Waterjet Cutting: Selecting the Right Surface Finish and Taper for the Job

Choosing th correct surface finish and taper is critical to determining the cost of a waterjet-cut part. In fact, the cost can be greatly reduced if a lower-quality cut is allowable. This depends, of course, on the tolerances and edge quality that are required. Please consult a SMC Sales rep to determine which surface finish is best for your application.

	Super Quality Premium surface features a smooth, sandblasted appearance. A Medium Commercial finish acceptable for many net parts.
	Quality Second-highest quality surface finish. Smooth appearance with slight striations.
	Medium Quality A medium quality cut with detectable striations. Acceptable when tool marks are not objectionable.
	Separation Heavy striations are obvious, but with no deep, grooved edges.
	Rough Separation Separation cut with rough, low- grade surface finish with severe striations and grooved edges.

Finish: A Combination of Speed and Cost
While a premium-quality cut often achieves net-shaped parts that require no secondary machining, a lower-grade cut may be preferable. In some cases, a rougher surface finish is more desirable, especially with parts that do not require close tolerances such as those that are roughed out prior to final machining.

Finding Allowable Taper
Besides surface finish, another important consideration in determining the cost of waterjet cutting is allowable taper. Taper is the difference between the top profile fo the cut and the bottom profile. Like surface finish, taper also depends on the cutting speed - the faster the cutting, the larger the taper will be. Generally, lower tolerances permit faster movement of the cutting heads and less machining time. Higher accuracy requires slower cutting.

When the waterjet cuts through material quickly, the cutting stream leaves a V-shaped taper since it cannot completely eliminate the material. As cutting is slowed to optimal speed, the taper will be reduced until both sides of the cut are parallel or nearly parallel. Generally, the taper on a super quality cut is 0.003" - .0005" on each side. As cutting is slowed further, the stream widens at the bottom, resulting in reverse taper.

	Normal Taper Caused by cutting fast. Minimal Taper Caused by using optimal speed. Reverse Taper Caused by cutting slow.

 

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