CNC Plasma Cutter, Laser Cutter, Water Jet

[antsals]

Does anyone know what the construction is like on an "industrial" CNC Plasma Cutter, Laser Cutter and / or Water Jet Cutter? I'm currently trying to workout the best way to drive may gantry on my plasma cutter bed, but thought a good place to start was the "industrial area"

I know there are a few options but looking at a few pics of the industrial stuff makes it a bit easier to understand and design.

My thoughts are ballscrews but I'm thinking that might be overkill a little. A lot of designs I have seen on the forum use rack and pinion, but I'm worried with that around accuracy......maybe just a leadscrew but I'm worried that will bind on acceleration?

Any thoughts would be good.

Cheers
Ant

[magma-joe]

antsals,

I would agree that ball screws are over kill. Another factor to consider is the extremely dirty enviroment drive components operate in. Rack and pinions are much more forgiving than ball screws. In addition a 10' table with dual X drives would not be practical for ball screws. Perhaps they are more suited to a 2 X 2 like the Torchmate? YouTube - DSCF1144.AVI

The majority of industrial table builders I have seen are using rack and pinion. A few incorporate a belt drive system with their tables. I have included a link to a company called Retro Plasma. They build industrial plasma tables. You can zoom in for some closeup pics of all their tables in the PDF pictures they provide for each model. They do make some nice machines.

http://www.retroplasma.com/documents...D%20slides.pdf

MINI HORNET HD CNC plasma and oxyfuel cutting machine

This company uses a belt drive on the X axis and a rack and pinion on the Y.
http://www.fastcutcnc.com/

Magma-joe

[antsals]

Thanks for the information. How do they cope with backlash issues on the rack and pinion?

Thanks,
Anthony

[magma-joe]

antsals,

There is no back lash in the rack and pinion systems. The pinion is preloaded with spring pressure or a pneumatic cylinder to eliminate back lash.

Magma-joe

[jimcolt]

There are of course many different designs on industrial cnc plasma machines....at my last count there were 85 manufacturers worldwide.

Ballscrews are not what I would call overkill, however they have their limitations when it comes to cost, practical travel length, as well as with inertial matching (it is tough for a motor to accelerate a large, heavy ballscrew) although I have seen a few designs that spin the nut instead of the screw. If I was designing a 4 x 4 table with ultimate precision (and I have done so) I would use intertia matched, direct coupled AC brushless servos with ballscrews. The balscrews need to be protected from dust.

Plasma works best with 1. very smooth motion, 2. the best possible acceleration and de-acceleration 3. perfect height control

The vast majority of industrial plasma cnc machine use linear recirculating bearings and rails (like THK brand) on both axis, use rack and pinions (better machines use helical rack and pinions) and some method of accurately maintaining the pinion depth for good motion and minimal backlash. Almost all high end industrial machines use planetary gearboxes with low to zero backlash, and virtually all use AC brushles servos that are properly inertia matched for best acceleration. Many systems use fiber optic communication with the servo drives (from the cnc) such as Sercos. Almost all high end industrial systems use a PC based, industrially hardened plasma specific motion controller such as the Hypertherm Edge Pro, or a control from Burny.

Industrial machines generally cut the same part as their lower cost entry level cousins....however the industrial machines are designed to be very large (I have seem 50' x 350' travel) and are able to maintain high duty cycle, 3 shift a day 365 day a year cutting for 10 to 20 years with minimal downtime....which means they are of heavy construction, and cost is not of the highest concern.

Jim Colt Hypertherm

Originally Posted by antsals Does anyone know what the construction is like on an "industrial" CNC Plasma Cutter, Laser Cutter and / or Water Jet Cutter? I'm currently trying to workout the best way to drive may gantry on my plasma cutter bed, but thought a good place to start was the "industrial area" I know there are a few options but looking at a few pics of the industrial stuff makes it a bit easier to understand and design. My thoughts are ballscrews but I'm thinking that might be overkill a little. A lot of designs I have seen on the forum use rack and pinion, but I'm worried with that around accuracy......maybe just a leadscrew but I'm worried that will bind on acceleration? Any thoughts would be good. Cheers Ant

[antsals]

Jim thanks for the detailed information. So in your opinion you would see no reason why I couldn't use a ball screaw to drive the gantry. Each option is as good as the other? My travel is only 1500mm and to be honest I don't think I will get anywhere near the industrial feed rates.
I'd planned to cover the ball screw to protect it anyway.

If I was to use a rack and pinion the post above mentions pre-load of the pinion to eliminate the backlash. Does this need to be at an angle to the teeth or could you get away with the load acting directly down?

Thanks Again.
Ant

[jimcolt]

It all depends on how much you want to spend, and what you have/need for accuracy goals. 99.9% of the cnc plasma machines built in the world use standard, straight tooth rack and pinion gears. They are reliable, accurate enough, and are the lowest cost option in most cases.

Helical gears are much pricier and harder to set up (alignment and depth of the gear teeth are critical.

Ballscrews require more engineering....the loads imparted on a ballscrew will cause the screw to twist....which can throw off accuracy.....to counter this larger diameters are specified (with longer lengths and bigger loads), and when larger diameters are required, the drive motors also need to be upgraded in order to maintain decent accleration numbers. Spinning a long heavy screw takes some torque and acceleration capability! The nice thing about ballscrews are that you can eliminate gear reduction, the bad things are listed above, and ballscrews and larger motors add a lot of cost. Probably why you don't see them used often!

What kind of accuracies are you looking for? What type of plasma system are you planning to use? An air plasma is the least accurate plasma, yet is low priced. A high definition class plasma is the most accurate, yet is at least 10x the cost of an air plasma. I see no need for ballscrews or helical gears when an air plasma is used.

Jim Colt