Looking for tips on building hybrid water table / downdraft setup

[calsdad]

After looking for years - I finally pulled the trigger and bought a CNC plasma table. Found a really good deal on a Dynatorch XLR8 4x4 setup that came with a Hypertherm Powermax 65. I just have to finalize the deal - and get the thing back to my shop to get it setup and running.

Since this will be running in a crowded shop and I'd like to keep the fumes to an absolute minimum, so I'm contemplating a hybrid water table / downdraft configuration like I've seen on Jim Colt's trade show demo table and like Keith Fenner has on his Plasmacam system on Youtube.

What I'm looking for - any suggestions or tips on how to go about doing this. If I go with a water table - should use a "bladder" setup - and how is that constructed? , what do you use for a tank? How do you design a decent downdraft system? .... etc. These are the kinds of questions I have.

I've got a relatively well outfitted shop already - with a 4ft metal brake, welder , press - etc. So I think any setup I come up with I should be able to fabricate myself. I'm going to have to - to keep the costs down. The wife's already a little peeved I spent the money on the table

[Scratch]

Id like to see a details of Jims downdraft water table...
Paging Jim Colt...
Jim Colt to this thread please...

[jimcolt]

Here are some pics of the two 2 x 2 cnc machines with Hybrid downdraft water tables being built for use at trade shows.

- The water needs to be 6 or more inches below the material to eliminate splash that affects cut quality.
- The downdraft needs about 3200 cfm and high static pressure to pull the remaining fumes for a 4 x 4 table design, pull the air down around a central water tray which you can see in these pics.
-This unit used Torit brand welding fume filters, which I would not recommend for production use (perfect for trade shows. Either use a cleanable welding fume filter or blow the downdraft exhaust outside.
- I could not find fans with adequate static pressure (vacuum) so I bought parts (fan blade, TEFC motor, guard) and then fabricated a shroud to make the fan more efficient.
-I'll answer any questions. Jim Colt Hypertherm

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[East German]

Hello,

Here is my version.
Peter

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[calsdad]

Thanks Jim and Peter for the pics - that's very helpful.

One of the design considerations I was wondering about was how much ducting do I have to do to get the air to flow equally around the perimeter of the table. From looking at your setups and watching the Keith Fenner Plasmacam setup on Youtube - it seems like having some sort of "covers" around the perimeter of the table is really the important piece of the puzzle- to get any fumes remaining that the water table does not catch - to flow into the downdraft.

I won't know for sure until I actually get the Dynatorch table back to my shop and take a look at it, but I've been checking out every online pic of a XLS or XLR table I can find - and it looks like the table on those models should be adapted relatively easily to a water table-with-downdraft setup.

I had previously been looking hard at the Dynatorch SuperB tables - but the configuration on those looked like it would have been a lot harder to adapt to a dual setup.

[East German]

The exhaust air duct.

Peter

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[calsdad]

Nice disguise on your exhaust duct Peter.

Looking thru the pictures that you and Jim Colt posted - I see that both of you seem to only be pulling air for the downdraft from two sides. On the 2x2 table that Jim Colt has - I can see how this would work fine. How well does that work on your table Peter? Judging by the pictures you posted I'm guessing that your table is approximately 4 foot by 6 foot (120 centimeters x 180 centimeters) ??

I have been operating under the assumption that I would need to be pulling air from all four sides of the table ( the Dynatorch I am getting has a 4ft x 4ft table) - and that to get equal draw on all four sides - I might have to do some sort of ducting setup under the table so the fan pulled equally from all four sides - or maybe I would need a separate fan for each side of the table (might be easier actually).

I can't really find any detailed information on how to build a good downdraft table setup on the web. I see lots of CNC plasma table companies advertising their table's downdraft setups as being "efficient" and "not needing to be zoned" and so forth - but I can't find any details on how this is done.

If I only really need to draw air from two sides of a 4ft x 4ft table - that would simplify things a bit.

The setup that Keith Fenner has on his Plasmacam - only pulls from two sides, although technically I think it's probably better classified as a side-draft rather than a down-draft:

https://www.youtube.com/watch?v=azMBySf ... lOZa4JtX8C

[calsdad]

Here's a question about water height:

Jim Colt said:
" - The water needs to be 6 or more inches below the material to eliminate splash that affects cut quality. "

I believe this was in regards to cutting steel (not stainless).

In my travels I've read a number of people who said that they found stainless cut best when fully submerged. Is this something I should take into account? I don't have plans to cut a lot of stainless - but if it's a requirement to cut submerged - or a really good idea .... I'd like to take that into
account when planning how to setup the water table.

[motoguy]

I've only cut 1/8" stainless, but I cut it above (not submerged in) water. It cut as easy/well as regular mild steel. The only issue I have with stainless is the blackened edges, and cleaning them up. As that's an oxygen issue, I don't think cutting under water would cure that, but I could be wrong.

