I am keen to do the same thing, anyone have any info on what has been done before ?
Seeing some of the rolling beds makes it seem possible to have both downdraft and water separately with one sitting over the other and just roll out which ever one you don't use. I think theres probably a better solution in a combo bed where you can drain the water and turn on the fan. I'm thinking of evenly spaced ducts coming in the bottom of the table. You could just flood the ducts to keep it simple but valves would be good for having a Zoned table anyways.
Maybe we should have the argument first of why would anyone want downdraft instead of water:
Water seems great but its not for everything. There does seem to be two types of water table users users(the work piece is completely submerged or touching it users and the water is just below or way below my work piece users) While there is no doubt that touching or a hair below is best it brings up the point that water still works pretty good as long as you can just get the dust particles to touch the water before they get out into open shop air. Same principle as an oil bath air filter on an engine. A *nonflamable* oiltable would probably actually be pretty good. Anyways, the point is, maybe air circulation should be engineered(fans) to circulate the air down toward the water for times when the workpiece can't or shouldn't touch the water. Nonetheless I think a downdraft table would sometimes just be better. Here are the scenarios:
Tall work pieces: If i want to cut holes in the top of an ibeam or side of a box tube that is deeper then my water table. This is where i think removable slats would be good, but that just means you can cut even bigger pieces that will still stick above the top of the watertable.
Pipe Cutter: I was thinking of building a partially submerged rotating axis, but downdraft would probably be smarter.
Most people run those topside bristled vacuum dust collectors(see pic). But that is only good for 3axis work and you can't see what the heck is going on under there.
Aluminum and Hydef gases:
Alot of people say a water table is dangerous for aluminum. As a childhood pyro I'm very skeptical of being able to build up enough explosive gases of any kind under a flat work piece with water barely or almost touching it to cause any body or machine damage-theres just not enough volume if your water level is correct. When i'm bored in the shop I blow things up with my oxyfuel torch and it doesn't take much, a bottle cap is deafening, a spray paint cap will take off a finger and a 2 liter bottle could take off an arm but thats with an optimum & concentrated mixture. My only concern would be moving the sheet or distorting it during cutting. I'd love to see proof otherwise. That being said, I'm not so sure i'm going to have an enclosed water chamber. "Oh cool, I can fill up my bathtub with my air compressor" just isn't cool enough to me.. I'll probably use an open top with a pump. Is anybody filtering their water?
So what do you think?
I am keen to do the same thing, anyone have any info on what has been done before ?
I have a water table with a curtain around the machine with a mezzinine above it (so the machine is enclosed) with a furnace fan to extract what the water dose'nt
How high off the table is your mez? Does it get in the way? Post up a pick.
Still looking for good ideas. I like the curtain idea, but my sheet rack is 10ft tall and sits right next to the table which has a hoist above it so it would have to go all the way to the ceiling, And i think that welding curtain stuff is expensive.
People are scared to build a waterbed because they dont have enough knowledge about electrolyses and HHO gases. I am running HHO cells on my vehicle,so I have a pretty good understanding(Its not just alum. its copper and S.S. also). To make HHO gas it takes a while, what usually happens is the gas gets trapped underneath the cutting material and above the waterlevel, capturing an air pocket with explosive HHO gas. When the plasma cuts into that air pocket, boom...... Now why is the HHO gas getting trapped? Material is warped, water is stagnent, waterlevel right at bottom of material...etc Buy a small submersible waterpump from home depot and submerge into the tank. This will keep the water circulating and pushing the HHO gases to the edges and going into the air. Also, I have an external tank for my waterbed. I can pump water from one to the other w/ no problem to regulate height. When you drop the water level down you are also purging out the HHO gases from being trapped under the material. Wouldn't recommend an air bladder, HHo gases get trapped in these, go w/ an external 100 gal. plastic tank or something.
The waterbed has to many advantages to just say its dangerous im not using it. For one it takes 90 % of the vaporized fumes out of the air. Keeps material from getting to hot and warping. You shouldnt need an exhaust fan if you use the watertable correctly..
I'm designing the water table for my plasma cutter right now...
My plan "A" was to have a very shallow water pan. just deep enough for the slats. There would be no way to have circulation. Is it necessary to be deeper?
I'd think you would want at least 1"-2" of circulation area underneath the slatas for water to move around, & dross to collect before sealing off these areas.
