Deep hole drill machine

Normal drilling process

A deep hole is defined by its depth to diameter ratio (D:d), typically greater than 10:1.

Gundrilling is a precision process to drill deep holes in a variety of materials, from aluminum to superalloys.

Good finish, tight diameter control and straight-ness are part of the finished process.

Deep hole drilling is beneficial across several applications. Oil and gas exploration equipment, armaments, aerospace equipment, and engines are common applications for deep hole drilling and machining processes.

Advances in technology allow common CNC machining centers, equipped with high pressure through-spindle coolant, to be capable of gundrilling/STS-BTA.

What is Deep hole drilling?

Deep hole drilling

"What is considered a deep hole?"In general any hole more than 4 to 5 times its Diameter, is considered a deep hole.With conventional drills such as twist drills several cycles or pecks would be required to clear chips from the flutes of the drill. With a dedicated deep hole drilling machine and proper tooling and fixturing the hole can be produced in one pass. Depth to diameter ratios of up to 300:1 can be achieved. Good surface finish and hole size may eliminate secondary reaming, or honing operations.

"Which drilling method is right for my application .... Gundrill, BTA, Ejector?"

While many factors are involved in the choice of tooling and machine type Below are brief descriptions and general guidelines.

Gundrilling is an very old process of drilling long or deep holes, first used in the making of gun barrels more than 100 years ago. Today's technology with refined machinery and tool design has made gun drilling a reliable high production method for drilling short holes as well as deep holes. The gundrill consists of a hollow tube with a " V" shaped groove or flute along its length, and a carbide cutting tip designed in such a way as to produce it's own guide bushing as it drills the hole. High pressure coolant is introduced into the center of the drill tube through the spindle of the gun drilling machine to help break and evacuate the chips along the "V" groove of the tool and out of the hole. Gundrilling provides very close tolerance straight holes with excellent surface finish. Gundrilling is able to produce holes as small as .031"

Gundrilling

BTA or STS (single tube system) drilling is a process developed in more recent years, with BTA drilling the coolant is introduced around the drill tube at the pressure head, and chips are evacuated through the center of the drill. The detachable drill head is comprised of individual carbide inserts and guide pads. Very high penetration rates can be achieved with this system along with good surface finish. Diameters as small as .500" (12.7 mm) or as large as 15.00" (381mm) can be produced with this type of system.

BTA/STS

Ejector drilling or two tube system is a process similar to the BTA process except in this case the drill tube consists of an inner and outer tube. Coolant is introduced at the spindle via a rotary connector and passes between the inner and outer tube, chips exit through the inner tube. Minimum diameter is limited to about .750 (19 mm) since there is less room for chip removal in the smaller diameter tube. The ejector system performs well in the case where the face of the part is irregular since the design of the rotary connector and drill head create a venturi effect to draw coolant and chips through the inner tube with out relying on a good seal between part and bushing. The Ejector system is often adapted for use in lathes or machining centers.

Ejector

What method should I use for my application?Many factors are involved in the choice of tooling and machine type.

In general for diameters below 12.5mm gundrilling is the only choice, although some tooling manufacturers do make BTA tooling slightly smaller than this.

For diameters 12.5mm and above gundrilling may be more economical then BTA strictly on a cost per hole basis, but in the case where very high production rates are required, the number of spindles and initial equipment cost will be as much as three to five times higher with a gundrilling system, since in most cases, one two spindle BTA machine would easily produce the same or more parts per hour as one six spindle gundrill machine.

Other factors to consider are, the number of operators required, time required to change and regrind tools, and even the amount of floor space required.

For diameters larger than 50.8mm, BTA or Ejector tooling is probably the only choice.Ejector drilling is limited to diameters above 19mm does not require as high as pressure as the BTA system and works well when the part face is irregular or not machined square as it does not require a tight seal between bushing and work piece.

Gundrill, BTA or Ejector?

