water or downdraft

[brewman114]

I would just like to get some input before I start to modify. I own a 4x8 plasmaroute table and am thinking of modifying it to be a water table. You see, right now it is just open at the bottom and plasma dust goes everywhere. The benefit is that the small parts that fall down are easy to get to. So my question is what are the opinions of folks here on which is better Downdraft or water. I think the downdraft would suck too much heat out of the shop in the winter but I could still get to my parts easier. The cost of modifying would be more than a water bed but I could get to the small parts easier than searching in the water. Water would be cheaper but not sure how well it controls the dust. I do not cut much aluminum either so Hydrogen shouldn't be an issue. If I cut any I would just open the doors to the shop for ventilation and suffer with the cold air like I do now.

Thoughts or opinions anyone?????

[JJsCustomDesigns]

I vote Water Table. I built a downdraft when i first got mine. It seemed like a good idea cause it was cheap. Its a whole different table now that i put a water tray in it. I can actually work in the shop while the machine is cutting.

[brandon350]

I have had both, I vote water table I will never go back to down draft, parts fall down and get lost, dust everywhere, and the cost of a dust collector in a production enviroment

[jimcolt]

I wrote this a few days ago....and since it seems to fit the posters questions regarding water table or downdraft...I am pasting it here:


The two choices for fume control....which is necessary for cnc plasma cutting....are with some sort of a water table/water tray....or a downdraft table. Each method has its pros and cons...here are a few:

Water table,

-On a small machine (under about 5' x 10' cutting area) a water table fume control can often consist of a simple tray or pan....about 4 to 10 inches deep that holde water...the level of water can be either at the bottom of the plate...or up to a few inches below the plate to trap fumes. This is the cheapest, easiest way to trap particulates from the cutting process.

-More complex water table designs have deeper tanks with removeable slat assemblies, as well as pnuematicalled controlled raise/lower mechanisms to control water level...necessary in order to get all of the benefits to cut quality in a water table. These tables can get rather costly...especially on larger systems.

-disadvantages of water tables? Rust on the slats, rust and stains on the plate being cut. Water can splash on cutting machine components. In a small shop that is not heated at night...freeze prevention (chemicals or heaters) must be used. Water splasing on the cut edge of steel will cause additional edge roughness and more probability of dross. Speeds often have to be a bit slower than with dry cutting. If the water table is not cleaned often (weekly)...the slag can often be difficult to clean out.

-Advantages of water table? Very good fume control. Some noise attenuation, and when cutting submerged UV attenuation. There are some stainless processes that work better (better edge metalurgy) when submerged. Small parts can be easily retrieved if the table design can quickly lower the water. On thin plate and or long thin parts...less warpage and camber can result due to the quenching effect of water.

Downdraft.

-The simplest downdraft is simply using a closed in area under the cutting table slats as a plenum, and using some sort of fan to draw the fumes from the plenum....then ducting the fumes outside...or to a filtering device. On an entry level 4 x4 cutting machine....about 3200 to 3600 cfm of air flow is required to effectively remove fumes from a 100 amp or smaller plasma. The lowest cost version.

-More complex systems....as used on larger industrial tables often use zoned systems with a series of mechanical dampers so that fumes are only drawn from the area of the cut. There also are downdraft tables with relatively complex self cleaning features (chain driven blades in the bottom that are used to drag the slag and droppings out to one end of the table for easy cleaning/removal).

Advantages over a water table:

- Generally better cut quality on steel.....smoother edges and less chance of dross. No water splash, staining or rusting issues on the plate or the machine. No freezing issues. relatively simple and low cost....if the fumes can simly be blown outside. Easy to clean out the slag...usually shovels out easily.

Disadvantages:

- Larger tables that required zoned systems and or fume filters can be very expensive. Systems that blow the fumes outside are also blowing the heat from the shop outside.


Hope this helps a bit!

Jim Colt Hypertherm

[Copp3r]

For what it's worth, here's my two bits worth.