If it works.....Don't fix it!
There are 10's of thousands of water tables in North America with internal steel bladders...that are used with plasma cutting on a daily basis. Properly designed...there is no Hydrogen or "Browns gas" present in the bladder. There occasionally is a small amount of Hydrogen produced by dissociation when cutting aluminum....however it is such a small amount that it normally rises out of the cutting bed and disipates in air.
Water pumps in cutting tables are generally not a good idea....they do not last long! It is normal best practice to use compressed air power to raise and lower the water in cutting tables.
Also.....any depth of water in a pan under a plasma torch (the closer the better) will cool and sink the largest particles produced by the cutting process, however, many of the smaller particles that are hot and lighter than air will rise out of the cutting bed. A combination of downdraft and water works rather well...as the water traps about 60% of the particles....making the job easier to pull the remaider from the cutting area.
Last edited by jimcolt; 04-28-2009 at 07:59 AM.
Yes, I agree 100% with you, I am just trying to give some advice to people that are designing a watertable. There are many watertables with internal bladders, I was actually going to use one on mine. I have seen designs with not air bladders (they will work fine)but steel boxes in the tank. But who is to say the steel bladders dont have HHO gas in them. They probably just havent seen a spark yet. I just feel safer going with an alternate design that has no trapping effect what so ever. One cubic inch of HHO gas will blow your hand off. That amount can be produced in less than three minutes while cutting....But I decided to go with another method. I wanted to have a movable waterbed so I can take it outside and clean it out. That is my purpose of the external tank also, so I can remove the water out of the one transfer it to another, go clean all the debris out, then fill it back up with the same water. When you start adding internal steel bladders and such the weight was to great for two people to carry with debris. As for a pump they will get clogged up with debris if no filter is used.
Question (thinking outside the box) What other liquid can be used in the place of water so HHO gas does not produce? Or is their a chemical that can be added to water...
Once again....the hydrogen (and from everything I've learned in 31 years at this....its hydrogen...not HHO) is formed only when you cut aluminum......the byproduct of cutting aluminum is aluminum oxide...which sinks in the water and then absorbs oxygen from the water.....since water is comprised of oxygen and hydrogen, and you take some oxygen away....you will leave hydrogen. The hydrogen bubbles normally rise to the surface and disipate in the room air. If you cut steel or other materials only...then this is not a problem. It is recomended that if you cut a lot of aluminum over a water bed...then you should install some pipes with holes drilled in them in the bottom of the table....with compressed air plumbed to them...this tends to dilute any small amounts of hydrogen. I suppose a small amount of aluminum oxide could somehow find its way into the air bladder of the machine......I've just never heard of an issue with it. There have been a few explosions when hydrogen is allowed to build under a large plate on a table (over the weekend?) and the operator fires the torch on monday morning to a surprise. With the air bubblers this likely would not happen...or just by raising and lowering the water once it probably would not happen. You can actually dump bicarbonate of soda in the water and the hydrogen production process will stop...although I would suggest talking to a chemist before making that recommendation.
We are not getting anywhere with this conversation and I dont want to argue. The objective of this forum is to give people Ideas on waterbeds and downdrafts. Here is a article I copied off a scientific website. HHO gas is formed by a small DC current ( which comes from the plasma negative ground cable and when it cuts) not when alum. oxide falls to the bottom of a tank. And yes it can happen with S.S. and copper ALSO. I am running HHO cells on my vehicle and have used all 3. But Alum. makes the most by 30 %.
HHO gas is "cracked" H2O.
It can be produced through electrolysis by running a current through a positive and a negative electrode submerged in the H2O.
IT IS VERY FLAMMABLE AND CAN EASILY EXPLODE!
HHO is not water vapor (H20 in gaseous form). It is Hydrogen and Oxygen gas that has not bonded into H20.
Currently there are numerous uses and experiments being conducted to run Automobiles on HHO with some very successful results.
This whole process can be very beneficial for you when used in an engine. By extracting the HHO gas from the container in which you perform the electrolysis and into the engine through the air intake you can drastically increase fuel economy and get better gas mileage as a result. With the price of fuel being so high and with prices set to rise further there is no better time to reduce your fuel consumption! It works by increasing the octane rating of the fuel so you combust more of the fuel as opposed to wasting it out the exhaust.