New technology, longer-life mixing tubes, diamond orifices, CAD / CAM software and easy-to-use touch screen controllers are all making it possible for waterjets to cut better parts the first time.

Yet no matter how sophisticated endeavors are to make waterjet cutting easy, you can’t get away from the fact that if you don’t hear that “hissing sound” coming from the waterjet, you aren’t making any money! And what it takes to get that “hissing sound” tends to be founded solely on the basic principles of how long it takes to go from completing one job and starting to cut the next. In other words, how efficiently are you loading and unloading a job onto the waterjet table?

Manufacturers of waterjets have focused a great deal on increasing the accuracy of the motion part of waterjets over the years. Companies considering which type of CNC equipment to purchase next will ask questions about this accuracy as well as about tolerances. Questions about the type of motion system, such as ball screw, rack and pinion or belt drive, along with accuracy statements, ballbar readings, laser inferometer printouts and calibration details must be addressed prior to selecting a waterjet. However, potential and current operators often overlook questions about how to secure the part they’re preparing to cut, and how it will be clamped down and positioned on the table.

You must go a step further in your endeavor to run an efficient waterjet business. An often-overlooked key to the success of running a waterjet job shop is improving the ability to quickly load and unload a job onto your waterjet table. You must assess how easy it is to clamp a part of any shape, anywhere on the table, and have peace of mind that it is flat, will not vibrate, and can be removed or replaced in seconds.

Slats have been used as the traditional method of supporting parts on waterjet tables. Operators have found that slats do not fit tightly into the table so they tend to vibrate when parts are cut. The way in which slats are secured into and taken out of the tank contributes to their inadequacy. Over time you may find that abrasive fills in some of the slots and can erode the openings. This will lead to varying heights of the slats thus large parts would no longer lay flat. So although your waterjet may be able to hold extremely tight tolerances these may be lost if there is movement of the slats.

As an alternative to slats the ideal support system would consist of 4” or 5” deep grates made out of a thin gauge material and are box shaped with an interlocking pattern. It is easy to understand why this has not been done before, as thin 4” or 5” strips of steel tend to be floppy and want to fall over. However, if each intersection is securely welded the grate will retain its inherent strength even when some of the welds are cut free by the waterjet. The space within each box would allow enough space to access the tank if need be.

No matter whether slats or grates are used to support a part, waterjet cutting is so powerful you can count on the support underneath being cut up to some extent. The thicker the material being cut, the slower the cut speed, which results in deeper damage to the supporting material. It is possible to limit this damage by applying certain principles of waterjet cutting to the way a support system is designed and built. The following information focuses on the advantages of the more stable and versatile grate system.

Normally cuts will not go much deeper than 2” into the underlying support material so it is important that grates are deep enough to resist being cut all the way through. Typically grates should be at least 4” deep. On one occasion when hired as a consultant, Richard Ward, President of WARDJet, Inc., Tallmadge, Ohio, witnessed the first part being cut on a waterjet that had 1.5” deep galvanized steel floor grates used as the support system. Prior to the cutting of the first part on the machine he commented that the grates did not appear deep enough. Only when the grates were cut all the way through and the entire part fell into the tank did the message “sink in”.

The belief that a wider slat system will perform better and last longer is not necessarily true. In fact it is proven that the wider the contact surface of a slat presented to the stream, the more of a bite the stream takes out of the slat. Another undesirable point is that the wider surface tends to deflect and kick the stream back into the underside of the part being cut. On harder materials this is not an issue, but on softer aluminum, phoenalics, acrylics or materials with polished surfaces, the kickback damage can be substantial. In many instances the kickback is seen to line up with where the parts were resting on the slats.

Purchasing grates that consist of thinner gauge material addresses both of these subjects. Typically the stream has an arc trailing behind the entry point that digs into the support material. When the grate is thin, the arc tends to jump over the grate rather then dig into it and cut deep. It also stands to reason that with a much narrower surface presented to the stream, kickback is vastly reduced. This also negates the need to have sacrificial layers of material between the grates and the underside of your material, like you would need when cutting on slats. For example, this can specifically benefit aerospace companies who waterjet cut carbon fiber sheet. Damage to the carbon fiber sheeting can be almost eliminated when using the box style grates.

When the waterjet operator knows that the grate will not move during cutting and that it is possible to place any part anywhere on the table and clamp it into position there is confidence that the needed tolerances will be achieved. There is no need to try to secure the material to be cut to the front, sides or walls of the tank in order to gain stability. This frees you up to clamp anywhere on the grating system.

The clamping method with the grating system is completely different than with a slat system. Clamps lay flat with your material reducing the risk of hitting a clamp and damaging a nozzle. These smaller clamps can be positioned anywhere on the table, and material of any shape or thickness can be clamped into place in seconds. This is yet another advantage of using grates over a slat support system. This simple, easy-to-use, effective clamping system holds the parts to the grate and further increases efficiency and production time.

A study of actual downtime has shown loading and unloading parts, including clamping and setting up is the single largest loss of revenue in the entire business.

When purchasing grates it is important that you look for the following specific characteristics: grates must be flat, rigid and resist waterjet cutting damage. They should be reversible in order to have an “extended life”, have substantial load bearing capacity and incorporate a clamping, jigging and fixturing system. Look for grates that can be made to fit any waterjet table as a retrofit, giving older used waterjets a competitive advantage over newer systems that do not have quick loading and unloading capabilities.

The resulting increase in production can be phenomenal when using a grating system with easy clamping and fixturing as opposed to the traditional slat support system. By switching to grates hours can be shaved off of set-up time increasing efficiency and production. This is something every waterjet user could benefit from, regardless of the age or make of the waterjet being operated.