Which CNC knee mills offer the biggest technological bang for a small U.S. custom molder’s buck—especially when said molder is upgrading from a manual knee mill? IMM wanted to know, so we interviewed you and we sent out an RFQ, too.

Although it may be hard to come across certain kinds of calendars hung on the walls of most custom molders’ toolrooms these days, one thing you’re almost sure to spot is a Bridgeport. Historians say that ever since the Bridgeport Machine Tool Co. introduced its new type of vertical knee mill in 1936, the term “Bridgeport” has become synonymous with such mills. Why?

According to the folks at the online Virtual Machine Shop, it was because Bridgeport advanced the “state of the tech.” “Although they did not invent the concept of vertical milling, they did introduce a revolving turret and ram system that allowed the milling head to be positioned anywhere over the table. This idea has been copied into every other brand of vertical knee mill today. So popular was the Bridgeport mill that many seasoned machinists still call all vertical knee mills Bridgeports.”

Everyone agrees that the next really big shift in vertical knee mill technology occurred in the 1970s with the proliferation of CNC machine control systems. Chief among the other benefits they provided, such as bottom-line improvements in milling speed and precision, CNC controls allowed vertical knee mills to move their spindles along the vertical axis (the z-axis), providing a new degree of surface creation freedom.

What’s the state of the tech in CNC knee mills today? To find out, we sent out another imaginary RFQ from our imaginary molding company, we spoke to a few of you, and we also spoke to a guy who says his invention was the next big breakthrough.

Control freedom

Our guest inventor is Dwayne Elrod, president of Elrod Machine & Mfg. Inc. (Flagstaff, AZ). “CNC knee mills are what we do—it’s my passion and ambition in life,” Elrod says. EMM builds CNC retrofits and its own brand of vertical knee mills.

“When most molders go shopping for a new CNC vertical knee mill, most lean toward looking just at the CNC controller, saying to themselves, ‘Well, this controller can do this, and it doesn’t do that.’” Elrod believed a mill’s hardware is just as important as its software, especially when it comes to a mill’s quill drive, as we’ll see.

Still, he agrees that the advent of CNC controls changed everything. “CNC controls increased machining capabilities, oh, tenfold or so, conservatively speaking. Back in the ‘70s, if you wanted to do some top contour work, you needed a rotary table. You spent more time positioning and less time cutting.

“CNC controls let you use the whole table—the complete machine. It gave us the capability to do more with our machines, including three-axis work. Before that we could only do two-axis work. Now, with CNC control, we can do the type of work on a knee mill that’s normally done on a machining center.”

Although there are a number of good controls suppliers in business these days, Elrod says these are the four most popular:

• Centroid (Howard, PA); Elrod uses these

• Fagor Automation (Elk Grove Village, IL)

• Heidenhain Corp. (Schaumburg, IL), which distributes CNC controls from Acu-Rite Cos. Inc. and Anilam, both in Jamestown, NY

• And, of course, the EZ Vision control built by Hardinge for the EZ Vision knee mill.

What about a vertical knee mill’s hardware, though? How could that be improved?

Hybrid CNC mills

In business since 1985, Elrod says his creative juices were stirred by what he perceived as a need in industry to create better 3D shapes on a knee mill. He also knew that a lot of you toolroom guys naturally preferred using a manual wheel to get a better handle on the z-axis. These factors drove him to create, patent, and trademark his “Smart-Z” quill drive, which he originally introduced in 1987. He patented his current design in 1999.

Vertical knee mills equipped with his Smart-Zs—“hybrid” mills, as he calls them—can be used in three operating modes: as a three-axis CNC machine; as a two-axis CNC, with the z-axis disconnected from the ballscrew and with z-axis position feedback; and as a manual machine with a three-axis digital readout.

“It allows operators to switch between a servodriven z-axis and a manually operated quill with the same feel they had when the quill was just a manual machine, so power tapping can be accomplished just like a manual mill,” Elrod says.

All a user has to do is disconnect the drive from the ballscrew, articulate the head, and use the machine either as a manual machine or as a CNC machine, while gaining capabilities.

Elrod sells the hardware for his quill drive to other machine manufacturers and retrofitters in addition to using them on his own lines, even on four-axis mills. He says there must be more than 3000 of his units being used in the marketplace today.

A manual option

He’s also promoting it in cyberspace—Elrod recently posted a new video about it on his company’s website. “The video shows people that they’re gaining capabilities using my drive—they’re not losing anything. There’s a scale inside my quill drive that provides feedback when it’s being operated manually. That’s what’s patented. Users always know where they are, whether they’re operating in a manual, two-, or three-axis mode. And there’s also a ‘Smart Stop’ feature. It’s a depth stop provided by a bracket on the quill drive bolted into the unit’s threaded nut.”

