3.5X1.5 Meters cnc plasma cutter

thefabricator03 wrote:

Tom,

Do you have any experience using large stepper motors on a large heavy plasma gantry?

If so how did you find their performance?

Not really, this is the biggest gantry i did, but aluminium so something like 45Kg in total, and i would not consider that heavy.
I did retrofit some hefty industrial ones with metal gantry weighing in at over 300Kg, but it uses two smallish servo motors on both sides.
From experience i tend to avoid using Nema 34 if at all possible as i did use them on a 3m metal gantry, without very good drives that do proper microstepping it was just to much vibration. It was something like 70Kg, if i remember correctly.
I am sure with some decent gearing and good drives it can be done and work properly. Just avoid the normal rack and pinion they do cause a lot of vibrations, use helical ones.
FYI, i do test how much the gantry can pull in Kg and this one with small motors that you can see in the video did 12Kg in the middle of the gantry before stalling, same drive same power with the motors that are now in (the 110mm long ones) it does 21Kg. That is more than enough for a plasma, even if something goes terribly wrong, the gantry can not be bent. Having 200Kg of pulling force on a plasma is overkill.

tommylight wrote:

Having 200Kg of pulling force on a plasma is overkill.

There are no cutting forces, but you might want to be able to turn tight corners at high speed?
20kg on 40kg gantry is only 0.5g accelleration.

I have it set at 500mm/s/s for now, did not test it further. Usually i never require more than 700mm/s/s.
But the Z axis is set at 3000mm/s/s!
There are going to be some 5 to 10Kg added with the drag chain and the side plastics, then i can see if it needs more. The drives are set at 1A for the two gantry motors, i have plenty of power left in them as they can do 4A RMS.

This went to a new home yesterday, despite some drawback on the way, like me falling off the truck and them yanking most of the cabling while putting it in its new place.
Today went and put back the cabling, checked and double checked, turned it on and all is good.
After wiring the Plasma source and THCAD had to adjust voltage and float switch distance, min and max arcok values and soon enough got it cutting like a champ, thc tracks perfectly, there is very little to no dross under the cuts, all in all, very happy.
Using the toma_thc config with the added comp for THCAD, only voltage from THCAD although i had already installed provisions for ArcOK in the plasma source. I have the servo period set at 500000 so the reaction time is very, very fast and there is no "bunny hopping" at all, most of the time the UP and DOWN inficators on the GUI remain off during short adjustments.
The THCAD is wired directly to parallel port, base thread at 20000 with no latency issues, seen the voltage go up to 286V when it went of the material for a short period of time.
Now a big thank you is in order for PCW for providing us with such great electronics equipment and PCW, i need some more THCAD like yesterday !
When it gets it's clothes on, i will post some more pictures.
Thank you, all.
Tom.

Did a quick test last night by cutting 30Cm up and down on a 7Cm slope at 2m/min, perfect clean cut ! Damn, it tracks fast!
The Proma THC150 could also do that but setting it that fast would result in bunny hopping when cutting leveled plate. This does not hop, at all. The adjustments are very fine and very fast.
I have not been this happy since i built my first radio when i was 8 or 9!
I have to order some more THCAD, most probably one of each version and spend some quality time with them. For the moment i am also out of plasma cutters, except 2 non functional ones and no time to build a HF/HV start for a Thermal Dynamics made out of 4 X 35A sources stacked together, and the nozzles are over 120$ for a set! But i did find a used Hypertherm Max43 for 400 Euros, so i might get that to play with, again expensive consumables, but i wont be cutting much with it.

rodw wrote:

Tommy,

I'm a bit lost here about the electronics you are using. So you are using a THCAD but are you also using a Mesa card?
I thought you said you were using a modified Proma config with an up/down module?
Have you tried Plasmac?

On this one THCAD wired directly to parallel port, no other Mesa cards. THCAD is set at 1/64, although i did test it at 1/32 and it worked without a hitch up to 125V, the reason being better interference immunity at the cost of lower resolution.
I am using the config used for Proma with the addition of the comp that PhillC graciously wrote.
I did try the PlasmaC on this machine and it also works properly, but since i will not be using the machine i have to use the old config as it is simpler and has less things for the user to fiddle with.
Hopefully i will be building a machine for me ( dream on ... ), and that is for sure getting the PlasmaC treatment.

thefabricator03 wrote:

If you can spring for a machine with RS485 you will never need to touch the front panel of the plasma unit again!

Oh i can do that on machines without RS485 for sure, using relays and D/A + A/D converters and have total control !
As Pink Floyd once ( or more times ) said : TIME !!!
Proof:


Well that is the thing i lack most !

Here is the video of it cutting 5mm wall metal tubing under water, even the torch is mostly under water and it starts and cuts perfectly.