Waterjets are superbly effective cutting tools. But under some circumstances, they can create what’s called taper. This means that the edges of the newly cut material are uneven rather than straight. Fortunately, it’s easy to control waterjet taper.
The factors causing taper
A number of factors can cause taper. They include:
- distance of nozzle from material
- quality of abrasive used
- material hardness: harder materials show the least taper
- material thickness: thinner materials exhibit more taper than thicker ones
- cutting speed: nozzles that move too quickly or too slowly can create taper
- jet quality: the more focused the nozzle, the less taper
How to minimize taper
The first thing you can do to control taper is to use a small nozzle with a .01” (.25 mm) jewel and a .02” (.51 mm) mixing tube. You should also use the best quality abrasive you can and the larger grit size that will fit the nozzle without plugging it up.
Just before you start, check to see how low you can get the nozzle to the material. Nozzles set lower will create less taper. Consider pre-punching the starting holes with a pass at a higher stand-off. Then lower the nozzle to do the rest of the cutting.
When you do finally get to cutting, work slowly. Be aware, though, that if you go too slowly, you may get the taper effect you were looking to avoid.
You can also try to design your object to minimize taper impact. Know in advance that objects cut on a waterjet will tend to exhibit a few thousandths of an inch of taper.
So if you’re cutting gears, you could cut every other gear upside down. That’s because when they mesh together, the tapers will cancel each other out. This inversion method can also be useful when you need to embed two objects into each other as in the case of marble inlays.
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