Actual speed versus planned speed
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For what it's worth I'm planning to pledge for one of your extruders. I am curious though, and I'm sure this isn't the place to ask…but how do you deal with any torsional spring effect of the cable between the motor and drive gear? Surely there must be some energy being stored in the twisting of the drive cable. Doesn't this effectively behave similarly to the elastic properties of filament in a bowden tube?
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You can also mount a volcano and 1.2 mm nozzle on your extruder.
If you extruder can push filament through it at the high standard print speed ( like 120mm/s on 0.1mm height) you should convince lot of pro user… ; -)I also notice a big difference when extruder motor are setup to low or standard accel/jerk and that's worst with geared extruder. Mine are higher than movement.
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Prusa has a great acceleration calculator here:
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Hi all,
Where do I find the time?!?!
I have run a Volcano with a 1.2 nozzle, and that one works. I think I went up to 80 mm/sec just to see it print, but have not done any real performance testing on speed with the Volcano.
Speed seems to be tricky to measure anyway.I had upped the max speed, so that was not the factor. It simply was the acceleration. I am now printing visibly faster. Also, the printer is starting to shake a little.
Still have not figured out how to measure accurate nozzle speed. Maybe a ruler behind it, and shoot a video then calculate the speed by examining the frames. Phew, no time.
@W3DRK, no problem. There is a thread here somewhere, but I can answer here.
Yes there is flex in the drive cable, it is minimal as we stay well within the torque limits. But the flex goes into the gear system and is reduced 30:1. So it is reduced a great deal, so much so that it is not a factor. I use 1.2 mm retraction on my Delta and Brian uses 0.9 on his. So you can see it is minimal. -
Hi all,
Still have not figured out how to measure accurate nozzle speed. Maybe a ruler behind it, and shoot a video then calculate the speed by examining the frames. Phew, no time.
It's difficult to do. On a simple left to right move, starting from rest, there is a very quick "jerk", then it accelerates up the speed, maintains that for a while (assuming that the move was long enough for it to have reached maximum speed), then it decelerates down to a stop, changes direction and starts over. Do you take the bit in the middle as being he nozzle speed, or do you take an average of the entire move? Which figure is more meaningful?
IMO, it's all a bit academic as most machines are limited by how quickly the filament can be melted. I went to great pains in selecting motors that would give me the highest torque and acceleration but in practice, I can't anywhere close to using those numbers. Even non-print moves are set well below what is theoretically possible for the motors taking in to account the weight of the axes because it's just too scary. According to the calcs, I should be able to accelerate the X axis at a tad over 3,000 mm/sec/sec up to around 780mm/sec. In practice, I use about a quarter of the acceleration and half the maximum speed - it's far less scary.
Just my twopence worth.
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Lykle a more realistic real world test could be printing something and seeing how long it takes?
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Just feed filament as fast as the motor can push it, at temp… you can calculate the volumetric rate of extrusion, and therefore the maximum possible feedrate at a given layer height/extrusion width.
You can also calculate how fast the nozzle will be moving at any point in time using calculus (I believe -- I'm no mathematician) and plugging in the known values from firmware and the gcode file.
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I havent found that its possible to actually print anything near those speeds..
are people printing good quality at 300mm/sec??
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I havent found that its possible to actually print anything near those speeds..
are people printing good quality at 300mm/sec??
I doubt it. Most machines are limited by how fast the hot end can melt the filament and that is largely due to the size of the melt chamber and how long the filament stays in it, and also to some extent how hot you run it at. Some people push the temperature up in order to achieve higher speeds but that can lead to all sorts of other problems. Even if the hot end is capable of melting filament that fast, 300 mm/sec may be possible for longish moves but imagine infilling something that is only 10mm wide. For one thing, you have to accelerate, move, decelerate stop and change direction and repeat so you'd be unlikely to ever get up to 300mm/sec on such short moves. Even if you had instantaneous speed changes doing that 10mm zigzag will mean moving the the hot end back and forth 30 times a second. Even if that was possible without the machine shaking itself to bits, and even if the extruder was capable of such fast moves, the filament won't be - it's too "spongy" to be stopped and started that quickly.
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Your best bet for hitting printing speed limits is a largish smooth object printed in spiral vase mode - there are no corners or stops anywhere, so as long as the radius of curvature isn't too tight the printer can get up to its maximum speed and stay there.
For my printer I get fairly reasonable non-printing motion up to 300 mm/s, but print moves are limited by how fast the extruder can extrude. Currently my extruder is tuned to quite conservative settings (in terms of maximum speed, acceleration, and jerk) because I had some trouble. Maximum speed you can tune by simply extruding into air and seeing when you start skipping steps; of course this will depend on filament type and temperature. Acceleration and jerk settings for the extruder I find a bit more mysterious, but they're probably more relevant to retraction than to printing. Since it's your extruder you're testing, this makes sense; if you've got a good mechanical system, your print speed is limited by how fast your extruder can push your filament through your hot end.
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Lykle, what speeds did you hit with the volcano in the end? When did it start skipping/underextruding?
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I found on my corexy with 0.8mm nozzle with a volcano hotend, it stopped extruding over 50mm/s on infill.
