There still are benefits to servo motors on machines with less than perfect mechanics. Speed. If you somedays need to cut at 5ipm on 1" material, than an hour later cut at 380 ipm on large parts without too much intricate detail....the servo has torque at both the low speed and the high speed, the stepper only has torque in a narrow band...can be high speed or low speed, but not both. Most stepper machines are limited at the top speed....the most popular ones stop at 150 ipm. Servo machines typically can go to 400 ipm.
Next, since servos have an encoder feedback loop....it is unlikely you will lose position even with collisions. Further, the software can take advantage of knowing where the torch is. Push the gantry out of the way to inspect a part, then hit the start button and it will move back and restart cutting right where it stopped. The stepper will start where you pushed it to. And, often you can highlight a part, hit copy, drag and drop it where you want on the plate. Much more difficult to do this with a stepper machine.....re-zero, do some x-y coordinate math....and if you didn'd makje a mistake the new part will be in the right place!
I am not knocking steppers. They have a perfect fit in the world of light industrial and entry level machines where the complexity and cost of servos is sometimes prohibitive.
Don't expect any machine that mechanical guideways that are less accurate than a recirculating bearing mounted on a stress relived milled surface...to be as accurate. On $100k industrial machines you will only find recirculating ways, stress relieved milled ways, servodrives, etc. That is why they cost so much.
You can develop specs for a Hypertherm plasma for low speed cutting....you will have some dross (easily removed) but perfectly smooth edges even on thin materials. I do it on my Plasmacam all the time.
Jim Colt
Metriccar wrote:For comparison purposes, these 1" high letters were cut at manual settings using fine cut consumables, 14 gauge. 220 IPM. The only difference is the one on the left, .05 for acceleration was used, while on the right, acceleration was at .40.
You can see the heat discoloration (and this translates to dross on the backside, as well as warping on bigger higher detail cuts), but the machine held control a lot better.
Until a machine can cut in this detail, with high speed and acceleratoin, 1) I don't see the benefit of "servo" motors if we have to run acceleration so low anyways and 2) very low amp plasma cutters would be ideal for thinner metals, which was one of the reasons I was interested in the Powermax30 XP. I have a funny feeling a lower amp plasma cutter will be a lot cheaper than any gantry/table that can maintain control at these high a speed. Those big machines like AKS Accu-Kuts have gantries that weigh probably as much if not more as my entire Plasmacam weighs. There would have to be a lot of engineering and tight tolerances (ie expensive) to be able to compete with me just lowering the acceleration on my entry level machine.
And until one of these Mach3 table manufacturers can show they can cut as stable an "E" on the left at a higher acceleration rate, I see no point in switching to a Mach 3.
photo.JPG
. The lean coming out of a corner has always been quite pronounced on the thick stuff.