[calsdad]

I've been looking around to try and find some consensus opinion - and there doesn't seem to be one on whether water below vs water touching and/or submerged is the best

This article
http://multicam.ca/open-air-vs-underwat ... a-cutting/

points out that Hypertherm True Hole (which my Powermax 65 does not have) or Fine Cut (which I probably will use) function best when not submerged. It also said that Ohmic sensing (not sure if the Dynatorch has it - whether I need it, etc) does not want to be submerged.

I suppose that the best of all worlds is to make the water level variable in the water table - but there's a pretty big variable between having 4 inches of water in the table - and having that water 6 inches below the cut piece .... and having the piece submerged. It's going to make for a somewhat complicated setup. Plus an awful lot of water to store if I go for some type of bladder system

[tcaudle]

With water too close it blows up and gets into the torch. If you have ohmic sensing it causes false touch offs. If you have any electronic form of Collision Detection, same thing. The settings for cutting can be different if the water is too close. While it works to rapidly dissipate the heat and causes a much smaller heat affected zone at the cuts it siphons away some of the cut energy. Over the years I have gradually moved form water tray to mixed (water and downdraft) and to full down draft. Its not easy to get equal air flow (negative air pressure) over the entire cut area but I have seen it done and its pretty astounding. NO smoke and NO filters. No plume of dust outside. Wish I could tell you the method that works but all I know is its a series of tubes with holes that run under the cut grid and tie to two 12" ducts with two 12" fans (one on each side)

[East German]

My first machine had the water directly on the plate. The splashing water messes up the machine and the sheet. If you cut on the edge it was particularly bad. I did not think that was good.
I like my system very well but the table must always be fully occupied for it to work.

In the company where I work is a plasma system with a work table of 25 x 6 meters.
The extraction takes place via covered tubes. The tubes in the working area of the burner are activated by switches on the table the others are off.
It is always sucked only where the burner is located. This works very well.
The system cuts sheets from 5 to 35 mm. I can not take a picture of it.

I hope I explained it well.
Peter

[jimcolt]

The real key to the downdraft working is not with the cfm rating (cubic feet per minute) rating of the fan being used, rather it is with the ability of the fan to draw an adequate vacuum (AKA "static pressure") under all conditions. Most fans that can do this (tube-axial style fans) are a bit more pricy. It is also critical to have fans with TEFC (totally enclosed fan cooled) motors....or motors that are belt driven from outside of the hot, dirty air produced by cutting.

The nice thing about a hybrid water / downdraft is that the water captures, cools and sinks roughly 60% of the particles (larger particles that are heavier), leaving much less flow requirement for the downdraft. This is the reason I chose the hybrid design for the machines I built for trade shows as there was no means for ducting outside and I had to use filters.....the filters lasted much longer with only 40% dust after the water trapped the larger amount. This same reasoning would work in a heated shop with a hybrid table....much less of the heat would be blown outside.

On the comment regarding nitrogen cutting submerged: If you use nitrogen as the plasma gas in a Hypertherm powermax unit and submerge the stainless an inch or so....you will get a bright nickel colored edge. This is because the water shields the cut face (no ambient air with 20% oxygen content) and pure nitrogen coming from the plasma process.....this keeps the oxidation off the edge. The drawback is that it is hard to find the exact dross free cut speed using nitrogen submerged, so don't expect dross free cut edges. Jim Colt Hypertherm

[calsdad]

If I could just dump the air outside that would be easiest solution - but I'm in a suburban neighborhood and I'd like to avoid (as much as possible) dumping smoke outside the building. So - if I implement a downdraft - I'm just thinking I need to design around the fact that any exhaust needs to stay as clean as possible (and also as non smelly as possible)

Since the fumes also would contain atomized steel - I'd like to either capture as much of it as possible (the reason why I'm thinking hybrid water table and downdraft - the water table would hopefully collect the majority of the steel dust) - or filter it out if possible.

If I could keep the air inside the shop by filtering it - that would be great. No external exhaust would just make things simpler.

I have a Lincoln Mobiflex 400 welding fume extractor - and I've read a lot of literature around the *welding* fume extractors , and it seems they universally recommend to NOT use them to extract plasma cutting fumes. I'm assuming that's probably because the plasma process is creating atomized steel - which is different from a welding process where it's really just fumes.

I found this Tempest Air weld fume extractor - which seems to use relatively commonly available filters - in stages: first a spark arrestor type filter, then a commonly available HVAC filter - and lastly a MERV-16 filter (the most expensive but also the longest lasting).

https://tempest-air.com/?gclid=Cj0KCQjw ... RhEALw_wcB

I'm wondering if some sort of staged filter setup would work on a plasma table - especially if a water table was present gathering the majority of the fumes and output from the plasma torch...............