He says that after he dreamt up his Smart-Z, his next dream was to offer his invention to the king-of-the-hill, Bridgeport, for use on its EZ-Trak vertical knee mills.

“They had a cantilever drive, but it wasn’t working. So I called them, boxed one up, and I went there. They took their cantilever drive off, put my quill drive on, and after a little while they said, ‘You’ve just saved the EZ-Trak. We’re going to use you,’ and I got the P.O.”

What’s he up to these days? “I’m working on introducing rigid tapping,” he says, “the one thing knee mills can’t do.”

IMM’s RFQ To whom this might concern: I’m John E. B. Goode, the owner and president of Illinois Molds & Molding Co. (IMM) here in Addison. We’re custom molders of consumer products and we also mold some electrical and industrial parts. We’ve got seven molding machines now, ranging from 28-350 tons, and we’re running two shifts, 24/5 (24/7 sometimes). We don’t build any molds—maybe some simple core and cavity inserts to fit into unit frames every now and then—but we do mold repairs in our toolroom. We also cut our own end-of-arm tooling for our robots, and other odds and ends. Business has been pretty good here at IMM for the past couple of years. In fact, I recently added a new 300-ton horizontal press. Right now, though, I’m in the market for a new knee mill for the toolroom. We’ve got a manual Bridgeport that’s seen better days. I think it is still holding up well, but my guys tell me we need a new CNC knee mill. We’re looking for one with a 3-hp head with an R8 taper, and a table size ranging from, say, 9 by 48 to 10 by 54 inches. I’m interested in finding out what you’ve got to offer. Since this would be the first we’ve ever had, I’m as interested in the features and ease-of-use of the control as I am in its ability to cut a part, even a 3D part, with precision and speed. Also, I’d like to know if what you’ve got to offer could be used as a manual machine. I’d like to buy it on standard terms. IMM doesn’t owe the bank any money, and we don’t need it yesterday—a four- to six-week delivery is fine. I’ve got time to do some research. One more thing: Do you supply parts, tech service, and training here in the U.S.? U.S. parts and service are very important to IMM. Very important. We got burnt once on parts and service, and we don’t want something like that happening again. Anyway, what’s the best standard-model, stock machine from your latest lineup that you could recommend, and why? What kinds of options are available for it and how much more, percentage-wise, could I expect to spend for one with the works? I look forward to hearing from you soon. Best regards, John E. B. Goode, president IMM, Addison, IL

Bridgeport Series 1

Bridgeport Series 1

Made in the USA, our Series I can be fit with our EZ Vision for two- or three-axis automated CNC mill work. We can also add on an indexer to automatically index work where the part is held in an indexer horizontally and side work is performed.

Table size: 9-by-48-inch precision-ground and hand-spotted table with dual locks
Spindle speed: Up to 4200 rpm
Spindle taper: R8 (collet capacity up to 3?4 inch)
Number of axes: Can be fit as EZ Vision two- or three-axis automated CNC mill
Motor size: 3-hp, 30-minute duty rate head; 2-hp, continuous
Price: $28,000
Standards: Variable speed (low gear: 60-500 rpm; high gear: 500-4200 rpm) | Up to 36 inches of x-axis table travel; 12 inches of saddle travel; 16 inches of knee travel | 360° ram/turret rotation | Worm and gear controls used for angular head settings—90° left and right, 45° front and back
Options (EZ Vision): Simultaneous three-axis linear or circular interpolation for machining arcs and diagonals | Conversational display and prompts for all program data; operator signals for required actions | Powerful canned milling and drilling cycles for machining circular and rectangular pockets, islands, frame milling, slots, bolt hole patterns, ellipse, and more | Graphics preview feature for program verification | Teach modes for storing manual moves

CNC Masters Supra Deluxe

CNC Masters Supra Deluxe

Your request is definitely one we can fill, Mr. Goode. We have been in business for more than 16 years manufacturing quality, yet competitively priced, CNC milling machines. Our CNC mills are designed with the user in mind who is entering the CNC world for the first time. That is why we have created our CNC mills to be turnkey and user-friendly systems. In fact, we sell all over the world without any onsite training.

