four-piece batch you maintain one-piece flow. The operator or automation device puts in a part and takes a part out, and the machine does a bit of maneuvering inside to sequence those four parts in such a way as to minimize spindle downtime while maintaining upstream and downstream processes for one-piece flow. For instance, parts could be loaded onto a smart conveyor, indexed, and lifted into chucks for the drilling cycle before robotic unloading on the out-feed side so that there are no bottlenecks to a steady production flow.

Tool life management is another form of internal automation. Getting feedback to the machine enables the deep-hole drilling process to adapt or halt, if necessary, before tools and parts are damaged.

Tool life management is built into a machine’s control, and the machine senses torque thrust and coolant. Chip condition is usually the first indicator of wear, which would otherwise require an operator present to detect, so the machine actually monitors the process and can predict tools starting to wear and identify when they need to be changed. A tool life management system also can count distances drilled and the number of cycles, then prompt  a tool change at the appropriate time.

That kind of in-machine automation smooths the path for external automation. As the process builds, highly standardized options for robot-ready machines such as an automatic door, workpiece-present sensors and programmable workpiece fixturing makes it easier to add a robot at a later date. These robot-ready machines also create efficiencies before they’re fully automated. Even with manual loading, the automatic doors and programmable clamping make the process more efficient.

In UNISIG’s experience, an embedded reamer tool changer enables manufacturers to manage significant throughput increases, even with an operator. With this technology, operators can maintain the pace of production loading the machine, while eliminating the task of inserting reaming tools for each cycle. This allows the operator to redirect efforts towards tasks such as additional quality checks and off-machine setups.

Picture yourself facing knee surgery, under the care of a skilled orthopedic surgeon. Precision instruments, state-of-the-art monitoring equipment, and decades of experience


How to Drill Straighter: Concentricity in Deep Hole Drilling

Picture yourself facing knee surgery, under the care of a skilled orthopedic surgeon. Precision instruments, state-of-the-art monitoring equipment, and decades of experience are on hand, as they conduct a procedure that will ideally lead to more days on the court. The surgical team works patiently and carefully towards a successful outcome, relying on tools to guide their movements with exact precision, placing instruments exactly where they need to be in the body, and not even a half millimeter off. For deep holes in components to be accurate – including surgical tooling – they need to uphold tight concentricity tolerances, and in gundrilling, this happens best with counter-rotation. For a manufacturer, this is vitally important. For an end user, or in this case a patient facing surgery, it can make all the difference.

These precision parts are one of several applications that have deep holes, where concentricity is critical to the function of the part. Concentricity tolerances are achieved when the hole follows the desired axis of the part, eliminating drift from the point of entrance to the exit. In a round part with on-center drilling, this is easily illustrated; some applications may include deep holes which are off-center, or in non-round parts, but still have tight concentricity requirements.

Low concentricity in some applications can result in parts with weak sidewalls, mismatched holes, or even scrapped parts. In other cases, manufacturers may decline production of these components, because of perceived impossibility or unproductiveness. With the addition of a counter-rotating process on deep hole drilling equipment, critical concentricity tolerances can become both achievable and economical.

How Counter-Rotation Improves Concentricity

Drilling a deep hole is commonly achieved by rotating the cutting surface of a tool against the metal of a workpiece with two opposing spindles in a horizontal setup. Typically, this consists of a stationary workpiece and rotating tool, but can also be configured with a rotating workpiece and stationary tool, or a third option, with a counter-rotating tool and workpiece.

Common machining centers use a rotating cutting tool, such as a mill, and a fixtured, stationary workpiece. A lathe, alternatively, rotates a workpiece and cuts with a stationary tool. Much of the time, setups such as these are enough to achieve the goals and tolerances of a majority metal cutting tasks, but are limited when it comes to more extreme tolerances and depth-to-diameter ratios.

A tool-rotate configuration is the least accurate when it comes to concentricity. In this setup, gravity is believed to act on the base and shank of the tool, not the drilling tip, and along with the rotation of the tool. Because of the relative position of the tool and gravity to the workpiece, this configuration produces the poorest results. This tool-rotate process is common for shallower holes on a machining center, but as holes become deeper, and tolerances become tighter, this no longer works as a solution.

