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Threading Tech Provides Answers to the Right Questions

Jim Lorincz
By Jim Lorincz Contributing Editor, SME Media
The multi-row design of the T2711 indexable thread mill, for sizes 7/8” (22.23 mm) and up, brings with it the advantages of thread milling, but the lower cutting forces keep the cycle time on par with tapping. (Provided by Walter USA)

It might be difficult to come up with definitive answers for all of the questions surrounding threading, but the effort to learn about advances in technology is well worth the effort when the results are measured. What are the best roles for solid carbide and indexable threading tools? What are the best solutions for difficult-to-machine materials? New coatings? Geometries? Leading suppliers have loaded their portfolios with the advanced tools to do the job. Here are a few of those tooling solutions and the rationale behind their development.

Market Forces, Innovation at Work

Technological advances and market forces have resulted in new developments in both indexable and solid carbide thread tooling, according to Jeff Dei, president of Carmex Precision Tools LLC, Richfield, Wis. “Nanotechnology coatings provide more accurate threads and longer tool life. Also, the advent of complex dies has led to the development of newer shapes, providing better cutting geometries,” he said.

In helical indexable tooling. Carmex’s vertical thread milling tools are available in both single- and multi-flute configurations. The multi-flute inserts are available with four to eight cutting edges and can be used both for internal and external threads. The helical shape delivers smooth cutting with low cutting forces, according to the company.

“Changes in the marketplace have also impacted tooling development,” said Dei. “For example, the trend towards smaller, more complex parts has resulted in increased demand for tooling designed for Swiss-style applications. Several of our lines, including Swiss Line, Tiny Tools and Mini Tools, offer the Carmex ‘helical advantage’ in those applications.”

Carmex has developed a wide selection of material-specific tooling in indexable and solid-carbide versions. “Applications involving hard-to-machine materials and high-temperature alloys have been largely responsible for the development of material-specific tooling,” said Dei. “Thanks to the development of new materials and nanotechnology, we are now able to match the correct coating or coatings to the substrate that will deliver the best results for the specific application. The Slim MT line, for example, which was designed for machining long threads from small to large diameters, utilizes a carbide/coating combination that provides both extended tool life and improved productivity in difficult materials.”

Front view of a four-insert CMT thread mill and holder in a vertical ID application. (Provided by Carmex Precision Tools)

In many cases, comparing the market share of carbide vs. indexable tooling is really a matter of “apples and oranges,” according to Dei. “For instance, carbide is a must for small-diameter internal applications, including many uses in Swiss-style machining,” he said. “The necessity of clamping and the advantages of multiple cutting edges limits indexable tooling to larger applications.”

Other factors to be considered when choosing between solid-carbide and indexable tooling include initial cost and whether the tooling is going to be used in a high-production or a low-volume application. “Some of the new technologies affecting the development of tooling for thread milling and turning include CAD and AutoCAD, which enable designers to experiment with new cutting geometries. Nanotechnology has greatly advanced coatings, and multiple coatings are becoming more common. Thanks to computer modeling, we can also employ stress analysis to optimize tool design,” Dei said.

He added that threading and milling advances are spurred by improvements in the machines producing the parts. “For example, many of today’s machines are lighter and faster, as opposed to earlier units that relied on mass and weight to reduce vibration,” said Dei. “Also, we are seeing more multi-purpose machines that combine both milling and turning. It’s up to us as toolmakers to see the ‘big picture’ and respond accordingly.”

Tapping Options for High Performance

YG-1 Tool Co., Vernon Hills, Illinois, offers a portfolio of taps that covers everything from the tool room to high-volume repetitive production, according to Mark Ford, YG-1’s director global product management–threading. “We divide our products into several different categories of metric and unified taps, including Combo Tap multipurpose taps with and without internal cooling,” said Ford. “Tools are designed around specific materials groups, including stainless steel, aluminum, high-temperature alloys and cast iron. Other tools are more application-specific, like pipe taps, roll form taps and thread inserts.”

A different option for threadmaking, YG-1’s popular 60° helical flute TiAlN-coated unified and metric thread mills are available with or without cooling. The combination multifunction tools drill, thread mill and chamfer in one setup and are especially well suited for niche applications. “It takes the right application and the right circumstances for these tools to be effective,” said Ford. “In the thread mill line, YG-1 offers pipe threads, NPT, NPTF, NSP and NPSF, though not gas pipe threads in the U.S.”

