Water table vs. Downdraft is about like a Ford vs. Chevy debate with some people. I’m going to try and stay as neutral as possible despite having a clear preference. Let me first say that unlike many people who will chime in on this I have had a table that was open - no down draft no water, A downdraft table and a water table. For the Westcott ProSeries table that I just purchased I went with a water table so after having all three before I went with the water table again.
I’m not going to spend too much time talking about an open table, by that I mean there is no water table and there is no down draft system. There are just slats for the material to sit on and nothing but ground below. This style is extremely messy and will fill your shop with a fine black dust that will coat every surface in short order. Its obviously the least expensive option but also the worst for many reasons. Avoid this option at all costs.
Lets look at some advantages and disadvantages of a downdraft system vs a water table system:
The tables above represent a few of the pluses and minus on each side. Lets break it down a bit further. With a downdraft system you are using a table design that tapers down under the table to an exhaust duct. This duct is then connected to a fan to pull the air, dust and smoke down and away from the table. If the table is not designed correctly small parts and pieces that drop down can be difficult to retrieve. Table position in the shop is critical since you will need to place it close to an exterior wall or use a vertical stack for ventilation. The ducting can be a trip hazard and obstacle around the table. Your going to need a large and powerful fan to pull all of that smoke and dust down. Picture a 4x8 table, you have 32 square feet of space you need to pull the air down evenly across this entire space and exceed the tendency of the smoke to rise from heat.
The design of the downdraft system is critical so that it effectively pulls the smoke and dust down over the entire area and not just the center. This is an area where I often see downdraft tables fail. They may pull the smoke and dust down when cutting over the center of the table but when cutting anywhere else its not effective. Also you need to usually cover areas not in use to increase the vacuum affect. If you have a 4x8 table and your cutting a 4x4 piece of steel. The down draft system and the air will take the path of least resistance and be pulled through the area where there is no steel and allow the dust and smoke to escape where your cutting.
All of the air that your pulling through this system has to come from somewhere right? That air is your heated shop air in the winter and your cooled shop air in the summer. So your going to be pulling hundreds of cubic feet a minute of air out of the shop. This can dramatically increase your utility bills. Venting direct to the outside is common but it can make a mess of the area where it vents and you will have the smell of smoke being pushed outside. Units to clean the air and reuse it can cost thousands of dollars. And you will have more noise and electricity use due to the operation of the fan.
Lastly with a downdraft system your metal will be hotter and stay hotter longer. Warping of thin material is much more common and will give your THC a work out keeping up with the warping material. This warped material can also be a pain to deal with when finishing the part. You can often just look at plasma cut parts and determine visually if they were cut on a water table or a downdraft. There will be a blue haze around the downdraft cut parts edges from the extra heat the metal experiences.
With a water table your using a contained bed of water to capture the heat, smoke and dust. Most water tables are 4 to 6 inches deep across the entire cutting area. Some have sumps where the water can be drained off when not in use to allow for retrieval of small parts, table cleaning and to decrease evaporation rates. You can vary the water level in the table with a hose for low end tables or using air pressure in high end air bladder tables. Water level is critical to the effectiveness of the table. I have found that ¼ to 3/8 below the bottom of the material being cut works best. For certain applications like cutting Armor plate I will raise the water level and cut the plate underwater. You can see a video about that here: Cutting AR Plate Video
Because you have the water as a cooling media the material your cutting stays cooler so you have less warping and less Heat affected zone HAZ and discoloring around the edge of the cuts. Maintaining proper cut height is critical for getting the best quality cut, if your material stays flat and does not warp its easier for your machine to maintain the proper cut height across the sheet.
A water table will help reduce the amount of noise from cutting as well, except when it cuts around open areas or edges where there is a lot of air and splashing noise. But you do not have the added noise of a fan or that added energy consumption that you would have with a downdraft system.
With a water table it will be a bit messier and a bit wetter than a downdraft system. I like having a hose or a garden sprayer to wash off the parts when they are finished cutting. I also keep a small work table next to the cutting table with a towel so that I can dry and wipe off the parts after cutting. This is a step that you would not have with a downdraft, but parts are cooler and can be handled much quicker with a water table.
The water in your water table needs to be maintained and monitored to be effective. Check our or page on water treatment here: Water Treatment Page
As with anything there are advantages and disadvantages to both. Is there a clear winner? For me there is, hands down I prefer a water table. I have used all three types and just purchased my second water table. Review all the information and consider your application and your site and make a decision for yourself. Have questions? Want more info feel free to email me.