Plasma Cutter Gen 2 - Part 1: Introduction

by Joey Sacco on August 06, 2015

Welcome to the build blog for our second generation 5 x 10 CNC plasma table!

I have learned a lot with my first machine, that I started almost two years ago. With the machine, I have started a small business, and eventually quit my job to pursue this full time. I have cut TONS of metal, literally, with the first machine. Now, it is time for my second full build, designing it with everything I learned about the first machine. Sorry for all the wording. If you do not like reading, move on and complain elsewhere. I am going to include a lot of information that I wish I had known during the build of my first machine.

Now, sit back, grab a few beers, and read on!

A little background on the first build:

– Why: I wanted to use a belt drive because of quiet operation, and zero backlash. I ran the belt around a pulley fixed to the shaft of the stepper motors in direct drive.
– Why it sucked: There was no way for me to measure the belt tension easily, since I have no sort of tensiometer to do so. I could have probably made one using a dial indicator, but never did. The tension must be the same on each side, because if one side is stretched further than the other, the teeth per inch will be different, making one side track faster than the other. After two years of use, stretching occurred, and in a non-uniform manner. The pitch was variable down the length of the belt, making it impossible to make parts within a proper dimension.

– Why: It’s easy. No pillow blocks, additional belts, cutting slots on the mill, etc.
– Why it sucked: In my application, the speed was great and never did the gantry stop due to missed steps. However, having the pulley in single shear on the motor shaft led to some issues. After applying tension to the belt, it created a large stress concentration on the motor shaft where the flat portion of the shaft met the round portion. I actually snapped two motor shafts at this point on two different occasions. Of course, it always happens while cutting a job.

– What I went with: I used 2″ square tube as my slides, paired with skateboard bearings. On my Y axis, they worked great. On my Gantry, I could not keep my carriage from walking in the Y direction as it moved from left to right in the X axis. I beefed up the carriage, and added more bearings to increase surface area and prevent it from rotating about the axis Nothing helped. In the Y axis, it was fine, since the degrees of freedom of rotating about the axis were eliminated due to the opposing carriages at each end. Also, I made the linear rails raised up, vs being level or lower than the cutting surface, this kept the rails out of the dirt and splash zone from the cutter, but also prevented any side loading of the machine. In addition to having the slides up high, I also did not account for the offset of the torch from the gantry, and therefore lost travel in my Y axis by ending the rail at the backside of the table. I could have resolved this by either extending the table and rails further, or just extend the rails past the table.

– Choice of manufacturer: I went with an Everlast PowerPlasma 50 unit due to the low cost, and support for CNC. This was a HUGE mistake. Not only do they not provide any guidelines for where to run your machine at (think: inches per minute, cut height, amperage, arc voltage for torch height control), I was told by the company that this machine was not intended to be used on a CNC machine, though it comes equipped with a CNC port, and advertises that is is CNC ready on the website. I burned out 3 different PP50 units in the process of trying to use this thing. With a hand torch, and eventually after purchasing a genuine Trafimet machine torch.
– How it was resolved: I finally gave up on the machines, and was tired of them literally going up in flames, that I plunged for the Hypertherm Powermax 45. I should have just done this from the beginning. I have used this machine for over a year, and have yet to have an issue with it. All the stories about how superior Hypertherm is are true.

– Choice of manufacturer: I chose to use a hobbyCNC board for the first go around. I was sitting at work one day, hating life, and looking around for a CNC kit. For just a little over $300 I got a 4 axis board (needs to be soldered) and 4 stepper motors. That’s what literally started my first build. The board eventually burned out on me, when I replaced it with the Gecko G540, which has been absolutely trouble free.

– What I did: I made the water table using 1.5″ angle around the edges, creating a frame. Then I welded a sheet of 15ga to the bottom, making a tray. I only stitch welded it, to prevent warping. Yeah, it happened anyway. I sealed the remaining gaps with silicone, and then painted it with Rustoleum paint so I can get cutting. I added 1.5″ x 1/8″ slats to cut on, which were held in by bending them, allowing the spring force of the steel to hold them in place. I suspended the slats 1/8″ above the table to allow water to flow beneath. I have used it since the beginning and never had a leak.
– What sucked: After cutting a bunch, the water would not flow under the slats because they gaps got clogged with metal gunk. The paint peeled off within a month or two, because it is not designed to be submerged for long periods of time. The warping of the 16ga was terrible, and it actually pushed up on some of the slats.

– What I used: I went with 2″ square tube with 1/8″ wall to built the table frame.
– Why it sucked: Now, this was plenty heavy duty to hold the weight of anything I would be putting on the table, however, when a heavy gantry is slinging around during cuts, the table shook all over. I eventually welded in X bracing in the sides, and installed more bracing underneath to eliminate it. You may ask, “Who cares if it shakes?” Any shaking will translate into shaky cuts. To fight it, I had to slow the acceleration of the gantry down significantly, which then translates to rounded corners vs sharp corner.

– Why I did it: It looks cool. All the professional machines do it.
– Why it sucked: It acted as a weight that would move around as the gantry moved around the table. The professional machines (I mean the really expensive ones that look like a solid piece of metal) weigh TONS, and do not care if a computer is mounted to it. Before I braced the table further, you could feel a lot of motion translate to the monitor stand, thus sending more vibration back to the table, and eventually into the torch.

– Is it necessary? You betcha! I ran without one for about 4 months and the machine consumed more nozzles and electrodes than I did beer over the frustration. A torch height control is ABSOLUTELY necessary for your plasma cutter to perform well. When the tip of the plasma cutter hits the workpiece, it shorts out, and you can see the damage when you pull the electrode and nozzle out and look inside. Consumable life went up ten-fold after adding a torch height control. I used the CANCCNC Low Cost Torch Height Control (LCTHC for short), and will do so again on the second build. It’s cheap, and it works.

Now, if I have not put you to sleep by this time, I hope that if you are pursuing a CNC Plasma build, that perhaps I have shared some useful information to save you time, money and frustration down the road.

Stay tuned for the build.


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