Workpiece-rotate-only setups produce holes that are approximately twice as concentric as tool-rotate. A rotating workpiece changes the relative force of gravity compared to the workpiece position, negating some of the effects on the finished hole. A rotating workpiece can be done on a lathe with limited capability, but is ideally performed on a dedicated deep hole drilling machine.

deep hole drilling diagramCounter rotating tool and workpiece improve significantly upon both of these, as the forces are never static – changing relative gravity and orientation will provide drilling conditions without a single constant net direction that the tool will follow. In this setup, the tool is restricted from drifting, and will produce a much more concentric finished hole.

Counter-rotation is easily achievable with the right equipment and setup, whether it is for smaller gundrilled holes, or larger, longer BTA drilled components.

Deep holes are typically classified as anything with a depth-to-diameter (D:d) ratio of approximately 10:1 or greater, and can even reach extreme ratios of 100:1. As deep holes approach ratios of 20:1 or greater, drilling with specialty tooling on dedicated equipment is optimal. Modern deep hole drilling machines are designed to maximize the potential of tools such as gundrill and BTA processes.

deep hole diagram

The Data

To represent the impact of counter rotation, a test was performed on a 4140HT workpiece, 30 inches in length, ¾” outer diameter and a ¼” drilled hole. The depth to diameter (D:d) of this test is 120:1. This part is easily representative of a power transmission shaft or aerospace linkage.

Drilling these test workpieces produced the following results (measured using ultrasound):

  • Rotating Tool, Stationary Work: 0.026 inch drift at 30 inches of drill length
  • Stationary Tool, Rotating Work: 0.015 inch drift at 30 inches of drill length
  • Rotating Tool, Counter Rotate Work: 0.009 inch drift at 30 inches of drill length
    *results may vary based on material, depth-diameter ratio, tooling, etc.

Drilling holes with a 40:1 or less depth-diameter ratio can be done with limited drift using standard drilling practices. Beyond 40:1, counter-rotation really begins to deliver benefits with minimal drift.

Total Drift Comparison, Drilling Methods

  • Rotating Tool - Stationary Workpiece
  • Stationary Tool - Rotating Workpiece
  • Counter-Rotating Tool and Workpiece

Getting Started with Counter-Rotating Deep Hole Drilling

Typical machining centers are often not capable of deep holes greater than a 20:1 D:d ratio, and are not configured for counter-rotation. Rather, dedicated deep hole drilling machines are a superior consideration because they are designed specifically to manage accurate counter-rotation in gundrilling and BTA processes.

Deep hole drilling machines that enable successful counter-rotation include the right components, machined and assembled to maintain superior alignment. These range from the machine base, to rotating bearing groups and spindles, to tool and workpiece support – all of which uphold alignment and work as a system. This allows the machine to maintain accuracy while moving, and hold concentricity tolerances throughout the depth of the hole.

rotating deep hole drilling workpieceFor deep hole machine builders, alignment considerations begin with the machine base. Each component is designed with alignment as a priority,as well as machining and environmental factors like temperature and gravity. Counter rotation may be possible on machines retrofitted with a second rotating group, but will often need to undergo an alignment improvement process which creates additional challenges. Equipment designed with this purpose will have the right combination of benefits to make concentricity tolerances manageable for nearly any operator.

On a counter-rotating drilling machine, a good operator interface will provide a full picture of process information, as well as allow control over process parameters, for fine-tuning and process repetition. Manufacturers can optimize their counter rotation application, and proceed into highly accurate and efficient production.

A general starting point for counter rotation is to allow one third of the total speed to come from the workpiece, and two thirds of the speed to come from the tool. This is a typically recommended starting point for counter-rotating drilling with confidence. Operators can adjust for their specific application, and work with industry partners for recommended parameters to meet deep hole drilling goals.

Productivity Considerations

The addition of counter-rotation in a deep hole drilling process gives operators an additional factor to optimize for both specification and production requirements. The ability to hold improved concentricity tolerances with counter-rotation allows feeds to be run at optimal rates, as well as extends tool life. Manufacturers can reliably produce more parts per hour, with fewer tool changes and improved tool consumption.

For applications where concentricity is indeed critical, the productivity benefits are significant, and easily justify the added capability. Counter-rotation consistently produces a more concentric drilled hole, typically with higher surface cutting speeds, offering clear benefits to manufacturers in both accuracy and efficiency.

