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Head movement adds Z-axis control, travel to knee mills.

Milltronics has recently introduced a new concept in third axis control of a knee-type machine. A servo box called the Millslide accessory is installed behind the head. It leaves the 5" of manual quill travel intact, but adds 7" of head servo control travel. The operator can therefore choose two- or three-axes operation.

Easy-to-use, relatively inexpensive two- and three-axis controls are giving many knee mills a new lease on life ("Knee mills cut fine figures with CNC controls," T&P, April 1993).

One of the difficulties with adapting three-axis control to knee mills has been bringing the third axis--the up-and-down movement of the quill--under CNC control, says Timothy Rashleger, operations manager at Milltronics Manufacturing Co, Chanhassen, MN. "People have tried a lot of different schemes, including mechanically turning the crank, putting a gear drive on the quill handle, and putting a ballscrew in front of the head." Not only do these designs sometimes suffer from strength and alignment problems, but they all have one thing in common, says Mr Rashleger: they all restrict, to varying degrees, the ability to manually operate the quill.

Enter Milltronics. "We wanted to make knee mills into three-axis machines that are very user-friendly in the toolroom, where you're not running high production," Mr Rashleger tells T&P. "That means we wanted to be able to crank the third axis manually somehow, because that's what's neat about the two-axis machines."

What the company came up with is a system called Millslide, which provides a way to move the entire machine head up and down while leaving all the handles, depth stops, and other manual accoutrements intact. This approach lets operators use the machine in a variety of modes: full manual; two-axis, with manual Z-axis control; three-axis computer control; and combined CNC and manual operation of the Z axis. "People see the whole head going up and down, and it kind of blows a guy's mind who has been working on these machines all his life," says Mr Rashleger.

The Millslide system mounts behind the head, using a ballscrew to move the head up and down for up to 7" of Z-axis travel. It also allows full use of the 5" of quill travel that is standard on most knee mills, for total Z-axis movement of up to 12". "The head only moves if the program has Z-axis information in it," says Mr Rashleger. "Even if the program has Z-axis information, that doesn't preclude manual control of the mill."

As an example of how combined CNC and manual operation might work, Mr Rashleger cites drilling a hole 10" deep. "The operator could start drilling, and when he gets 6" deep, he could have the head move all the way to the top of the slide, then he could pull the quill down 4" and finish the hole. From a practical point of view, I'm not sure how much they'll actually go back and forth like that, but toolroom guys tend to be very innovative," he says.

One thing he does expect to see commonly done is using the Millslide system to essentially preset tools. "R8 collet systems don't give you preset tooling. So I might use the quill to set my Z length or touch my tool off on the top of a part, then I'd lock the quill there and use the servo for Z-axis movement. That would be a quick way to pick a reference point, lock the quill, and then let the servo do its work," he says.

The Millslide system servo-motor holds the slide in place when the head movement feature is not in use. A ballscrew with linear ways under heavy preload provides good strength and stiffness with minimal degradation of machine performance, says Mr Rashleger. The way technology is basically the same as that used in Milltronics' and other manufacturers' low-end machining centers. Patents are pending on the design.

One machine capability that is essentially lost is tilting of the head side-to-side and backward; the head can still be tilted forward. Mr Rashleger emphasizes that enough side-to-side tilting ability is maintained to square the head with the table.

Milltronics sells its Partner 00 knee mill equipped with the Millslide two-axis system for $21,980; Z-axis control can be added for an additional $4000. The company also is doing a brisk retrofit business, adding the system to about one machine a day. A two-axis retrofit including installation runs $12,595; the Z-axis control adds $5000. Many purchasers of new knee mills are having the machines drop-shipped directly to Milltronics for installation of the Millslide system, says Mr Rashleger. He also points out that the Z-axis control also can be added at any time after installation of the two-axis control system. "You can start by buying just two axes, then add the third axis in the field later. It's all prewired."

For information on the Millslide system from Milltronics Manufacturing Co, Chanhassen, MN, circle 311.
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Title Annotation:Management Update
Publication:Tooling & Production
Date:Jun 1, 1993
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