YG-1’s Synchro Tap has features and geometry that produce very little contact with the workpiece, allowing the tool to run at higher spindle speeds. (Provided by YG-1)

For high-speed tapping, YG-1’s Synchro Tap is designed to be extremely free cutting. “The Synchro Tap has very little contact with the workpiece and therefore can run at a much higher spindle speed. The tool has features and geometry to create free cutting. In tapping, your infeed or feed rate is fixed and is based on the pitch or lead of the tap. Your only option for productivity gains is to make the spindle go faster,” Ford explained. “Synchro Taps are designed to be run in a synchronous tapping cycle and held rigidly or, better yet, with a synchronous holder. That allows users to achieve two to three times greater spindle speeds than conventional taps.”

YG-1’s carbide taps are designed for cast materials, aluminum, and cast iron. They can achieve surface footage upward of 200 sfm, compared with conventional tap’s 150 sfm. “Carbide will absorb an enormous amount of heat and has outstanding wear characteristics, but it tends to be brittle,” said Ford. “Carbide taps require a little different mindset in handling and are well suited to high-volume applications like transfer lines for auto parts.”

To take the mystery out of selecting the correct tap for an application, Ford developed a training program he calls the 10 Questions to Success (see sidebar). “Answer these 10 questions and you are going to be much closer to success the first time around,” he said. “Shops often don’t know if they have the right tool because it’s such a nuanced little tool. Unlike a drill or an end mill, you can’t adjust your chip load or programming,” he said. “With a tap, you have to design that into the tool to overcome the inability to make adjustments on the fly. When running a tap, the control is such that it will only allow running at a certain percentage of the spindle speed. It’s the one tool where you drive to the bottom of the hole, stop and reverse back out. Every other round tool moves in a forward action.”

Thread Milling for Hard Materials

Tool breakage and scrapping are constant threats to successful threading of high-value workpieces like molds and dies and high-temperature alloys for aerospace applications. For threading difficult-to-machine materials, thread milling produces a high-quality thread with less tool pressure and less heat, according to Justin Ripple, product manager, Allied Machine & Engineering, Dover, Ohio. It also allows deeper threads for these materials.

Allied Machine supplies tools for complete holemaking, including roughing, reaming, threading and finishing holes for customers as diverse as mold and die and aerospace. “Thread milling allows our customers to use one thread mill to machine multiple diameters without having to stock a tap for each hole diameter,” said Ripple. “In addition, there is no removing a broken tap in a mold and die application where it is costly to scrap a high-value workpiece. Even the eye bolt that holds the die needs to be threaded. For those heat-resistant aerospace workpieces, thread milling produces less heat than other threading operations, which directly improves tool life.”

The most recent addition to Allied Machine’s thread milling products is the solid-carbide AccuThread T3, designed for machining hardened or difficult-to-machine materials, such as stainless steel, tool steel and high-temperature alloys.

Since its introduction, AccuThread T3 has been a “great success” so the line is being expanded with larger thread sizes up to 1”-8 UN and 24-3 ISO. (Provided by Allied Machine)

The premium AccuThread T3 solid-carbide thread mill is optimized for difficult-to-machine materials. “Since its introduction, AccuThread T3 has been a great success, so we are expanding the line with larger thread sizes up to 1"-8 UN and 24-3 ISO,” said Ripple. “The AccuThread T3 features AM210 multilayer PVD coating and includes left-hand cutting, allowing the tool to climb mill while it moves from top to bottom, creating a right-handed thread. Three cutting teeth cut minimal threads all at once and reduce side deflection as well as cut a precise thread form deeper into materials harder than 55 HRC, even reaching materials and customers with 60 HRC materials.”

For thread milling, machines must have three-axis simultaneous interpolation. For this operation, Allied offers Insta-Code programming downloadable from its website. Entering machining conditions and the desired thread will generate a program. “Insta-Code has been very popular and is being used by us and by our customers, who can add it as an engineering staff resource.” Also available from Allied Machine’s website is a link to its Thread Mill Pocket Guide with comprehensive information about different threads and cutting conditions.

In addition to solid-carbide tools, Allied Machine offers AccuThread replaceable insert thread mills in two styles, bolt-in and pin, for flexibility in meeting the variety of threading applications found in job shops.

Covering All the Threading Bases

Sandvik Coromant, Mebane, N.C., offers a comprehensive approach to internal and external thread turning with products and guidelines to optimize performance by material application and industry. The most important threading application considerations are chip control, insert wear, quality of thread and tool life, according to Kevin Burton, product specialist-turning team lead and Scott Lewis, industry specialist-aerospace. Threading performance depends on selecting the right insert type, geometry, infeed and programming for thread forms as diverse as general purpose and general use motion, aerospace, pipe thread and highly specialized proprietary threads for oil and gas industry applications, he said.

