The EMUGE A-H family of taps is suitable for short chipping hardened steel and cast iron. EMUGE-FRANKEN
Depending on a part’s design and function, a hard material may be required. Specific materials and hardnesses are used to reduce part wear and increase longevity. Hard materials, typically alloy steels, are classified as greater than or equal to 44 HRC. When choosing to tap hard material internal threads, the material hardness should be less than 55 HRC. Tapping materials greater than 55 HRC isn’t practical.
In fact, threading hardened materials with taps can be a secondary consideration because thread milling is typically the preferred method in very hard materials. There is less load on the tool and reduced heat, as well as greater wear resistance when using thread mills.
To determine if tapping is viable for your hard material application, first establish its hardness rating. Once you know the hardness of the material, ask yourself: “Why am I trying to tap this versus thread mill this?” If the choice is still to tap, the most practical scenario is when you tap sizes UNC ¼" to ½", and M6 to M12. On holes smaller than ¼" and M6, a tap cannot withstand the torque required. In holes larger than ½" and M12, the thread pitch is coarse, radially deep and has a large diameter, resulting in high torque and heat when tapping.
Here are some additional tips:
- Use a tap designed with a substrate, geometry and coating specifically engineered for hard materials. A coated tool must be used to reduce the wear of the substrate. Also, the tap must be made of a material that has the properties to withstand high torque and high heat at the cutting edge, and abrasion of the material. Taps comprised of tool steels with powder metallurgy (PM) construction and solid carbide should be used. For example, the EMUGE A-H family of taps is comprised of premium HSSE and HSSE-PM taps for hardened steel and cast iron materials. A-H taps are available with or without coolant through holes, and with TiCN coating, or NT nitride surface treatment, for improved tool life. Premium HSS-E A-H taps are for materials up to 48 Rc hardness. Emuge HSSE-PM A-HCUT taps are for materials between 44 Rc and 55 Rc hardness and feature a hard, heat-resistant, powdered metal substrate for enhanced cutting performance and extended tool life. The taps with TiCN coating enhance the surface hardness and help increase the tools’ abrasion resistance.
- Use a tap drill that is at the maximum minor diameter tolerance.
- Since tapping hard materials produces a lot of heat, coolant isn’t adequate. Coolant doesn’t have enough lubricity to assist the tap. It is advisable to use tapping oil or paste to provide high lubrication to reduce the development of heat from cutting and friction.
- The toolholder is extremely important and integral to the success of the tap, and it is recommended to use an axial floating tap holder. Hardened materials do not move — they are very strong. Any pitch error of the machine tool will wear or break the tap quickly because of the excessive torque and pressure. Using an Emuge Softsynchro® tap holder or an Emuge KSN tension compression tap holder will compensate for the machine tool pitch error. These holders ensure that the tap performance is only impacted by the material type and hardness, not the machine tool.
- Hard tapping is a slow process, and the primary goal is to achieve a thread to tolerance without breaking the tap. Use a low cutting speed, 5 sfm for 44 HRC to 50 HRC, and 3 sfm for 50 HRC to 55 HRC.
Related Glossary Terms
- alloy steels
alloy steels
Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, sulfur and phosphorus) added to cause changes in the metal’s mechanical and/or physical properties. Principal alloying elements are nickel, chromium, molybdenum and silicon. Some grades of alloy steels contain one or more of these elements: vanadium, boron, lead and copper.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- cutting speed
cutting speed
Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- hardness
hardness
Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.
- lapping compound( powder)
lapping compound( powder)
Light, abrasive material used for finishing a surface.
- lubricity
lubricity
Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.
- milling
milling
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- pitch
pitch
1. On a saw blade, the number of teeth per inch. 2. In threading, the number of threads per inch.
- powder metallurgy
powder metallurgy
Processes in which metallic particles are fused under various combinations of heat and pressure to create solid metals.
- tap
tap
Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.
- tapping
tapping
Machining operation in which a tap, with teeth on its periphery, cuts internal threads in a predrilled hole having a smaller diameter than the tap diameter. Threads are formed by a combined rotary and axial-relative motion between tap and workpiece. See tap.
- threading
threading
Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.
- titanium carbonitride ( TiCN)
titanium carbonitride ( TiCN)
Often used as a tool coating. See coated tools.
- tolerance
tolerance
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
- tool steels
tool steels
Group of alloy steels which, after proper heat treatment, provide the combination of properties required for cutting tool and die applications. The American Iron and Steel Institute divides tool steels into six major categories: water hardening, shock resisting, cold work, hot work, special purpose and high speed.
- toolholder
toolholder
Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.
- wear resistance
wear resistance
Ability of the tool to withstand stresses that cause it to wear during cutting; an attribute linked to alloy composition, base material, thermal conditions, type of tooling and operation and other variables.
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