[janz99]

Hey guys, I've been a long time lurker of this site but I don't make many posts. I am considering building a CNC plasma table for my own personal hobby/use. I bought an old Quincy 325 compressor that I am going to be rebuilding in hopes of using it for the plasma cutter. I was curious as to how the smoke would be using a water table plasma? It will be going into a double car garage, so the space is fairly small considering. Should I be looking to put a large exhaust fan in before I get started in order to deal with the fumes/smoke?

Onto the design considerations. I have an OK grasp on how the machine works, but there is a few details I am unclear about. The whole floating head design is a bit of a mystery to me. This was the best video I could find showing somewhat how it works:



So when a cut is being made, the plasma torch and head are literally held down by gravity alone? What is the advantage of having it float like this as well as having a moving z axis?

The other question I have is in regards to rack and pinion motion versus synchronous belts. The rack and pinion looks more robust, but might be affected by debris depending on how it was mounted. It would also need some sort of automatic tension to keep the backlash to a minimum. The belt system looks "cool", but what is the advantage to using this system of the rack? I would be concerned with the belts stretching causing off positional errors as its accelerating/decelerating?

I am in no rush to build a machine, as I have a few other things to deal with in preparation for the project, but I would really like to get started on designing/modeling it. My idea was to make a 4x4 table, that could be upgraded to something larger down the road if needed. I was hoping to incorporate some form of pinning/locating so that If I had to do something larger then 4x4, I could index a sheet through the machine. Thoughts on this idea? Is there any features that you would have incorporated into your machine that you didn't at the time of build?

As for budget, I was hoping to keep it under the $5000 mark with the plasma cutter. I would like a fully welded frame with water table, and 3 axis motion, with torch height control. Is this budget reasonable for something along these lines?

Thanks
Ryan

[janz99]

No one has any input?

[flyinwilly]

The floating head is used to find the work surface before starting the cut. As the Z axis moves down to the work surface before the cut, the torch contacts the surface, the floating head moves up slightly and trips a switch which tells the system that the torch is at zero height. The system then moves the torch to pierce height (whatever you've set in software) and you're off and running. It will do this before every pierce. There are other ways to find the work surface but this is a simple and reliable way to do it.

As for smoke and fumes, there will be plenty if you don't exhaust them somehow. I had the same problem and incorporated a downdraft system (along with the water table) in my machine. See my build at " A Different Machine - Downdraft/water table " and you might get some ideas. I've read here on the Zone that some folks have used a overhead fan with some success so you can get some ideas from them. One other thing to consider is that these machines generate a lot of dust (i.e. the sparks you see flying when the machines are cutting). The water table will trap most of the junk but not the stuff above the plate. Because you are running in a small space, you may have to enclose that area to keep the dust from spreading. One other thing to remember is that the dust is magnetic because it is basically tiny pieces of metal.

I also use a belt drive and it's been no problem and I've been running for 5 years with it. I think it is a lot less expensive to build than a rack but you'll have to decide when you finish you're design. My gantry is fairly light (approx 20-25 lbs) so the belts work fine. They may not work as well on a heavy gantry.

Good luck with your build.

Willy