what limits max speed?

[srmaietta]

Well I know that "leadscrew whip" limits things.. and I've read that on slower PC's the actual data output can limit speeds.. and I guess spindle rigidity will factor in there too, but is there a way to figure out max speeds when these factors are known? Steppers lost torque as speeds ramp up, so pushing it too fast will cause lost steps maybe?

For example my machine will be about 20"x20" (x,y) and will be using 3/8 acme 2 start 5 turns per inch leadscrews. NEMA 23 steppers. laminate trimmer spindle. Steel frame with aluminum and 1" thick PVC parts for the gantry. Ill be running mach3 with a P4 2.4 G machine.

Whats my limiting factor here? Any estimates on my max speed? I plan on mainly cutting hardwoods and engraving/drilling aluminum.

thanks everyone for any speed-related comments.

~Steve

[ger21]

You didn't specify motor torque, motor voltage and motor drives. Those would be the determining factor. But also, depending on depth of cut, the laminate trimmer might limit your useable speed as well.

Yes, the faster you go the less torque you have, but increasing the voltage can compensate up to a certain point.

[srmaietta]

Hey Gerry, I believe the motors will be HobbyCNC's 200 oz.in, 3v, 3a, 200 steps per rev. Plus their boards. (not sure of any specs on them)

12v 10A PS (seems low?)

anyway, I bought a kit and all this stuff is arriving any day now so I'm anxious to get it together and see what it will do. And where I can drop a bit of cash to see the best improvement. As we all are I guess..
thanks
~Steve

[ger21]

The cheapest improvement would probably be a 36V power supply.

[srmaietta]

An running the motors at a higher voltage will... Let them run faster? And then I guess I will start running into other limiting factors. Thats fine I just want to modify it a bit to get it running as well as I can with minimal mods. I can always slow it down in software.

Higher voltage PS -I was thinking that! according to this PDF http://www.campbelldesigns.com/files...ply-part-1.pdf
the PS amperage should only be about 2/3 the motors rating.

so.. 36 volts at around 6 amps?


thanks again!!

~Steve

[ger21]

Originally Posted by srmaietta .....the PS amperage should only be about 2/3 the motors rating. so.. 36 volts at around 6 amps? thanks again!! ~Steve

That 2/3 is a minimum. I personally would get about a 10amp supply.

[srmaietta]

Thanke Gerry, Im sure Ill have a few more Q's as the parts start filtering in, but we'll get there when we get there..

~Steve

[Glidergider]

Steve,
I haven't read that about slower computers. I've always been under the impression that slower computers are still plenty fast to drive CNC steppers.
Dave

Originally Posted by srmaietta .. and I've read that on slower PC's the actual data output can limit speeds.. ~Steve

[ger21]

Originally Posted by Glidergider Steve, I haven't read that about slower computers. I've always been under the impression that slower computers are still plenty fast to drive CNC steppers. Dave

Depends on the control software. While TurboCNC running under DOS can work with old ~200Mhz PC's, the speeds you get out of it can vary greatly with PC speed. Mach3's pulse rate is a constant 25,000 steps per second, but requires at least a 1Ghz PC. Mach3 also has 35Khz ad 45Khz modes, but those requre a 2Ghz or faster PC.