Compass cutting warped material

The Importance of Standoff Height, Especially with Bevel Cutting

Standoff height, the distance between the tip of the mixing tube and the material you are cutting, is important when cutting parts on a waterjet. In a previous blog I provided recommendations for proper standoff height. In general, stand off height should be about 0.100” (2.5 mm), or as thick as a dime. When your jet is perpendicular to your part, straight up and down, then raising the standoff will increase noise, mess and round the top edge of the part. You will lose a little cut power as well.

It’s important to maintain stand off under conventional waterjet cutting.

How Waterjets Work

Understanding Waterjet Motion Equipment

As we know, waterjets cut via a supersonic stream. Although there are hand held waterjets used to remove paint, most waterjets are typically moved around with some type of motion equipment.

Waterjets are rather easy to plumb to a machine using elbows, T’s, and other fittings common, in concept, to plumbing a house. Rather than using PVC pipe, we use stainless steel lines of 1/4″ to 9/16″ outside diameter and stainless steel fittings. And motion can be obtained by swivel joints or simply by making the stainless steel line long enough to allow for flexing within the elastic deformation range. Backthrust on the machine is rather small (under 20 pounds [9 kg] for most waterjet applications) even though we are pressurizing the water to very high levels (up to 94,000 psi, or 6480 bar) because not very much water is used (approximately 1 gallon per minute).

Here is a high level overview of the motion equipment that moves around the waterjets.

Waterjet 101 Waterjet Technology Overview