Not long after getting my first table a number of years back I made up a tray to fit under my cutting table and went to water. As has been mentioned, at first I loved it. The dust was all but gone. But then I ended up having to retrieve my parts from the water tray and was constantly drenching my hands and arms in at times very cold water.
One of the advantages in the way I set up my table was to have the water just skim over the surface of the steel sheet. The air from the plasma torch was strong enough to displace the water and my cuts were fine.

Then the rust effect came in to play; rust on my sheets of steel, my table, etc. A real pain in the ...

Frankly, filling the water... mess on the floor, etc. I'll never go back to water.

I have purchased a fan from this website (the turbo fan) and I love it ! While only running a 4x4 table ... for now... I have a tray underneath the cutting surface with the fan sucking out the gas / fumes / dust from there. I've got very little off the top of the cutting surface.

About the only thing I'd change is the design of the tray under the cutting table. I'd have it angled to a "V" on one end where all of the small bits and pieces would slide down to; the junk and the parts I need.

That turbo fan works awesome... I relish in watching the fumes and smoke vent out of my shop...

Anyway, as I said... my two bits worth.

Copp3r / roger

[brewman114]

Ok, I have decided to go with the waterbed. I am curious though what are people using as a corrosion inhibitor for the water so the parts that fall through dont just rust up right away. And so the slag that ends up in there doesnt just turn into a big glob of rust on the bottom between cleanouts.

[JJsCustomDesigns]

http://plasmaspider.com/viewtopic.php?f ... ves#p28119

^^ Heres a thread about Plasma Quench. ^^

I use Sodium Nitrite (not NitrAte), which is a rust inhibitor. And Physan 20, which is an algae inhibitor. Both items i bought off ebay for $35 or so for both. Ive had this in my table for 2 months and havent seen the flash rust on the material like i did with just plan water.

Hope this helps.

[Oldsarge]

Another vote for water. When I built my table I adopted a design I saw on Plain 'Ol Bill's table and built it with a bladder style tank. I can raise and lower the height of the water from empty to the top of the slats in just about a minute. It empties even faster. I use a rust prevention product from Miller welding that is made specifically for Plasma tables. It's a little harsh, and but it's safe and effective. I love being able to dial in the water height to the exact place I want. Oh yeah, the I also made my table slats in a carrier setup so that when I want to clean out the table, I can roll the gantry (when I get it) over the table, and hook up to the slat assembly, and and lift the whole thing out of the table. Then it's just a matter of hosing it off, and scooping out the bed of the table, doing any maintenance needed and dropping the slat assembly back in the pan! As soon as I get the gantry and magnet lift hooked up I'll post a video of the process.

Oldsarge

[kbenz]

I'll stick with my downdraft. Much cleaner if done right. we have water tables at work, nasty and messy

[abmetal]

My two cents....I installed a downdraft on our 4x4 table with the exhaust venting outside. Worked great. When we upgraded to a 5x10 table, I stayed with the downdraft system using the same exhaust fan. The only thing I do differently is when I'm cutting small areas I cover the remainder of the slats with sheet metal, cardboard, whatever and I never have any smoke/fumes. Clean up is simple. About once a month I clean out from under the table.
As for retrieving the few parts that fall through, I have a small magnet on the end of a rod that I stick between the slats and just lift them out.
For me, it's simple and cheap...and it looks good.

Allen

[skiwithnoskis]

Anyone have any plans for a water tray for a p-cam 4x4

Thanks
BB

[jimcolt]

Keep in mind if you have the DHC2 or Samson that use Ohmic contact for finding the surface of the plate.....when used with a water table his sensing process is unreliable.

jim Colt Hypertherm

Anyone have any plans for a water tray for a p-cam 4x4
Thanks
BB

[Stout]

Oh yeah, the I also made my table slats in a carrier setup so that when I want to clean out the table, I can roll the gantry (when I get it) over the table, and hook up to the slat assembly, and and lift the whole thing out of the table. Then it's just a matter of hosing it off, and scooping out the bed of the table, doing any maintenance needed and dropping the slat assembly back in the pan! As soon as I get the gantry and magnet lift hooked up I'll post a video of the process.

