A more complex method for tilting is with an automatic tilting head, that tilts the nozzle during machining. In most cases, the main purpose of the multi-axis cutting head is for taper removal to make perfectly straight edges in the part for high-precision work. Multi-axis heads like this can also be used to purposely introduce small angles into the part as well (but things get a bit more complex when this is desired.)
A programmable 5-axis tilting head.
(Right) Waterjet part with virtually no taper. On the left is a picture of the same part set vertically next to a 123 block on a surface plate, demonstrating its lack of taper.
Another pair of parts cut with a tilting head: 0.5″ (1.2 cm) brass bicycle and 0.5″ (1.2 cm) stainless steel test part.
Computer controlled tilting cutting heads can offer a significant improvement in cutting precision over non-tilting cutting heads. The big advantage is that you can make a virtually taper-free part, without having to slow the cutting down. It’s also possible to cut almost taper free parts without tilting. However, it takes a much more careful setup, and it also takes slowing the machine way down. The end results are not quite as good as when cut with tilting, and the part is way more expensive to make, but if you rarely care about taper, then maybe a no-tilt strategy is fine.
A waterjet cutting Teflon
The above picture shows a lot of things:
- In the foreground, there is a mechanical drill mounted to the same motion system as the nozzle. This is used primarily to pre-drill start holes for cutting. Pre-drilling is almost never required, but is useful when cutting materials that don’t pierce well, such as some laminates that otherwise might blister. Although this picture shows Teflon® being cut, the drill was not used in this case, as Teflon cuts nicely without it.)
- In the background is a tilting cutting head for taper removal. In this setup with both accessories attached, the drill drills, and the cutting head then moves over to do the cutting.
- Some Teflon plastic material, and some parts cut from it. Notice that all of the parts are linked together with short bridges so it’s one single part that is cut, and then the small pieces are cut off with wire cutters or similar later.
- Waterjet brick supporting the material. This is useful to use when the splash-back from the slats might mar the material (in this case, to prevent the Teflon from getting scratched up). It is also useful for supporting the material when cutting tiny parts that might otherwise fall through the slats. In this particular machine setup, the waterjet brick is mounted on half of the machine, while traditional slats are mounted on the other side.
- Aluminum “square” that the Teflon is pushed against. By cutting a square like this from a sheet of aluminum bolted to the table, it is possible to precisely locate parts for secondary machining. Because the machine was used to cut the square, it is assured that the square is indeed “square” to the machine, and the corner of the square’s position is known exactly, so that it can be used as a reference point.
- Notice the Quick-Grip clamp and weight used to fixture the materials. This is a pretty typical fixturing setup.
Another picture of a tilting cutting head with a splash guard is in front
Programmable tilting heads are excellent for making precision parts, because taper is almost completely eliminated. Because the head can tilt in all directions (including towards the operator and towards the side of the catcher tank), the tilting movement of the head may be restricted for safety reasons. If a part made with a given material has a lot of taper, it may not be possible to remove it all using the automatic tilting head.
You do not have to use a tilting cutting head to make precision parts. You can make nearly taper-free parts without tilting by simply slowing the cutting down. However, it is usually necessary to slow the cutting down a lot to get rid of taper in many parts, so the tilting head allows you to make the same part in less time.
Control of the tilting head is handled by software, as it can be quite complex to calculate the position and angle of the head for the entire tool path. As a result, it is easy to use a tilting head. With most software, there is simply a check box that turns on the tilting calculations.
The tilting head won’t completely eliminate taper for all parts. In very thick parts, where barrel taper can occur, the tilting will only get rid of some of the taper, but not the barrel.
When cutting over waterjet brick, tilting the head will cause the brick to wear out faster than usual because the stream is hitting the brick in the sides.
One of the easiest ways to create angled cuts is by simply tilting the nozzle to the desired angle. The advantage of this is that it is cheap and easy to do. No special programming is required. A disadvantage is that significant more splash will occur, since the nozzle is now pointing diagonally across the catcher tank. You also cannot change the tilt for different features of the part without having to stop and readjust the nozzle angle.
If you modify your machine to do this kind of work, be sure to consider the splash. You should aim the nozzle so that the splash shoots towards the back of the machine, and away from you. Also, cut a nozzle guard from a piece of pipe, that is at an angle, so that the bottom of the pipe is flush with the surface to cut. And, as always, wear eye protection.
Also, remember that the jet is a lot more powerful than it looks. When you tilt it sideways, it shoots sideways, and ricochets sideways. Take extra precautions with this in mind—don’t cut too close to the edge of the catcher tank. Don’t cut yourself to pieces, and don’t cut your machine to pieces either.
Below are some pictures of some blades cut with a fixed tilt waterjet.
Blades with tapered cuts in stainless steel, and the one with the blue background is in M2 high speed steel. A typical part like this would take perhaps 2-5 minutes to cut depending on the complexity of the shape. With precision waterjet machines, little or no additional grinding is needed.
Close-up of the edge of the blade.
Special mounting for the nozzle to allow it to tilt
You can get a special mounting for your nozzle which makes it easy to tilt the nozzle. All you do is loosen a nut , and the nozzle is manually tilted to the desired angle, then the nut is retightened. Depending on how the plumbing for the high pressure tubing is handled, it may need some adjusting as well. The big red plug in the side of this assembly shown above is a plastic plug to prevent dirt from falling into the nozzle assembly, since the plumbing is not hooked up in this picture.