To maximize machining efficiency, Sandvik Coromant introduced the CoroThread 266 high-precision coolant solution with an iLock high-precision toolholder. “The CoroThread 266 is effective for all insert geometries, grades and thread profiles, and from low to high coolant pressures,” said Lewis. “The combination of over-coolant for chip formation and under-coolant for improved insert life produces higher product quality and machining efficiency as well as process security in all external thread turning applications.” CoroThread 288 delivers coolant pressure precisely to the cutting zone at more than 1,000 psi. “The iLock high-precision holder handles the extreme forces placed upon the insert, providing exceptional stability for ultimate accuracy, surface finish and product consistency,” Lewis said.

Sandvik Coromant’s wide assortment of threading grades and geometries covers the majority of materials and applications. Burton described the types of threading inserts and their geometries: “There are three different types of threading inserts: full profile for high productivity; V-profile 60° and 55° for most commonly used applications; and multi-point inserts for highly productive, economic threading in mass production.” Sandvik Coromant offers inserts in three geometries: all-purpose for use in a wide range of materials; F-sharp geometry for gummy or sticky materials; and C-chip breaking geometry for low carbon, alloy and some stainless materials.

Not to be overlooked, said Burton, are infeed type and insert inclination. “There are three different types of infeed which can have a significant impact on the thread machining process, affecting chip control, insert wear, thread quality and tool life. The choice of infeed method is influenced by the machine tool, insert geometry, workpiece material and thread pitch.”

Burton described the three infeed types—modified flank, radial and incremental—and their programming requirements:

Modified Flank Infeed: Most newer CNC machines can be programmed for modified flank infeed, which is used with C-geometry as the chip breaker won’t function with radial infeed. Axially directed cutting forces reduce the risk of vibrations and control chip direction. This is the first choice for most threading operations; the chip is similar to that in conventional turning, making it easier to form and guide.

Radial Infeed: Used by all manual machines and most canned CNC programs and the first choice for work hardening materials and suitable for fine pitches.

Incremental Infeed: Normally used with very large profiles and pitches or long work threading cycles where tool life needs to match the length of the thread. Chip control is difficult. Special programming is required.

According to Burton, GC1125 is the first choice grade for ISO P, M, K, and N materials in CoroThread 266. “This PVD-coated grade combines the superior wear resistance of a coated grade with the edge sharpness and toughness of an uncoated grade. Optimized for steel threading and for medium to high speeds. Benefits and features include high wear resistance and the possibility for fewer passes.”

Thread Turning Aerospace Materials

For thread turning, Iscar USA, Arlington, Texas, has introduced two new carbide grades, IC 806 and IC 1007, which are well-suited for aerospace materials. IC 806 has had great success in turning and became a good choice for threading, and IC 1007—a hard substrate with TiAIN PVD coating—was similarly effective for threading hard and aerospace material, according to Randy Hudgins, national product manager for turning and threading.

Iscar, which offers full lines of both thread milling and thread turning products, has introduced new insert products for thread turning that feature multi-cornered design. “Inserts have five or 10 corners versus two or three corners for standard lay-down threading,” said Hudgins. “The Pentacut format, for example, has five corners and the DecaIQ insert doubles up for 10 corners. DecaIQ threading is more for UN threads, standard threads up to 32 pitch down to 16. The Penta 27 is a wider insert that can create a wide thread geometry such as Acme, stub Acme or a lot of premium coupling threads for oil and gas.”

A major advancement to Iscar’s thread turning capability is the JHP high-pressure coolant delivery system with retractable nozzle for easy insert change. “With JHP we are able to get the coolant right into the cutting zone. In the case of many threads, like a 60° V thread, the insert comes to a very small point, which is fragile and very accessible to heat. Putting the coolant right into the cutting zone improves tool life significantly as well as chip control,” said Hudgins. “When cutting stainless and high-temp materials, getting coolant right into the cutting zone with high-pressure coolant makes the chips a little more brittle. Even if you aren’t going to break threading chips into 6’s and 9’s like turning, you can curl them up and make it so they aren’t wrapping around the part or around the tooling.”

In addition to ground inserts and pressed or molded inserts, Iscar offers a combination insert: the B-style insert is especially effective on aerospace materials. The B-style insert is a ground insert with a pressed chip former on the top of the insert which provides a sharp edge for shearing high temperature or gummy materials.