Manufacturers can increase capability, improve hole tolerances, and optimize productivity, ultimately cutting costs and providing a competitive manufacturing advantage. With the right resources, drilling deep holes with extreme concentricity is economical, repeatable, and commercially viable.

Match Grade Machine, a specialty manufacturer of standard and custom single shot rifle and pistol barrels, stands out in their industry for their exceptional accuracy and attention to detail, complimented with a proven record for fast delivery to customers' hands.


Taking Control of Barrel Blank Production | Case Study

Industry: Firearms

Customer Product: Specialty Rifle Barrels

UNISIG Solution: Firearms Industry Production Cell

rifled custom barrels
Match Grade Machine, a specialty manufacturer of standard and custom single shot rifle and pistol barrels, stands out in their industry for their exceptional accuracy and attention to detail, complimented with a proven record for fast delivery to customers’ hands. The reputation of their products, as well as their high level of customer service and responsiveness, is vital to their long standing success and brand integrity.

Image Credit: Match Grade Machine

Dylan Sip, owner of Match Grade, is always conscious of opportunities to improve his company and advance their balance of brand and product values. Being able to offer top quality barrels, at a competitive price point, with the fastest lead times to market is what has earned them their place in the market. Continue reading“Taking Control of Barrel Blank Production | Case Study”

The modern gundrill is an engineering marvel, a well-designed piece of equipment that does one thing exceptionally well. A new gundrill will produce round, straight holes with enhanced cylindricity even at its deepest points.


Time to Rethink Resharpening Gundrills

By Eric Krueger and Ryan Funk, Engineering Team, UNISIG
Originally posted in Manufacturing News

The modern gundrill is an engineering marvel, a well-designed piece of equipment that does one thing exceptionally well. A new gundrill will produce round, straight holes with enhanced cylindricity even at its deepest points. And it does all this while simultaneously providing a fine I.D. finish and excellent tool life.

Like all tools, gundrills wear out, typically after drilling around 1,000″. While a talented operator can still drill a hole with a worn gundrill, it will more often result in a loss of hole tolerance and finish at best. As gundrills wear, they require more thrust and torque while producing more run-out and experiencing greater drift. A dull cutting edge will produce irregular chips, which in turn cause spikes in coolant pressure – sure signs that failure is imminent.

Unlike some tools, gundrills are excellent candidates for resharpening. When performed correctly, the same gundrill can be resharpened to perform as well as a new drill as many as 8 to 10 times. The only significant difference between a resharpened gundrill and a freshly produced tool from the OEM is a slight back taper, an issue only for shops that require tolerances far beyond most manufacturers’ needs – all other shops can simply account for the ever-so-slightly reduced tool diameter. Otherwise, the only visible difference will be seen in the length of solid carbide on the gundrill’s tip.

Even coated drills can be sharpened. Naturally, this will reveal the raw carbide on the face, but this does not impact performance. The coating will remain on the wear pads and continue to improve the gundrill’s size control and ability to leave behind a finished surface. Tool life will be impacted, but the only other option is having it fully resharpened and re-coated by the OEM, which will likely be less cost effective.

Manufacturers have several options for resharpening their gundrills. For specialized gundrills, such as twin-flute tools and those intended for ultra-high-feed applications with chipbreakers below a coating, resharpening is something that only a gundrill’s OEM can do. A local sharpening service will likely have the proper equipment, but this requires having redundant tooling and factoring in lead time and transportation costs.

However, both of these methods result in a loss of process intelligence. The grinding process can offer valuable information manufacturers can use to optimize their gundrilling applications. As a result, more manufacturers that use gundrills are choosing to resharpen their tools in-house.

The main risk of performing resharpening operations in-house is poorly sharpened gundrills. Without the correct tip geometry, gundrills do everything worse: size control, roundness, cylindricity, finish, chip control, straightness and depth all negatively impact workpiece quality and result in significantly diminished tool life. This will cause operators to reduce feedrates or change out tools more frequently to achieve the necessary tolerances and out of fear of catastrophic tool failure.

Modern gundrill grinding systems make it easy to avoid these consequences. For the greatest advantage, one needs the full system. That means a grinder, the appropriate gundrill fixture and equipment for calibrating and inspecting the drill tip.

