Low-cost 4x4 plasma table, finished.

[Fiero Addiction]

I just finished building my plasma table and have been running it for about a week, I figured I'd show a few pictures. I spent a lot of time here looking at pictures of other people's builds for ideas, hopefully someone can get something from mine. My initial goal was to spend $1000. It ended up being closer to $1500.

The table is made from 4"x2" 14 ga steel tubing, fully welded. It's 64" long by 60" wide. The material support slats are 1/8" x 2" flat bar on end, 4" apart, supported at each end and in the center. The table has a built-in water tray, 18 ga steel sheet welded to the bottom of the table. The air tank underneath the table is the air bladder to adjust the water level.

For the X axis linear guides I'm using a 72" ground Vee rail and Vee rollers on one side, bolted to 1x1 steel tubing which is welded to the main frame of the table. The opposite side is the same except that it uses flat rollers on a flat rail. The X carriages are cut from 1/4" steel plate. Each carriage has two fixed rollers on top and two smaller rollers in adjustable slots on the bottom. The gantry is made from 2"x2" uprights and 4"x2" cross beam, welded to the carriages. The Y axis uses two V rails, one bolted to the top and one bolted to the bottom of the 4"x2" gantry tube. I have rails on both sides of the gantry, the second set will be for a drilling head.

The X and Y axis are driven by timing belts and steppers. The belts are 3/8" width .2" pitch XL series polyurethane with kevlar strands. The belts are fixed at each end, wrapped over drive pulleys and tensioned using two double skate bearings as idlers on each belt. Both axis are direct drive with 15 groove pulleys on 210 oz/in NEMA 23 stepping motors, two on the X and one on the Y.

More later...

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[Fiero Addiction]

The Z axis is a linear stage assembly that I found on Ebay. I think it's from some kind of silicon wafer handling machine. I got two of them for ~$120 including the motors. I made the plasma torch holder from a block of aluminum, it's mounted on some miniature THK linear rails to activate the tip contact switch.

The control box is 12"x12"x6", should have been larger but it's what I had. It holds a Cosel 24V 15 amp power supply, A Mechatronics 4 axis driver board, a four output isolated relay board, E-stop relay, cut/drill switching relays, 5V power supply with 5 optoisolated input channels, Torch height control board, two fans, and front panel controls and indicators.

I can traverse at 200ipm. The X has trouble going any faster than that with these little motors. The Y will do 300ipm without any problems. I'm driving the motors at twice the rated current and 4 times the rated voltage, they don't even get warm. I'd like to push them harder, but I'm just about at the limit of the drivers. I haven't noticed any missed steps yet and it moves faster than my plasma cutter can cut, so I guess there's no need to change anything.

[Weldtutor]

I just finished building my plasma table and have been running it for about a week...

Nice looking project you have completed.

Thanks for sharing the construction information & finished pictures.

"Happy cutting."

[madmike357]

thats a good lookin table how many gallon is your water tank?

[lamicron]

Do you use any chemical to keep the water clean of rust ? My water table is full of it...

[Fiero Addiction]

The table volume is about 60 gallons, plus about 15 gallons excess in the tank, so the 80 gallon air tank is nearly full when the table is empty. I added about .05% by weight of sodium nitrite (not sodium nitrate!) as a corrosion inhibitor. I'm using n-alkyl dimethyl benzyl ammonium chloride and n-alkyl dimethyl ethylbenzyl ammonium chloride as an algaecide. These chemicals are both widely used for cooling water treament. I also added an ounce of blue dye so I remember not to drink the water!

Here's the recipe for home-made PlasmaQuench
1/4 pound of sodium nitrite powder ($15/pound)
1 teaspoon of Physan 20 ($8/8oz bottle)
1 oz Ultramarine blue food-grade dye ($5/oz.)
Mix well, treats 75 gallons of water.
All prices include tax and/or shipping.

It seems to be working very well, the slag in the bottom of the table is not rusted at all, and it also prevents the sheets and cut-outs from rusting. I haven't been using it for very long, but the water is as clear as the day I put it in. The blue dye is starting to settle out, maybe I should have used liquid dye instead of powder, but it's not important anyway, the color was just for fun.

Edited to post some pictures of the bottom of the water bed.. no rusty muck, just shiny beads and black dust. The slats were rusted before I installed them.

[txcowdog]

Excellent build at an affordable price. You have done a great job. Now I'm jealous.

