It’s important to support the glass work piece from the bottom with something that provides even support, yet is soft enough so the jet doesn’t ricochet back into the glass and frost the bottom surface. Waterjet brick is a great option for this. Make sure the support surface is flat and uniform to avoid cracking the glass. Be sure that the glass work piece and the support are secured in place. Clamps, weights, and tape can be used to secure the work piece, depending on what the cutting situation calls for. Failure to ensure the piece is secured in place results in artifacts such as jagged edges on the cut or other cutting inaccuracies.
2. Use Fine Mesh Abrasive
A good quality abrasive always provides better waterjet parts, but it’s particularly useful when working with difficult materials such as glass. You may find that higher mesh sizes (100, 120, or 150) at a flow rate of about 0.4 lbs (0.2 kg) per minute give smoother results with less microchipping on the edges.
When cutting mirrors, use a finer abrasive to avoid chipping of the reflective paint. Similarly, cut with the reflective paint side down (so you can see yourself in the mirror), on top of a waterjet brick or other sacrificial material.
4. Eliminate Sagging in Abrasive Line
Make sure there is no sagging in the abrasive line. Sagging will interfere with the flow of the abrasive to the nozzle, and can cause cracking when piercing. If necessary, shorten the abrasive line to eliminate sagging.
5. Ramp Pump Pressure Slowly
Slowly ramp the pressure from the pump beginning at zero, so that only the lowest pressure water hits initially while the abrasive is beginning to flow.
6. Pierce Using Vacuum Assist
Use the vacuum assist accessory to pull the abrasive through the nozzle, so that as soon as it starts, the abrasive is already flowing. The abrasive should be on before the water has a chance to reach full pressure.
7. Pierce at Low Pressure
To avoid cracking the glass, use the lowest pressure that your pump can produce while still having enough vacuum to pull the abrasive into the nozzle without the nozzle plugging (typically 10,000 to 15,000 psi [69000 to 100,000 kPa]).
8. Make All Pierces Before Cutting
Perform all the pierces first before doing any cutting. If done this way, the pressure in the plumbing stays consistent and reduces the risk of shattering the glass. After piercings have been done, the glass can be cut using high pressure. In designing a path, take care to ensure the cutting operation starts inside of any holes that have already been pierced.
9. Use Brittle Cutting Mode
If using OMAX software, be sure Make sure "Very Brittle Material" is checked when working with glass.
10. Plug MaxJet 5 Nozzle Vent Hole
When using the MaxJet 5 nozzle, plug the vent hole to create additional vacuum pressure at low pump pressures. This will reduce the life of the jewel slightly, so you should only plug the hole when necessary.
11. Avoid Big Temperature Changes
Watch out for dramatic temperature changes between a hot water tank and cold air or water which can cause your glass to shatter. For example, if you pull your freshly cut glass out of a hot water catch tank, avoid hosing it down with cold tap water.
12. Use Long Lead-ins
If you have the room, use long lead-ins so that if a crack does appear at the pierce point, it is less likely to make its way all the way to the edge of your part. When "Very Brittle Mode" is checked, the length of lead-ins is not automatically adjusted for a dynamic pierce, so the length in your drawing is the length that is used.
Do not attempt to machine tempered glass, as it will shatter.