A basic, high-precision manual tool grinder is used as a platform for these systems, though the length of some gundrills necessitates a reinforced table for sufficient accuracy. Choosing a fixture can be more complicated, as gundrills can be ground in two different ways. Sweep grinding leaves behind a gradual transition between elements of the tip’s geometry, while facet grinding creates distinct geometry. UNISIG typically recommends facet grinding, because the slight increase in tip strength produced by a sweep grind is outweighed by the repeatability and greater ease of inspection offered by facet grinds.

The final piece of advanced gundrill grinding systems involves a digital inspection camera capable of viewing and storing magnified images. Ideally, this will allow the user to perform measurements and identify flaws without taking the tool out of the fixture. In addition to allowing for highly precise grinding, this inspection is vital for process optimization.

Process optimization capability is the real added value conferred by performing gundrill resharpening in-house. Frequent inspection allows for the maximization of tool life. Shops become familiar with the wear patterns created by a given application and may find they are replacing gundrills too often. If a gundrill tip has even wear across its entire cutting edge, it could easily have many hundreds of inches of life left, something that will only become apparent with repeated inspections.

In-house gundrill resharpening also ensures that shops can obtain the best tip geometry for their given applications. Whether it is uneven or unexpected wear, or the sudden appearance of chips in the cutting edge, once a shop identifies an irregularity, they can then adjust speeds and feeds to optimize the process. The inspection equipment even makes working with tooling OEMs easier, since shops can send them a measurement set and picture of a tool when asking for advice on how to improve the geometry.

With more experience, it becomes possible to tie a wear condition back to the process. For example, if there is a visible build-up along the cutting edge, it is often because the rotational speed is too slow. Conversely, if the edge is wearing faster than the tooling supplier’s data suggests, the tool is likely spinning too fast. Meanwhile, a chipped cutting edge suggests the feedrate was too high. With this know-how, shops can optimize the process and avoid future problems.

Fortunately, modern gundrill grinding systems make developing this know-how easy to achieve; in fact, the process usually takes longer to describe than it does to perform. After clamping in the gundrill, an operator can use geometry data from the tooling supplier to calibrate the camera. With the latest human-machine interface software, this can be as simple as drawing a line on the screen to establish the known gundrill diameter for repeatability purposes.

After calibration is complete, grinding can begin. The grinding wheel, turning in the direction toward the drill edge, makes contact with the drill tip after the operator confirms the correct rotational and X- and Z-axis orientations. A standard starting point grind will begin with the tip angled at +30° horizontally and +15° vertically with the rotation at +5°. The Y-axis is used to hold the tip to the grinder while feed is performed along the Z-axis at a rate of about 0.002″ per pass.

Some gundrills include an outer secondary angle parallel to the front cutting edge where the primary and secondary angles meet. It is critical that this primary facet is relatively narrow, since too much width will increase heat production and, consequently, reduce tool life. The operator next moves to the inner relief facet by moving the grind fixture -20° vertically in the opposite direction from the primary angle. This movement results in the formation of a point position with a length that is exactly 1/4 of the drill’s diameter, or the “D/4″ position, but other lengths may be necessary depending on the material.

Next, the operator moves to the front clearance, a facet with a point close to – but not touching – the front cutting edge. With standard gundrill tip geometry, a 0° horizontal angle and rotation as well as a +26° vertical angle will provide the correct position. While cutting performance improves the closer this point gets to the cutting edge, optimal edge strength requires placing the point slightly behind the edge. If a tip’s geometry requires an outer secondary angle, the front clearance facet’s point should meet it. Otherwise, the point of the facet is placed between 0.02″ and 0.03” behind the front cutting edge.

The final step on the grinder provides the oil dub-off, a facet with an edge tangential to the flute of the gun drill. Operators position the grind fixture at -30° horizontally, +25° vertically and +65° rotationally. The gundrill tip then feeds into the grinder at a rate that prevents cutting into the front cutting edge. The optimal angle meets the inner relief angle at the corner opposite the gundrill’s outside diameter.

After grinding is complete, the operator can use a hand chamfer to create additional clearance for optimal performance. The finished gundrill is now resharpened and ready for use – a process that takes fewer than 10 minutes. Given the ease of use and the significant process optimization opportunities, it is time to re-think gundrill resharpening.

Reposted with permission.