Oldsarge

My water table has the removable trays with the slats too. It seems to be a really good idea and I may use it some day to get the dust that drifted around the trays and settled in the water table itself. I clean out the table about every two months and pull out about 10 five gallon buckets, at least 200 lbs each, of steel dust and drops for recycling. I just drain the water and shovel out the goo. It always reminds of my first Esab table with no water or downdraft and how much of that steel dust was just floating around the shop covering everything.

For those of you with a bladder for lowering and raising the water level, is it an actual rubber type bladder or a sealed void beneath the water table. Does it require cleaning of any kind? I would think that the floating particulate in the water would wind up in the bladder area where it would settle and then you could not get it out.

The only downside to the water table is having to dig around in the water to find the parts that dropped to the bottom of the table. My hands always look dirty. I'm sure that having the ability to lower the water level at any time is a great option.

[plain ol Bill]

My table has a sealed void type holding tank. I have never had to clean anything out of the tank itself. I do have some old speaker magnets sitting just above the in/outlets to the tank and they have some very light debris hanging onto them. My table has (if I remember right) has about 1-1/2 drop to the drain end. No metal seems to make it to the drain end really, it just drops straight down when cutting and stays there. Most of my cutting is on the one end of the table away from the drain.

[jsw621]

Roger- Could you post a picture of your turbo fan set up. I am interested. My shop is a mess!
Thanks, JSW

[mobiledab]

Air handling is nice and in most cases more effective than water; however, it probably makes more sense for mass production settings with the power (three-phase electric which I don't have) and space considerations. Our vote is for water. Certainly cheaper (factor of 10 less costly in my case) than the high-efficiency downdraft systems and after the investment in the overall CNC, cost was (and probably always will be) a LIMFAC. Did not want to spend the money on a table with an integrated water pan so designed and added our own.

Table is a Torchmate 3 with 5' x 10' cutting area. This was a bolt together table constructed of extruded aluminum and chosen for ease of expansion as well as relocation. We added a separate 3" x 3" aluminum extrusion sub-structure to support a removable steel water tray. In addition to the two end beams supplied by Torchmate, we added three cross beams; all the beams have their own legs as well as HD adjustable leveling feet to match Torchmate's design. The pan itself is constructed of 1" x 1" angle 3/16" thick, 3" x 3" flat 3/16" thick and bent 4' x 8' 16-gauge sheet. Inside is sealed with rubberized spray similar to bed liner matetial, but more flexible. As many others have mentioned, there is an internal slat mounting structure that is easily removed for periodic cleaning and/or maintenance. We also use low concentrations of chemicals to discourage algae and inhibit rust on cut parts. Most everything is cabinet blasted post-cut anyway. We are on the eastern plains of Colorado and the building is not heated. Walls have 6-plus inches of sprayed foam insulation and temp does not drop below 44 degrees F. Water is cold but does not freeze.

[rtsplace]

I did the water table 5' X 8' using 2 30gal. storage tanks and low air pressure to push the water up,2 each 4'X 5' SS trays to help with rust control on the trays. For rust inhibitor I used machine coolant that can be used for plasma cutting as well, little spending if I remember it was about $375.00 for 5 gal. it's concentrated so it goes pretty far Green Cut or something similar I will check, I used it my mill as well. Here's a link to CNC zone build site I posted
http://www.cnczone.com/forums/general_w ... build.html
Ray

[Marty]

not entering the downdraft vs water debate (tho I do have an opinion:):) )

BUT I do have some experience with RUST INHIBITION
The old link is pasted at the bottom

Marty

Here is a detailed post I did awhile back on this subject.....I would not use sodium nitrite personally....I have had exlnt results using Sodium Carbonate (NOT Sodium Bi Carbonate)...the post has all the info you would ever want to know on what works for me anyway ...there are pictures as well...

here is the link viewtopic.php?f=45&t=572&hilit=+water#p28119