[DRL]

Fiero,
Thanks for the recipe. You named 2 different ammonium chlorides, are they both in the Physan 20? What about a source for them?
Great looking table. I love your belt drive. I've been thinking of doing that with small roller chain, just like your Y axes, with the chain laying flat, supported, instead of hanging in midair like if it were a loop. Easier to adjust tension.

DRL

[Fiero Addiction]

The Physan 20 is marketed for home and garden applications as a general purpose disinfectant, fungicide, virucide, and algaecide. It contains both of the amonium chlorides. You can get it at a garden center or greenhouse supply, or online retailers such as Amazon.com. The label gives instructions for treating pools, you can scale it down for whatever size your plasma table is.
The Sodium Nitrite should be about .05% by weight. Just calculate the weight of the water in your table, multiply by .0005, and add that much Sodium Nitrite.

Check Ebay seller quartzpegmatite for Sodium Nitrite
Check Ebay seller heavenlyorchids for Physan 20

http://www.physan.com/

I've been using the table just about every day since I finished it. The fun hasn't worn off yet. I'm running out of metal.

[Fiero Addiction]

Well after a few weeks of use and an upgrade to an Esab 875 plasma cutter, one of the allegro 3977 chips on the Mechatronics board let it's smoke out! I just replaced it with Keling 5042 drivers and it was a huge improvement to the machine. I can now get 700 IPM from the X and 1200 IPM from the Y, accelleration at 100 IPS/S with lots more power than it ever had. I had blamed the little 210 oz/in motors for the poor performance when it was really the drivers. The acceleration is still not fantastic, but it's satisfactory.

I'm noticing some minor white corrosion on the galvanized bed of the water table. The steel slag and dropouts are still not showing any rust, and the water is still clear. It gets a nasty muck on the surface after cutting, but after a down/up cycle it's clean again.

Jon

[TT350]

Man that is a first class job!!
I like the belt setup.
Why did you choose belts over
rack and pinion?

[Fiero Addiction]

I used belts for a couple reasons. They are easy to tension and virtually backlash-free, no need for the spring-loaded pinion to keep gears in tight mesh. Belts don't wear (much) and don't require lubrication. If a belt gets damaged, it's cheap and easy to replace. They were about half the price of rack, at least from the suppliers I was dealing with. The 3/8" belts are a little small for the X axis, I can visibly see some belt stretch when accelerating or decelerating at high rates. I would go 1/2" or 3/4" if I did it again.

I was a little concerned about direct driving the belts when I was building the machine, most of the info you read on this forum will tell you that you need further reduction, but for plasma cutting you really don't. My resolution is more than good enough for plasma cutting, and it has plenty of torque to move the heavy gantry and torch around. I can put a pen in the torch holder and draw shapes on paper with no visible steps.

[TT350]

Thanks for the info.

[TT350]

Where did you get your THC?

[Fiero Addiction]

I made my own THC based on the schematics in the older Mach user manual. It has been working very well.

[TT350]

Is there a link to the info?

[Mongkol]

Hi Fiero,
Do you use the plasma cutter with manual torch to link with your plasma table? What brand and model do you use?

Mongkol

[Fiero Addiction]

TT350, The schematic for the THC can be found in the Mach2 user manual, section 12.2.
http://machsupport.com/docs/Mach2Mill_6.11.pdf
I made some changes to mine, but if built the way it's shown, it should work just like the THC-300. It provides torch-up, torch-down, and arc-good outputs. I'm using Mach3 and it integrates very well with the built in controls. Figure 12.2 is the voltage divider and filtering circuit that mounts in or on your plasma source. Figure 12.3 is the circuit that compares the scaled arc voltage to the set voltage and generates the appropriate up/down output signal. It also has fault detection and voltage display circuitry.

Mongkol, I started out with a Thermal Dynamics 35C and hand torch (seen in pictures) but I now use an Esab PCM-875 with a hand torch. The Esab has connections for the torch-on and arc-good signals, as well as a 20:1 scaled arc voltage.

[lamicron]

How are your belts working? Is there any backslash? I´m building a new plasma table and really want to work with belts! You tell about using the 1/2 " in belt ( H ?) Is it ok? i was thinking to use a t5 o t10 ( 5mm or 10mm) which one you thimk will be better<?
Thanks
Luis

[510rob]

Fiero,

I looked up the specs on your ESAB PCM-875, and specs are 10-60 amps output range. What is the maximum thickness of steel that you have cut with that plasma machine? What kind of thickness could you get from your original plasma machine?

Oh yeah, your machine looks very well constructed too - nice job!