[Galane]

I'm going to be designing and helping build a large plasma table, around 5x10 feet to accommodate full use of 4x8 sheets of steel. Mostly what will be cut is 1/4" and 1/2" plate to build new housings for refurbished pellet mills.

The original housings on many of these mills were thinner than 1/4" and have not withstood the test of use. Some come into the shop with more patches than original housing.

For the drive on both axes I'm going to use stationary chain looped between a drive sprocket and two idlers. A cross shaft will keep both sides of the gantry moving together. Extreme super precision isn't a primary goal, thus V groove wheels running on angle iron should be good enough. Most parts to be cut will be measured in feet. The main thing is to have better accuracy and cleaner cuts than the old pattern follower gas torch and to eliminate the need to make a new template (1/8" smaller all around) for every new part, many of which end up being one-offs so the pattern ends up in the scrap bin.

Watching many hours of video on Youtube of commercial and home/shop built CNC equipment, reading forums and subscribing to the LinuxCNC email list has provided a ton of ideas and useful info which should help prevent making errors and falling into various pits of wasted money doing things that don't work out.

I've also been researching various kits of motors, controls etc. Looks like for the money the front runner is the CandCNC Dragon Cut with 620 oz motors, mainly for the integrated THC. Looks like the perfect system for a first CNC build instead of diving into gathering pieces from here and there and trying to make it all work together.

What I'm wondering about that kit is how tricky is it to slave two of the motors to one axis so I can still have two axes free for a possible 5 axis upgrade? The recommended gantry weight for that kit is 100 pounds, this table may hit or exceed that weight. With a shop full of steel, steel is the construction material that will cost the least. I'm figuring on some strategic use of lightening holes to save some pounds. Aluminum is simply right out for this table, it's going into a shop where forklifts and very heavy cast iron hunks of pellet mills get moved about, and what would be a minor bump from a 4x8 half inch sheet of plate to a steel gantry or table frame could demolish or at least badly damage an aluminum one. (Coming up with a way to load the big sheets easily is going to be its own challenge!)

For ganging two motors on the gantry, I'm envisioning coupling them together with rotors aligned, control from one output going to two drivers and using encoder feedback from just one of the motors. Possible?

Or instead of ganging motors in tandem, can I get that kit with one more powerful motor? I've done some searching on ganged/slaved/tandem steppers and found plenty of troublesome setups. Of course the ones that work without problems are the ones discussed least.

As for adding 2 axis torch tilt, I've come up with a design that I haven't seen in any video or still image of a gantry machine. I see them twisting around, winding up the hose etc then having to unwind. No twisting with what I've come up with. Nor will this design have to mount the torch way out to make room for X direction tilt. I'm planning on building the gantry in a way to make the upgrade possible, hopefully rather simple, without having to do major modifications. Just did some more searching, google and this forum. So far nothing like my idea. It'll be a back burner concept until construction of the table is under-weigh.

[plain ol Bill]

Slaving two motors is a piece of cake in Mach using CandCNC products. A matter of just telling the software about it and you are done.

[Galane]

Is that slaving two axes or two motors controlled by a single axis output? I want to keep the possibility of adding 2 axis torch tilt later on.