Many metal fabricators determine the shop layout and setup of their CNC table prior to buying the cutting system. Therefore, a lot of thought goes into whether a fabrication shop will be using their CNC plasma cutting system as a down draft or water table.
What’s the Difference?
A down draft table uses an exhaust fan to suck the metal smoke through the plenum in the bottom of the table bed. The smoke is filtered and sent through duct-work from the table to outside of the building. The pictures below show the exhaust fan, duct-work, and down draft plenum.
Water tables use a sealed frame to hold water inside the bed of the table. Typically the water level is just below the bottom side of the material surface allowing the water to capture the smoke when cutting. Another benefit of cutting over water is that the parts will cool down quickly making them easier to handle.
If you’re using the plasma system as a water table, it’s necessary to pour an anti-corrosion additive in with the water to keep the table bed and slats from rusting. And, be very careful with these anti-corrosive products as they contain hazardous chemicals.
Deciding often comes down to these three things: shop location and layout, the material being cut, and the required cut quality.
Shop Location & Table Layout:
Many times the physical location of the building will determine the down draft versus water table decision. For example, these common issues often lead a business owner to choosing the water table option.
- Heavily wooded areas, residential neighborhoods, and certain business parks are not ideal or will not allow for smoke to be send out of the building.
- The CNC plasma table is not close enough to an outside wall or exhaust system necessary for the down draft setup.
Mild steel and stainless steel usually do not have any issues being cut over water. However, aluminum is a different story. Cutting aluminum over water can cause hydrogen bubbles that create loud (and frightening) explosions. Sometimes lowering the water level can help reduce the likelihood of this happening. However, if you are cutting mostly aluminum then a down draft setup is probably a better option.
Many plasma experts, such as Jim Colt at Hypertherm, have found that they get better cut quality when using a down draft setup. Cutting over water can sometimes cause roughness on the material’s edge or unwanted dross on the bottom of the plate. Watch the video below to learn what Jim Colt thinks about the down draft versus water table question.
All EZ Cut CNC Plasma Cutting Systems can be configured as down drafts or water tables. We offer 4’ x 8’, 5’ x 10’ and 6’ x 10’ turn-key CNC plasma cutting systems. On-site installation and training is included with all EZ Cut CNC plasma cutting tables.
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