Auerbach make DHD machine

Sketch of DHD machine

Tools Accessories for Gun drilling

Tools Accessories for Gun drilling

Gundrill ToolingSmall diameter drilling, typically 1 - 50mm [0.04 -2.00in] diameter holesHigh-pressure coolant is introduced through the spindle and gundrill centerChips are discharged on the outside of the toolSpecial forms can be ground in tool tip

BTA/STS toolingLarger diameter drilling, typically 20 - 200mm [0.79 - 8 inch]Counter-boring and trepanning tools cover larger range, up to 500mm [20 inch] diameterHigh-pressure coolant is introduced around the outside of the toolChips are discharged through the tool center and machine spindleHigh penetration rates and power requirements compared to gundrill tooling

Drilling Tools

Drill tubes thread onto the cutting tool head and connect to the machine spindle, to transfer power to the tool during drilling.

Drill TubesBTA drill tubes come in standard sizes and securely connect the drill head with the machine. A solid connection is essential for accurate drilling.

Drill Tube ConnectionsDrill tubes are available in 4-start thread, 1-start thread, or flange connection styles for standard compatibility and easy installation.

Size and Type AdaptersDrill tube size or type adapters allow a single tube and durable tooling set to be used with an expanded range of tool heads.

Tools

After drilling, additional machining methods can further improve deep hole concentricity, straightness, surface finish, and more.

These methods machine the inside surface of the hole, much like other external machining processes, and most can be performed on a BTA deep hole drilling machine.

Processes are performed on a workpiece with an existing bore due to prior drilling or centrifugal casting, and an inside diameter surface exists.

Many of these deep hole machining processes have been optimized for specific applications, such as skiving machines for the hydraulic cylinder industry, or bottle boring for landing gear actuators.

Why BTA?

BTA Pressure HeadDirects coolant into the drilling process and mounts drill bushing and workholding components. UNISIG has pioneered the high performance series pressure head—maintaining accuracy while providing high thrust and radial load capacity for workpiece support while balancing internal pressures from cutting fluid delivery. This engineered system allows a wide tool diameter range with a single unit.

Pressure Head Rotating GroupPrecision rotating spindle with high thrust and radial load capacityBalanced fluid seal systemPrecision locating bore and pilot for workholding and tube seal installation

Complete Pressure Head AssemblyRotating groupWorkholding chucks or conesDrill bushing systemsTube seal packing glandsMounting framework

Accessories of DHD machine

Deep hole drilling with very long tools produces vibrations that must be dampened. Tuning the amount of dampening is an important factor in successful drilling.

Vibration Dampener CarriageFor rotating tool and stationary tool applications, the dampener carriage is used to mount devices to reduce vibration on the drill tube while drilling.

Dampener Cartridge/ManualPrecision rotating assembly with interchangeable collets to provide dampening to various drill tube size. Manually adjusted.

Dampener Cartridge/HydraulicPrecision rotating assembly with integral hydraulic cylinder to provide dampening to various drill tube sizes. Automatically or remotely adjusted.

Vibration Dampener Carriage and Cartridges

Cutting fluid is introduced to the tool and very high flow rates and pressure. Compared to conventional metal cutting processes, deep hole drilling requires very powerful pumps and precisely controlled delivery of coolant. UNISIG has refined the engineering for coolant systems, ranging from small gun drilling circuits operating at 200 bar (3,000psi) to high flow BTA systems delivering 1900 L/min (500 gal/min).

Coolant Temperature ControlRefrigerant ChillerUses a refrigerant compressor to actively remove heat from the cutting fluid.

Oil-Air Heat ExchangerUses the difference in the cutting fluid and ambient temperature to remove heat from the cutting fluid.

Oil-Water Heat ExchangerUses the difference in the cutting fluid and plant water temperature to remove heat from the cutting fluid.

Coolant Systems

Driver systems clamp onto drill tubes and secure the tube to the machine spindle. These precision components are manufactured from heat treated alloy steel, ground to ISO, ASME, or DIN standards.

Driver MountsThree types of mounts (baoyonet, direct, or adapter) are available to connect the tube to the spindle, and are based on international standards.

Split Clamps and Seal RingsVarious nominal sizes are available to match each machine's capacity. Split clamp reducers and tube seals allow a wide range of tools to be used with each size of flange mount.

Drill tube drive system

Drilled tube sheet

Handing of tube sheet

J-Preparation of Tube sheet

Cutting fluid parameters

THANK YOU