Fast Printing and Motors

I've been experimenting with printing at 150-250mm/s with the current Marlin. Should I be concerned about the motors at these speeds? I know the movement is smoother with acceleration, so they aren't having to jerk everything around so much. With typical Nema 17 steppers and a gantry setup (no bowden) should it still be well within the motor's specs to haul around the extruder at 250mm/s?

The motor's specs are on this page, model SM42HT33-1334A,

A reasonable maximum speed for small steppers is ~1000RPM, you probably won't get anywhere near that with 12V driving the stepper.
Assuming they are inside a reasonable thermal envelope, the only thing you really have to worry about is too much torque ans with that they just stall.

edit: late night. high rpm is possible at 24v. this motor specs12v 1500 pps, 200 pulses per circle=7.5 times per second or 450 rpm.

Edited 3 time(s). Last edit at 09/27/2012 06:49PM by jamesdanielv.

you said you have been experimenting, so did u try 250 mm/s? If you are lookiing for a anilitical answer you can calculate it out based on mass of the system, motor rpm, etc.
What im saying is if you already have it built test it, when you miss steps you know that is to fast, from whatever that speed is reduce it by a safety factor and that should be your max speed.
Consider using more Voltage to get more speed, i use 24V.

My limits are clearly with extrusion rather than XY motors. My extruder is direct drive with a Nema 17 motor going into a Makergear hot end, with 1.75 filament and .35 nozzle. With PLA at 190 and ABS at 210 I'm getting skipping at 150 on lines long enough to hit top speed. Would adding a gearbox make any difference? Or does it all come down to the speed of melting?

I could go hotter with ABS, but would need to add a fan to protect the PEEK insulator since it will melt at 250C. Is it more important to have a longer melt zone? Or do you need more intense heat in a smaller area at the nozzle?

Also I'm noticing while printing infill, the extruder motor is turning at an RPM that is equivalent to 300mm/minute, and skipping. It is capable of extruding at 500 or more manually. Is this speed of rotation I'm seeing during the print actually an average of much faster moves and pauses that are requiring more force than the motor can deliver?

Edited 1 time(s). Last edit at 09/27/2012 01:19PM by IanJohnson.

At some point the hobbed bolt will just eat the filament, and you need to reduce the back pressure, either by running hotter, or using a hotend with less back pressure, the arcol hotends are supposed to be good in this regard.

I might try to make an Arcol work. The Makergear's low operating temp is a bit limiting if you want to try other materials like Polycarbonate.

In the meantime, would a .5 nozzle reduce backpressure significantly? Is there much of a tradeoff in detail between .5 and .35?

Yes there is a MASSIVE difference in back pressure between 0.35 and 0.5mm nozzles.
You'll get less square corners with a 0.5mm hotend and at lower layer heights, you'll have to use larger w/h ratios.

IanJohnson, give me your address in private and i will make for and send you a diamond tooth knurled bolt. i want to see how fast it works for you! i use it at 80-100mm/minute flow rate on my ultimaker.

james