Sounds like a very interesting project indeed - I am looking forward to hearing more about this as you progress with the build.

Tweakie.

 

I am also building a CNC plasma cutter. I have the frame built from a purchased set of plans. The plans call for just V rails and V wheels for both sides of the gantry's Y Axis driven by racks and gears on the steppers . I'm told plasma cutters produce a significant amount of fine steel dust. I'm wondering if anyone has a comment about what type of open builds linear motion pieces would be best for this application. I'm worried about the dust gumming up the works.

Thanks!

 

Thanks for the information about belts. I guess my main concern is about what kind of bearings would be best for the X and Y axes to run on. As I mentioned, I'm worried about the bearing system getting clogged with the dust.

 

First of all, your welding. If it is structurally sound, in this sort of environment who cares. Actually if you paint it or have it powder coated it will help hide what YOU don't like. If you are going to be doing much of this sort of welding in the future, consider getting a mig wire welder. It makes welding for us "hacks" much easier. Now a question if you don't mind. Who did the plasma cutting for you and how much did it cost?

 

looks great from here ive been welding all my live as long as it holds who cares
of course I have two migs and a tig welder
what are you going to use for a plasma cutter im using a simadre d5o its black and so far its doing great the trick is to and a ground from the torch tip to the work
I bought a 65 dollar machine torch of ebay it was the same brand as the hand held that came with my plasma

 

Yeah, if you're not going to use it very often, argon can be a hassle. The strange thing about argon (at least in my location) is that it costs only a small percentage more to get a large bottle filled than one half its size. There is really nothing wrong with flux core wire welding. I find it infinitely easier than stick. Of course the only way to get good with any welding technique is practice, practice and more practice. But that also may be because I'm not the most coordinated guy around. The only downside is the flux forms slag that you have to chip and brush off. Another plus with many flux core wire machines is, that as delivered, they can only use flux core wire, but at a later time can have the extra goodies added for actual mig.

 

Good fortune with the build - I am looking forward to watching your video

Tweakie.

 

OK, I'm looking for an opinion now. Given a choice which of the three drive systems would be best for a 4' X 4' plasma cutter?
1. Acme screw or the like
2. A drive belt with the stepper mounted at the ends of the rails
3. The "traveling stepper" where the stepper is mounted on a trolley with the drive belt looping up over the gear on the motor.

Also for each option, how much torque would the stepper motors need, particularly the two on the Y axes driving the gantry.

 

Acme screws are pretty much the standard here for use in environments that are dusty or dirty. The squared off teeth of the screw help to keep dirt from accumulating and help to insure that what does collect can fall off/out as the screw turns. Mounting a brush on the gantry to follow the screws as the head moves is cheap insurance against dirt. We have lots of commercial laser cutters and plasma cutters in the plant and none of them use belts. There are a couple with VERY well protected racks/gears, but the overwhelming majority use large acme screws.

For your steppers, I'd use NEMA 23 270 in.oz. in the 2.4-3mh inductance range. I believe the lower the inductance, the more torque/speed you will have. If you elect to go with Acme screws, get "5 start" for better speed, if you can. For instance, a single start 1/2" 10TPI Acme screw must rotate 10 times to move your gantry 1". A 5 start Acme screw will move that same gantry 1/2" for each revolution. If you make the mistake of getting steppers with too high a inductance rating, you'll find that even a high torque stepper will stall out or run too slowly. Higher stepper operating voltage is a good thing too.

 

I appreciate your thoughts on the matter. Your statements about stepper motor inductance are right on the money. Even having been educated as an electrical engineer, the influence of inductance had never crossed my mind (what little is left of at my advancing age, hence my avatar). Here is a link to a succinct explanation of the issue.

http://www.nmbtc.com/step-motors/engineering/torque-and-speed-relationship/

One more question, if I may. Do the number of starts effect the need for backlash protection? Also I assume that for screws that are going to be in the 1000 to 1500 mm range, 1/2 inch diameter is probably a lower limit in size, true?

 

Any updates on this build? Would like to see it cut!

 

Nice build,

Looking for the plasma torch assembly.