According to Hudgins, troubleshooting threading problems often turns up one of several issues. “One of the biggest issues with threading can often be solved by changing the infeed method—the angle of entry into the thread,” he said. “One of the easiest but least recommended is the straight zero-degree infeed, where you are engaging both sides of the insert at once. A lot of heat is created and using a modified flank infeed instead reduces the amount of heat in the cut and the amount of pressure in the cut and also protects the trailing edge. Another issue is that the machine may not always be on centerline, a condition that is caused by machine crashes and that can be easily corrected. Modern CNC machines and Swiss machines have the ability to offset the Y axis, alleviating the machine off center problem.”

Tool Selection Can Be the Solution

Threading problems may not be talked about much, but they exist. “It’s interesting that when talking to operators, programmers and engineers, if you ask them where they have trouble, almost nobody says threading,” said Luke Pollock, product manager, Walter USA LLC, Waukesha, Wis. “But everyone has had trouble with birdnesting or other chip issues when tapping. We normally try to push end users into thread forming or thread milling if possible. Taps have a very specific design depending on the materials or application, so that creates an issue of possibly making the tool selection very difficult.”

Walter, which carries a full line of products for tapping, thread forming and thread milling, has introduced a family of taps, TC117 and TC217, that is positioned in its Advance line for universal applications.

According to Pollock, the Walter lineup of products consists of three tool categories. Supreme indicates the highest level of technology and performance available; Perform tools provide an economical solution with focused importance on price; and Advance indicates a product efficiently balanced between price and performance. The Advance product family makes tool selection simple due to the universal application, meaning it will work in most materials, from ISO P, M, K and S. “And being a high performer with a competitive price, it’s at a level that most of Walter’s customers are looking for,” said Pollock.

Walter’s multi-row threadmills are normally viewed as problem solvers with tapered threads or fewer teeth to reduce chatter, according to Pollock. “But the Walter multi-row threadmills are designed so that the lower cutting forces allow feeding the tool faster and matching or reducing the cycle time compared to cut taps,” he  said. “We have two different styles: a solid-carbide version for threads less than 7/8” (TC620) and an indexable version for threads greater than 7/8” (T271x). These tools allow the user to gain all the advantages of thread milling—such as lower cost per thread and longer tool life—without sacrificing the cycle time.”

Innovative Tools for Threading Aluminum

To save critical machining time while producing high-quality internal threads in aluminum alloys, Emuge-Franken N.A., West Boylston, Mass., and Audi AG, Ingolstadt, Germany, worked on a new threading tool technology called Taptor that combines a twist drill with a tap.

Emuge-Franken Taptor technology saves time by eliminating pre-drilling and enabling higher cutting speeds. (Provided by Emuge-Franken)

“In conventional thread production, machining is carried out in two steps: step 1 is pre-drilling and step 2 is machining the threads using either taps, cold-forming taps or thread milling cutters,” said Mark Hatch, product director, adding that the required tool change results in longer machining times.

“Taptor features a unique drill section with a few threading teeth that are arranged axially at a small distance from the drill tip to produce threads in blind and through-holes, eliminating one entire machining process—the pre-drilling cycle,” Hatch said. “The core hole and thread are produced simultaneously in one operation by the Taptor tool, which was developed by Emuge-Franken. The process (Audi has applied a patent for it) is basically divided into two steps. In the first step, the movement of the tool corresponds to synchronous tapping. The drill feed per revolution therefore matches the thread pitch. In the second step, the tool cuts free at the drilling depth. And the thread teeth create a circumferential undercut. Then the Taptor is retracted through the generated thread.”

Used in conjunction with the Emuge Speedsynchro Taptor collet toolholder, which has an integrated transmission gear, a higher cutting speed can be achieved, according to Hatch. For example, when machining a cylinder head side with 26 threads M6 2×D in cast aluminum at 0.47” (12 mm) deep, Emuge-Franken reported a time savings of 41 percent, or two seconds per thread, when using the Taptor tool and the Speedsynchro Taptor collet toolholder combination.

Each thread produced corresponds to the specifications of DIN ISO 965 (Metric ISO thread). An undercut is created at the bottom of the thread, the length of which corresponds to the lead-in chamfer of a conventional threading tool. The screw can be screwed into this undercut. The Taptor process can be used on any machine that supports synchronous tapping and has a spindle with torque support and a tool magazine that can accommodate the Speedsynchro Taptor holder.

10 Questions Lead to Success

Answer these 10 questions and you will be much closer to threading success the first time around, according to YG-1’s Mark Ford:

What is the size, pitch and class of fit?

What are the gauge limits marked on the thread gauge?

What is the material being tapped?

What is the diameter of the hole?

What is the depth of the hole, and how much full thread is needed?

Is the application through-hole or blind hole?

Is the application vertical or horizontal?

What is the coolant capability of the machine and holding systems?

Can the threads be roll formed?

What are the coating requirements?

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