Table size: 9 by 49 inches
Spindle speed: Up to 5600 rpm with variable spindle speed computer control—90-2800 rpm for eight speeds
Spindle taper: R8
Number of axes: Three
Motor size: 3 hp
Price: $11,206
Standards: Ease of setup and use | Power Feed one-touch axes alignment—“manual-feel” CNC-based operation, without the need for “cranking the axes” | Direct-drive x and y | One- to two-week delivery
Options: Fourth-axis coordinated motion control | Handheld remote-control joystick | Computer-controlled variable spindle speed | Manual operation
I would highly recommend our Route 66 Task Master Mill with a Centroid CNC controller to you, Mr. Goode. We build a hybrid CNC machine that can be used as three-axis CNC, a two-axis CNC, or a completely manual machine with true three-axis DRO [digital readout] in the manual mode using Elrod’s Smart-Z. Four-axis models are also available.

Elrod Task Master 3 and Task Master 4

Elrod Task Master 3 and Task Master 4

Table size: 10 by 50 inches, Task Master 3; 10 by 54 inches, Task Master 4 (pictured)
Spindle speed: 4250-5000 rpm
Spindle taper: R8 and #40
Number of axes: Shipped as three-axis; can be used as two-axis; can also be upgraded to simultaneous four-axis
Motor size: 3 hp for R8; 5 hp for #40
Prices: $24,500 for Standard Route 66 Task Master 3; $29,800 for Standard Route 66 Task Master 4
Standards: The head can be trammed into position | The z-axis can be disconnected and used manually with z-axis feedback, if required; an integrated quill stop can be included on the z-axis quill drive; all three axes are laser-mapped for increased accuracy | The Quill Drive’s mounting does not interfere with the tramming of the head | The control is easy to understand and program | The machine can be used either with 220V/three-phase, or 220V/single-phase operation.
Options: DXF import; unlimited file sizes | Rigid tapping | Digitizing feature (for reverse engineering) | Automated tool setter | Multiple work coordinates, subroutine and macro calling; mirror and scaling; coordinate system rotate (enables user to line the machine to the part instead of indicating the part to the machine

Lagun KMC 717

Lagun KMC 717

Thank you for sending Republic Lagun your RFQ, John. All of our CNC knee mills are laser-verified and ballbar tested, and provide .0004-inch positioning accuracy over full table travel and ±.0001-inch repeatability with ±.0001-inch resolution. They’re also built for easy loading and unloading of workpieces. Engineering is European and machines are built with imported European steel.

Table size: 11 by 58 inches
Spindle speed: Up to 4250 rpm
Spindle taper: MMT #40
Number of axes: Three (fourth optional)
Motor size: 7.5 hp
Price: $53,870 (with Fanuc control)
Standards: Very large spindle quill with 7 inches of CNC-controlled travel | Large 11-by-58-inch table | Hardened and ground ways | Special cross travel of 17 inches with a knee support for working with heavy molds | Rigid ram for very heavy milling cuts
Options: All CNC controls are available: Fanuc, Dynapath, Fagor, and others | Fourth-axis rotary or indexing attachments | Electronic variable-speed head | Electrics in NEMA enclosure | Bellows-design way covers

All Summit SmartCut models are designed to be rugged and easy to use, Mr. Goode, and they’re equipped with independent servos on each axis sized to allow maximum material removal, while providing the quick response you need for smooth transition while you’re performing simultaneous cuts. And they’re versatile, providing DRO when manually worked. Click here, to download (pdf) the full quote.

Summit Machine Tool SmartCut EVS 350B

Summit Machine Tool SmartCut EVS 350B

Table size: 10 by 54 inches
Spindle speed: Up to 4300 rpm
Spindle taper: R8
Number of axes: Three
Motor size: 3 hp
Price: $27,995 (plus $2500 installation assistance, including startup and basic operator training)
Standards: Conveniently located Fagor 8040 MC CNC control | Heavy Meehanite cast iron construction | Huge box ways on knee | Double table locks and wipers on saddle and column | Built-in coolant system | Automatic way lubrication | Complete electrics with low-voltage controls
Options: Fourth axis | Rotary tables

Knee mill anatomy If you don’t spend too much time in the toolroom, you can surprise the folks back there with your detailed knowledge after studying this graphic. It comes from Virtual Machine Shop. VMS was created by volunteers from industry and academia. Its information and services are offered online for free. • The head (drive) is that part of the drive system that transforms electrical power from a motor to mechanical power in the spindle. The drive system also allows the machinist to change the speed of the spindle (rpm) and therefore the cutting tool. • The quill moves vertically in the head and contains the spindle in which cutting tools are installed. • The quill feed hand wheel moves the quill up and down within the head, as does the quill feed lever. • The knee moves up and down by sliding on ways that are parallel to the column. • The saddle sits on the knee and allows translation of the worktable. Sitting on the base is the column, whose main function is to hold the turret. The turret allows the milling head to be rotated around the column’s center. • The overarm (ram) slides on the turret and allows the milling head to be repositioned over the table. • The longitudinal traverse hand wheel moves the worktable to the left and right, the cross traverse hand wheel moves the worktable in and out, and the vertical movement crank moves the knee, saddle, and worktable up and down in unison.

