October 10, 2006
Many machine components formerly made with conventional machining techniques now can be made easily and cost-effectively with abrasive waterjet cutting. This article discusses some of these components. It also gives examples of abrasive waterjet-produced signs and labels that can be used to enhance your products.
Lathe Screw Cutting Drive Train
An article published previously on thefabricator.com, How one shop benefited from abrasive waterjet technology, presented novel construction techniques that can be implemented effectively with an abrasive waterjet machine to lower the costs of building fabricated structures.
But abrasive waterjet machines can be used to make components, too, such as gears and parts with gear segments; sprockets and chains; cams; ratchets; springs and flexures; keys and keyways; wrenches; hand wheels; clamps; brake disks; and even signs and labels that might be added to a structure to form a completed machine. These components, which formerly may have been made using conventional machining techniques, now can be made cost-effectively in a fabrication shop with an abrasive waterjet.
The key to producing many of these machine elements successfully is using precision waterjet equipment. Many components also require the taper-free cutting discussed in the article Improving waterjet cutting precision by eliminating taper.
Since most modern abrasive waterjet machines make parts directly from a CAD file (usually a 2-D dxf file), the ease of making the part depends on how easy it is to make the CAD file. Many good CAD programs are available. This article presents design ideas only and is not intended to promote a particular CAD program.
An abrasive waterjet usually is not thought of as a gear-making machine, but a gear tooth is just one particular shape that can be made easily with an abrasive waterjet. A precision abrasive waterjet often can stay within 0.001 in. of the desired contour, and an ordinary machine can stay within 0.005 in. For many applications this tolerance is sufficient.
Closeup of Abrasive Jet Gear
Planetary Gear Set
for Lapping Machine
Figures 1and 2show a gear used in the lead screw drive train of a screw cutting lathe that was made in about 10 minutes with an abrasive waterjet. This custom gear was needed to achieve a 1/2-in. pitch for a spring winding application. It ran as smoothly and quietly as the other gears in the train. Note in Figure 2 that the keyway and close-fitting bore also were made with the abrasive waterjet.
Winch Gearing with
Ratchet and Pawl
Figure 3is a planetary gear system in which the round holes in the planets are used to carry workpieces in a lapping machine. The total time to make the entire system in 1/8-in. steel was less than 40 minutes.
Figure 4is an internal gear driven by a spur gear for an application in a winch. In this case, the key is built into the spur gear rather than using a keyway. Note that the ratchet and pawl also are abrasive waterjet machine-made parts.
Even odd-shaped gears can be made by an abrasive waterjet, which alsocan form racks and mating gear sectors in a manner that easily facilitates a linear motion by pulling a lever.
Ordinarily you would not make your own chain, but what if you wanted to lift 300 tons? You then would be forced to make your own. Links in the chain in shown in Figure 5were made with an abrasive waterjet and assembled into a chain that can lift a 300-ton object.
Chain Links Lifting 300 Tons
It would be more common to make a sprocket and buy the chain. Sprocket geometry can be found in Machinery's Handbook, and it is quite easy to follow the specifications, draw the desired sprocket, and produce it with an abrasive waterjet.
With the advent of low-cost servo drives and control systems, cams are used less than they were in earlier times, but they still provide a low-cost means of making particular motion profiles. Cams also can be used as wedging mechanisms for locking movable elements in place.
Cams can be made very quickly on an abrasive waterjet. The major portion of the work is determining the desired cam shape. Once the shape is known, making the cam is as simple as loading the CAD file into the machine and pressing go[START?].
Figure 6shows a cam ready to be cut according to the function:
R = 2 + Sin(Theta)
A hole with a keyway has been added so the cam can provide a reciprocating motion.
Two types of springs can be made on an abrasive waterjet. One type flexes normal to the plane of the X-Y table, and the other flexes parallel to it. Figure 7shows a spiral spring typically made from a thin sheet of heat-treated spring stock. The spring is held on its outer diameter, and the moving member is attached to the central hole. The spring is very rigid in the radial direction, but quite flexible in the axial direction. If two such springs are placed a short distance apart, one above the other, they provide a quite good flexural bearing for limited motion.
Figure 8shows a flexural spring in which the motion is parallel to the X-Y plane. A motor and gearbox are mounted in the circular hole, and the assembly is preloaded against a rail to provide a friction drive. The flexure provides a spring force of about 500 lbs. to hold the drive wheel firmly against the rail.
Flexure for Preloading a Drive Wheel
Electrical Control Panel
Electrical panels often have odd-shaped holes that are difficult to make without custom punches. The abrasive waterjet is a good tool for cutting these holes directly from a CAD file. No dimensional drawing is required. Figure 9shows a flat panel.
By placing a shield to deflect the jet, you can cut holes in the sides of an electrical box as well (see Figure 10).
Electrical Control Box
Abrasive waterjet cutting can be used to make myriad machine elements, including snap rings; custom wrenches; shims from laminated stock; heat exchanger tube headers; etched, hardened jaws; exhaust header plates; and rubber gaskets.
Instructional or Name Plate
Signs normally are not thought of as machine components, yet they serve important purposes. Here are some signage ideas that can be achieved with an abrasive waterjet:
A precise and versatile cutting tool, an abrasive waterjet can be used cost-effectively to make many components formerly made by other means.