Glastonbury Engraving, Glastonbury, Connecticut, designed and built a unique router that efficiently produces custom-engraved laminated control panels in very small quantities to meet customer requirements. The new machine has allowed the firm to significantly reduce the cost of producing control panels, primarily for converting equipment, with, for example, a flow diagram of the production equipment engraved upon it. Despite its one of a kind design, the machine was relatively inexpensive because it was built completely with standard components. The most unique design feature is the use of a crossed roller slide to provide z-axis travel in order to maintain a constant depth of cut despite possible material distortion.
Since 1971, Glastonbury engraving has been a leading supplier of stainless steel, anodized, painted, and its own Tuf-Tex and Alumatex panels to the printing industry, paper converting industry, plastic extrusion industry and many others. The firm specializes in providing one-of-a-kind solutions to meet its customers’ special needs. Many of these panels are built from Tuf-Tex, a new laminated, abuse-resistant panel designed to replace anodized, painted, photoetched, silk-screened and conventionally engraved control panels. This panel material features a .025 thermoset resin top laminate and bottom metal subpanel. Glastonbury engraves permanent graphics, including multi-colored graphic inlays and dry erase sections, in solid multicolor resin laminate.
Custom panels at competitive prices
Chuck McKinney, Plant Engineer, for Glastonbury, said that the firm has worked hard over the last several years to develop the equipment and processes needed to produce custom-built panels while remaining cost competitive with off-the-shelf panels built in much larger quantities by competitors. “The ability to provide a custom panel for a competitive price with a fast turnaround is a major plus in this business,” McKinney said. “This makes it possible for developers of converting equipment and other machinery to add intelligence to their panels by providing diagrams and text that make their machines easier to operate. What our customers want is the ability to produce custom panels with a wide range of complicated designs at a price that is very close to plain standard panels. To complicate the situation, they don’t want to keep a lot of inventory on the shelf. To meet this requirement, we need to be able to efficiently produce panels in small quantities, often only one at a time. Yet, the panels need to match up perfectly with those that we have produced in the past. Clearly, the only possible way to do this is through CNC machining.”
But a traditional CNC machining center would be a very poor fit for our needs,” McKinney pointed out. “The main problem was that we would have had to pay a huge amount of money, probably a minimum of $100,000, for a machining center with a working area big enough to handle our larger panels. But this type of machine really would have been overkill for our work because it is designed to handle much heavier machining tasks. Another concern was that the laminate materials used to produce panels have a tendency to exhibit some distortion when they are laid out on a table for cutting. The tools used for engraving have angled sides which means that if the workpiece lifts off the table both the width and depth of cut will be too great. We needed some method for detect the location of the material and adjust the position of the tool.”
Need to re-use existing programs
To add another complicating factor, Glastonbury Engraving has been using several machines that it purchased a number of years ago for this task. These machines use a special controller that was orphaned when its manufacturer went out of business. Glastonbury engineers had created thousands of CNC programs used to drive this machine to produce custom panels for its customers. A high proportion of these panels were for machines that were still being produced by customers. McKinney wanted to avoid at all costs having to reprogram all of these panels. So he needed a machine with a controller that could read the proprietary format used by the old controller.
Clearly, the only way to meet all of these requirement was to build its own machine. But McKinney wanted to minimize design time by using off-the-shelf components wherever possible. He made a major step forward when he identified a base table from Techno-Isel, New Hyde Park, New York, that provides a work area of 4 feet by 8 feet, sufficient to meet his requirements, at a very attractive price. The Techno table features a positioning accuracy of +1 mm in 300 mm, providing the ability to produce parts with tight tolerances. Its use of anti-backlash ball screws, for example, ensures play-free motion. These screws have excellent power transmission due to the rolling ball contract between the nut and screws. This type of contact ensures low friction, low wear, and long life.”
McKinney himself designed the control system for the new machine. He started by porting over the control system from the old machine in order to provide the capability to read the existing programs. He added a number of new features such as the ability to obtain the basic cutter geometry from an AutoCAD file while using special fonts designed by the firm to provide superior text. McKinney interfaced the card with servo motors that he had picked specially for the task.
Challenge of maintaining width of cut
The greatest challenge of all was providing the ability for the machine with the ability to automatically adapt the height of the workpiece to maintain the depth of cut constant regardless of material distortions. McKinney had seen engraving machines with a nose cone on the tool and a free traveling z-axis that allowed the tool to ride on the workpiece. His primary obstacle was finding a linear motion device that would support the weight of the spindle, resist cutting forces and provide accurate but very low friction spindle motion in the z-axis.
To select the device, McKinney used a CD-ROM catalog provided by Del-Tron Precision, Inc., Bethel, Connecticut. The CD-ROM contains a textual description of each linear motion device produced by Del-Tron, including the applications for which it is intended, complete dimensional information and specifications such as the accuracy of each device and the loads that it is capable of withstanding. An important difference in the new CD-ROM catalog is the ability to search the CD-ROM for a particular part number, type of slide, application, etc. Rather than having to leaf through a thick paper book, the user is immediately transported to the information of interest. Another key difference is that the CD-ROM includes a fully dimensioned drawing of each linear motion device in the popular DXF format. This means that once the user has selected the part for their application, they can simply import the drawing into their CAD system.
Selecting slide on CD-ROM
“The CD-ROM made easy to pick out the right slide,” McKinney said. “I knew the mass and size of the spindle and the dimensions of the slidehead and bracket that I had designed to mount the slide. I found a crossed roller slide with 6 inch travel and a 2300 pound capacity that met all of my requirements.” Crossed roller slides physically resemble ball slides except for the bearing design. Specifically, each slide is comprised of an aluminum carriage straddling an aluminum base. Using a bearing system containing cylindrical steel rollers, the carriage glides, almost friction-free, over the base. The rollers, alternately crisscrossed with each other, move between a set of four, partially flat, parallel, smooth rods on each side of the base. The rollers share a larger contact surface with the rods as compared to the point contact of steel balls. This bearing design allows crossed roller slides to carry larger loads and absorb greater load impacts than equivalent size ball slides. The carriage and base is made of aluminum while hardened steel rods and rollers and stainless steel end caps are used.
Del-Tron crossed roller slides met another important requirement of this application – very high accuracy. They provide straight line accuracy of 0.0001 inch per inch of travel when measuring the line of travel to a master straight edge, using a gauge or indicator mounted on the slide. Positional repeatability of the slides is 0.0001 inch. The coefficient of friction of these devices is only 0.003. At rated load capacity and moderate speeds, expected life is 10 million inches of travel. The expected life at one half the rated load is 100 million inches.
“This machine has turned out to be the best we have ever seen for panel engraving,” McKinney said. “We can produce whatever type of panel the customer wants with very low setup time simply by loading in a new program. Customers typically send us their designs in AutoCAD files which means we only have to spend a few minutes programming each design. The size of the new machine and power of its control system means that we can now produce very complicated custom panels at only a very small premium to standard designs. For example, we recently did a panel with a flow chart that shows the entire web path of the converting machine in multiple colors engraved on the console.”
|
