Plasma cutter advice please!

PowGe has an ebay store and has pulley's there too in case anyone is looking for this brand.
one thing to note is the 2GT belts in the 15mm width range are not steel corded and the pulley's for these only go down to 24 teeth.

that is what i have been using as well. never had a problem with them except the one time i acutually ripped the 10mm shaft off of a nema 23. the kevlar ones on the other hand, total crap. they also have a store on amazon a bit more expensive than ebay, but you can get them cheaper. give and take

yeah on the Ebay store they had a 10 meter belt package with 10 24 tooth drive pulley's as part of the deal for around $100. It would have been nice if they had idler pulley's too but i seen nothing in that department unfortunately.
So with a 3mm pitch belt and a 24 tooth pulley you get a pretty quick rate of travel at low speeds right out of the gate. only down side is you need some pretty fine micro stepping to deal with it. which this particular machine lacks at the moment so bigger motors and better drives are on a long wish list.
So as long as the belts are good you save around $600 to $700 vs Gates belt's. They are out of their minds only selling 50 feet or more at a time at $13 to $14 a foot

machinedude wrote:

So with a 3mm pitch belt and a 24 tooth pulley you get a pretty quick rate of travel at low speeds right out of the gate. only down side is you need some pretty fine micro stepping to deal with it. which this particular machine lacks at the moment so bigger motors and better drives are on a long wish list.

that is exactly what i have been using with good results.  i am thinking right now that i am going to put a 3:1ish reduction on it but right now i am having a hard time finding 60t pulleys that wont break the bank.  they are seriously wanting $45+ each for them.  

machinedude post=288009 userid=25766
So as long as the belts are good you save around $600 to $700 vs Gates belt's. They are out of their minds only selling 50 feet or more at a time at $13 to $14 a foot

yes that is absolutely ridiculous!  the only time ive used gates belts were some closed loop gt2 belts on a 3d printer and i noticed exactly 0 difference in lifespan or performance from other brands. 

quick question for @tommylight.  how do you handle your touch off on the z?  i was thinking of using a spring loaded switch on some simple rails using the torch head as the probe, but is that overkill?  or is there a better way of getting material height?

and @pcw, how come mesa doesnt make a voltage divider?  i was going with tommy's advice and going to use a pair of resistors, but with that much voltage, it just really makes me nervous.  i picked up a thcad2 and i would like to mount it inside of the control box, so i want as low of voltage as i can get to come out of the plasma unit into the controller.  i have enought space on the back of the unit to put a pair of avaiation plugs on the back of it, one for the switch and the other for the thc, but that still makes me leery having that much voltage come out of the unit, especially how cords and cables seem to get snagged and pulled in my world.  even with a box on the back like tommy said, i would still prefer to keep as much as i can inside the box if possible 

here is something i did not really pay much attention to but is important, with belt drives since they move so fast and needing micro stepping to get a good resolution the input frequency of the dives vs your micro stepping rate play a big factor in your rapid rates.

gear reduction helps with the torque and reduces the amount micro steeps needed to get the same resolution and also takes some of the requirements off the input frequency of the drives.so it can save you some money on more expensive motors and drives that can handle this.

from what i have seen the Mesa card are above and beyond this limit so i think the drives are the brick wall you hit first.

just to give an example a 3mm pitch belt running with a 24 tooth pulley is moving 72mm per revolution so to get in the ball park of a .0001 resolution imperial you have to micro step at around 40,000 per revolution with a 1.8 degree stepper. if the drive tops out at 500KHz per second it can only handle 12.5 revolutions per second and with max out at a750 RPM and puts you over 2100 IPM for a rapid rate

i doubt plasma application demand that high of a resolution but things to think about in the design process regardless i don't recall seeing much on the subject in any detail so it's worth the mention.

tommylight wrote:

Just went over my topic on building 2+2+3 plasma machines, i was sure i posted pictures of new Z axis insides, i did not! Shame on me!
Here is the old versions
www.forum.linuxcnc.org/show-your-stuff/3...uild?start=40#166228
I will try to make some time to disassemble one of the new ones and take some pictures... do remind me if i forget.
 

so i am assuming that the sensor there is your z max.  how are you setting your torch height?  and that is a very clean design btw.  that 17 has enough torque to lift that entire head?  langmuir has an interesting way of doing it, and i was thinking maybe something along these lines 

machinedude wrote:

here is something i did not really pay much attention to but is important, with belt drives since they move so fast and needing micro stepping to get a good resolution the input frequency of the dives vs your micro stepping rate play a big factor in your rapid rates.

the machine i am using most of the hardware from is running 425oz/in nema 23 steppers driven by dm420y drivers @36v.  since i switched to the digital steppers, it is night and day difference in the performance and noise.  before my budget only allowed me to use tb6600 drivers and while they get the job done, they are kinda crappy really.  it is directly driven by 3m 24t pulleys and the base i have it on is my limiting factor because it is not very stable really.  like i said, it was an old design and was built before i learned alot of things and really learned to think big.  but all of this will transfer over directly to my plasma table.  i was going to go with ballscrews, but tommy talked me out of that which is good because i have a lot of 3m belt stuff lying around.  and rod conviced me that i should go with a reduction.  im thinking 3:1.  i am also in the process of building a 4080 router to replace this one and it is going to be helical r&p, so i will probably go with a 3:1 reduction on it as well.  that way i can buy the pulleys in bulk hopefully.  as for the overall rapids tho, even with what i got its pretty snappy.  it will make the entire table jump when it takes off.  yeah, lesson learned.  the next bases will be built like tanks!