Web-exclusive: 20 questions Our guest, Dwayne Elrod, says that if you're shopping for a new CNC knee mill, while the size of the machine can be important, the real specifics you should be asking about include the following: 1. What are the control features? 2. Can it cut a 3D part with precision and speed? 3. What is the processing speed of the control when cutting a 3D part? 4. Can it import CAD data (DXF) for the onboard conversational programming? 5. Can it work in two-axis as well as three-axis modes? 6. Can it be used as a manual machine with hand wheels and provide capabilitites to use the quill manually? 7. Is the machine built with excellent CNC mounting hardware, such as heavy-duty x-y brackets? 8. Is the machine equipped with a reliable quill drive that is capable of tramming the head without misaligning the quill drive? 9. Is there a stop on the quill when the z-axis drive is disconnected? 10. Does the control use standard Fanuc Style G-codes so a file can be loaded from an offline CAM system? 11. Does the control use Multiple Work Coordinates G54-G59, Subroutines and Macros G65 and M98, Mirror/Scaling G50, and G51, Coordinate System Rotate? 12. What is the file size capability of the control for large 3D files? 13. Can the control thread mill? 14. How does the operator import a G code file from an offline system? By USB, or by floppy? 15. Does the control have network connectivity? 16. Is there a basic training DVD or CD for operating the control? 17. How is the support after the sale resolved? 18. Does the machine have programmable spindle speeds? 19. Is the machine's spindle inverter driven or is it standard induction with mechanical vari-speed pulleys? 20. How much does it cost?

Web-exclusive: A need for speed? John Gravelle, president of custom molder Mar-Lee Cos. (Fitchburg, MA; www.mar-leecompanies.com) started out as a moldmaker in 1972. “You use a knee mill when you need something done in a hurry, something like a one-man job that's not going to go through a whole, long, involved process. There's definitely still a need for that type of equipment.” Gravelle says a good knee mill needs a good spindle. “You need a larger, heavier spindle, or else your cutters won't run true. That's the biggest part of it.” One thing he says you may not need, though, is a superhigh-speed spindle. “I've not yet seen the need for working with a high-speed spindle-something over 6000 rpm. If you go too fast-say, 40,000 rpm-you risk deflection. With slower spindle speeds, it's not that big of an issue.”

Web-exclusive: Knee-mill memories Steve Johnson, maintenance systems manager at Progressive Components (Wauconda, IL; www.procomps.com), is the creator of MoldTrax 4.0, a brand-new mold maintenance tracking software program designed to be easy to use and understand. A six-year jet mechanic for the U.S. Navy, Johnson then put in 25 years as a toolbuilder for a major medical molder. “I remember when CNC controls for vertical knee mills were just taking off,” Johnson says. “They just had digital readouts, variable speed, and an auto-course feeder. They've changed a lot over the years, but those mills are still a must in any shop.”

Web-exclusive: Keep it simple Chris Serafin heads up a 10-man shop called New England Tool & Microweld Inc. (Johnston, RI; www.newenglandmicroweld.com) that provides a wide variety of services, everything from new mold construction to contract maintenance, and revision and repairs of exiting molds. He's a got a 5-hp, 12-by-50-inch Sharp mill with an Acu-Rite control. “CNC knee mills today are a little more user friendly than they used to be,” Serafin says. “My guys are, well, older guys. They don't even want to touch a computer. We need something to close that gap. We're trying to find a happy medium.” “There are some controls out there that are just too complex. Others are just too simple and can't do what we want to do. “If I were in the market, I'd be looking for a machine that could do complex things with the least amount of input—ideally, a mill with a two keypunch control. We don't have a lot of time to do a lot of programming. The simpler the better. We'd like one designed for a moldmaker, not for an engineer.”

Contact information Acu-Rite Cos. Inc. | www.acu-rite.com Anilam | www.anilam.com Bridgeport | www.bpt.com Centroid Inc. | www.centroidinc.com CNC Masters Inc. | www.cncmasters.com Elrod Machine & Mfg. Inc. | www.elrodmachine.com Fagor Automation | www.fagor-automation.com Hardinge Inc. | www.hardingeus.com Heidenhain Corp. | www.heidenhain.com Republic Lagun Machine Tool Co. | www.lagun.com Summit Machine Tool Mfg. Corp. | www.summitmachinetool.com Virtual Machine Shop | www.jjjtrain.com/vms/