[rjengineer]

I've picked up a few tips from this forum, so I’d like to pay it back by sharing some ideas from one of my recent machine builds.

I wanted a 4’ x 8’ CNC plasma table, but I didn't have enough shop space to accommodate one. (Can anybody relate?)

There are a few “portable” CNC plasma rigs on the market, but every system that I examined was either too small or required too much setup time because you had to reassemble and adjust them with each move. I wanted a system that I could deploy and store quickly.

My solution was to fabricate a heavy-duty table that folds up kind of like a Murphy bed when not in use. Here’s the result:
Attachment 254902

The machine weighs about 500 lbs, but can be moved by one man, as long as you’re on smooth pavement. Everything (table, controller, and plasma cutter) is contained in one rolling unit, which makes it quick and easy for me to move the whole cutting operation outside if I want.

In the folded position, the unit is even compact enough (35” wide x 76” tall) to pass through a standard 3’ doorway:
Attachment 254904

It was important to me that the system unfold quickly and reliably so that I didn't waste time on setup. But it still had to be robust enough to support heavy steel plate. Since the operating depth of the bed is deeper than the base frame, I designed outriggers to extend the support of the base. They rotate into their deployed position with the help of a pop pin which engages into 1/2" steel plate. Floor locks at the outrigger ends prevent the whole machine from moving during operation:
Attachment 254906

Another key element to this design is a good set of main bearings. These 1.5" pillow blocks are positioned near the center of gravity of the moving components (bed + controller + optional downdraft assembly), so that it takes very little effort to rotate the bed:
Attachment 254908

The frame is 2 x 4 x 11 gauge tubing, tig welded and ground, and then finished with JAX blackening solution because I like that “old iron” look. (The moving “bed” portion of the frame is still raw steel, which you can see by the still visible grind marks in some of these images.) The whole frame should really get a top clear coat to protect against corrosion. I’m out in the desert, though, where rust isn't a big threat, so that wasn't a priority.

The base frame consists of 3 main pieces plus diagonal bracing, but feels as rigid as a 1-piece weldment.

The 3 rubber bumpers in the image below act as a landing pad for the back of the bed when it’s rotated into operating position:
Attachment 254910

A pop pin on each end of the lower portion of the frame locks the bed into its stored position:
Attachment 254912

After releasing the pop pins and rotating the bed, it ends up in this position, resting on the bumpers:
Attachment 254914

Heavy-duty custom cam locks are used to lock the front of the bed in its operating position. Here's one in its stored position, and then turned 90 degrees. That engages its hardened steel pin with a strike plate beneath the bed:
Attachment 254916

Not shown is that the handle of the above cam pivots up to give you leverage to easily complete the lock down. The rubber bumpers preload the bed slightly, so when you lock down these cams, the bed is really locked tight – no wiggle what so ever.

At the other end is the exact same thing, plus a shelf to support a plasma cutter. I’m using a fairly large unit – a Miller Spectrum 1000:
Attachment 254918

The slats on the machine are 3” x 7 gauge and supported by custom machined end brackets. The removable top plates (at each end) prevent the slats from being accidentally knocked loose when the bed is in its upright stored position:
Attachment 254920

For the CNC controller, I went with SteelTailor. I don’t normally favor Chinese tools, but this one had a good reputation with some other shop owners I talked to, and it’s cantilever design was the best fit for my Murphy concept. The other nice thing about SteelTailor, as opposed to most other controllers like Torchmate or PlasmaCAM, is that the computer is integrated with the controller. That not only eliminates the need for separate shop computer, but also power and connecting cable for the computer, a stand to set it on (or accidentally knock it off), and the inconvenience of one more thing to move.

That isn't to say that I was completely satisfied with the SteelTailor. I did make a few upgrades. One thing I didn't like was the excess mass of the cantilevered boom. I decided to lighten it to improve accuracy at full extension and higher cutting speeds. The first thing I did was strip out its Oxy-acetylene fuel lines. I planned to only run plasma, so there was no need for that extra weight. Next I fabricated a custom boom from 1.5 dia tubing that attaches to the top of the SteelTailor’s housing. This boom allows the main carriage to support the weight of the plasma cable rather than the cantilevered arm. Together those changes result in a lighter and more consistent load on the cantilevered arm, which eliminates any potential dip or sway.

A side benefit of the new boom is that it serves as a convenient grab handle if I need to reposition the carriage in the X direction prior to a cut or loading material.
Attachment 254922

The boom is also a natural attachment point for the cable chain that I added, which really neatens up the cabling:
Attachment 254924

Cable booms typically extend high over the table. Mine is horizontal so that I can keep everything within a small area after the fold. The loop of cable between the end of the boom and the torch is enough to provide plenty of Y-axis freedom without undue cable flex.
Attachment 254926

I also discovered that the stock SteelTailor wouldn't trigger my Miller Plasma cutter due to the SteelTailor's reliance on a low power relay and the Miller’s need for a higher triggering current. So I replace that relay with a higher capacity solid state relay. Problem solved.

Next thing I upgraded was the Z stage. The SteelTailor’s motor and rack and pinion drive were fine, but its guide assembly was sloppy. So I did some custom machining to integrate a precision linear slide.

My SteelTailor came with torch height control (THC) circuitry, but that only works when the arc is lit. I also wanted to sense material height prior to piercing. (Otherwise the unit has no way of reliably starting a cut on variable height material such as corrugated steel.) So I attached the torch to the Z stage using a set of pivoting parallel arms (horizontal aluminum bars in the image below) connected to a limit switch.

So lowering the torch until it hits the top of the material causes the torch to rise slightly and trigger the limit switch, which stops the Z motor. This gives me the option of inserting a couple extra lines of G code in the pierce sequence – e.g. lower torch until material contact is made, raise torch a prescribed amount, then pierce.

I also added limit switches to the upper and lower ends of the Z stage to protect against overtravel. All 3 limit switches are integrated into the Z stage, but you can see their lead wires in the image below:
Attachment 254928

TEST CUT
The slats are still virgin on this machine, but I did run a test cut (between the slats) to verify operation. I had my torch set a little hot for this test, but precision of the control is excellent:
Attachment 254930

UNFINISHED BUSINESS
There are just 4 tasks left on this project:

1. Wire in the limit switches (a simple cut and solder job).
2. Rewire the THC. In setting up the improved Z stage, I must have swapped the torch up and torch down wires, because under THC the torch lifts away from the material rather than lowering to it.
3. Blacken or paint the unfinished portions of the frame.
4. Cut and fabricate the downdraft plenum. I was planning to build a 16 gage sheet metal plenum w/ exhaust fan that attaches to the underside of the bed to collect slag and smoke. The machine’s frame is designed with adequate clearance for this plenum, which would rotate with the bed. See sketch below:

Attachment 254932


But then everything changed.

Due to unexpected circumstances, I’m moving in January and can’t take this baby with me. Anyone interested in taking over this project? No, I’m not giving it away, but I’d prefer to make someone from this forum a killer deal than sell it elsewhere. If you’re thinking about starting a build yourself or just want a good plasma table, make me an offer. I’m open to anything reasonable and don’t expect to cover my costs. However, you have to promise to update this thread with any additional improvements you make. :-)

BTW, I am keeping the Miller plasma cutter, but everything else goes including the SteelTailor and the FastCAM software that came with it. The software has never been loaded, and the SteelTailor hasn't been used other than for a few test cuts.

The machine is in the Phoenix/Tucson area. I don’t have time to crate and ship it, but I'd be happy to help load it for local pick up.

[Jason Crew]

Interesting.."portable" becomes "foldaway"...

[BTA PLASMA]

If only the steel tailor didn't double the width of that machine when its running the torch close to the rail. You went from space saving to requiring more than twice the room than the travel allows.

[rjengineer]

If only the steel tailor didn't double the width of that machine when its running the torch close to the rail. You went from space saving to requiring more than twice the room than the travel allows.

The SteelTailor does use more space during operation, but that’s true of many other types of shop equipment – e.g. infeed and outfeed for a band saw or drill press, or the extra circulation space needed around a table when welding or grinding.

In my 1-man shop, I seldom have more than a couple machines operating at one time. And with the exception of my Haas mill and larger material racks, most of my equipment is mobile. That allows me to pull whatever I need for the current job into the center of my shop, or push it back to make room for something else – e.g. my wife’s car.

[Eric S]

Interesting design. Looks like you did a nice job putting it all together.
looking forward to see how well it cuts.