Success stories with direct drive and standard Mendel extruder piece?

Hi,

So I've completed my Mendel, and I've extruded by hand, but I haven't been able to extrude via stepper motor yet.

I'm using the standard Mendel extruder piece with a Mercury motor SM-42BYG011-25 that I got from sparkfun (which according to this page has 23 N-cm of holding torque.

I was originally planning to use a gear wheel on the shaft, but when I went to mount the extruder stepper motor on the Mendel extruder piece, I saw that it wouldn't fit.

I then cut splines in the shaft of that stepper motor, and mounted it. I'm having no luck getting the stepper motor to grip, push down the plastic, and extrude.

Either I mount it too close to the bearing and I can't push anything in, or I mount it somewhere in between and the motor stops turning, struggling to push down the plastic, or I mount it too far out, and the stepper slips completely (and I can push the plastic in by hand).

Has anyone else had luck with the standard Mendel extruder piece? What did you do for grip?

Because I no longer have the Makerbot that I was using as a RepStrap, I can't print a geared extruder until I get this one working.

Any ideas? I'm fine buying a new stepper motor with higher torque, and even cutting splines in its shaft if I have to. Anything I can do to get the existing Mendel extruder piece (which is now J-B welded to a perfectly good PTFE insulator) to be part of a working extruder, I'm up for.

I've been trying to extrude PLA (well, I DID extrude PLA, by hand), and the PLA isn't even getting notches cut into it like the plastruder does on the Makerbot.. I even tried ABS, but still no luck. The stepper motor seems too weak.

Help!

Thanks

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--Jeff Keegan (Just Another RepRap blog)

Try turning the stepper current up until the motor starts to overheat, then turn it back just a bit. If your extruder is PLA, make sure you don't melt it.

Then run it as slow as possible, about 4 mm/s.

Finally, if it still won't work, you can try drilling out the nozzle; 0.5 mm is probably the smallest you want to start with, larger will be easier.

Then print a geared extruder.

I had exactly the same problems as you, and I was only able to get the standard extruder to extrude very slowly.

Wade

Thanks I'll try. I'm using Extruder Controller 2.2 though (gen 3 electronics). Is there a current adjustment on that board? I remember reading (and just reread now) that the trimpot on the board is currently "unused". But I'll certainly play with the extrude speed.

Which firmware were you using? I'm using FiveD and get that horrible whine from the motor.

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--Jeff Keegan (Just Another RepRap blog)

The FiveD firmware uses the trimpot to set the value of the current through the PWM chips on the extruder board. (it can be done through G-Code as well but the RepRapHost software assumes the trimpot by default.

Please note that if you put too much current through the stepper motor it does not respond correctly either. The whine from the motor will always happen (It has been discussed in a different topic), as the PWM chips cause a vibration in the audio range. Reading the messages, it seems that this whine goes aware if a true stepper driver is used (and it gets even quieter if you can use micro stepping).

Dave

The whine is from the PWM frequency, by default it's about 1 kHz. You can increase it if you want, but it works fine for me. I use an extruder controller board as well, with the PWM set to 0.75, but that will depend on your stepper. I'm also using some pretty strong steppers - 5 kg*cm, and a geared extruder.

With the current set correctly, you should be able to extrude slowly at first with the standard extruder.

Wade

Ok, so I've modified the firmware for the new 20100719 build to accomodate my McMaster pulleys and my extruder particulars.

I set X_STEPS_PER_MM to 7.8693, Y_STEPS_PER_MM to 7.8693, Z_STEPS_PER_MM to 565.1491 (which seems strange that it's higher than the 320 it was by default.. is the Z axis full stepped or something, changing the 400 in my calculations to 200?).

I changed E_STEPS_PER_MM to 0.706 based on the Commissioning page, as well as setting E0_STEPS_PER_MM to the same just in case E_STEPS_PER_MM is now outdated(?).

I also defined USE_THERMISTOR, which surprisingly is off in the standard Mendel configuration..

What I CAN'T figure out is exactly how to change my extrusion speed to be around 4mm/s (240 mm/min). If I look at the Extruder tab on the Preferences dialog in the RepRap Host software, I see a few things that look like they might relate to extruder speed:

Extruder0_ExtrusionSpeed(mm/minute) - defaults to 3000
Extruder0_FastEFeedrate(mm/minute) - defaults to 18000
Extruder0_FastXYFeedrate(mm/minute) - defaults to 3000
Extruder0_MaxSpeed(0..255) - defaults to 255
Extruder0_SeparationSpeed(mm/minute) - defaults to 3000
Extruder0_SlowXYFeedrate(mm/minute) - defaults to 1500

Yes I've just read through their descriptions at
[reprap.org]
so I can take a guess that I want to leave MaxSpeed at 255 and lower the rest to around 240 (or whatever speed I can actually extrude at, faster if the motor stalls), and that's what I'll try next time I'm at my machine, but if someone who's been down that road knows the answer, I'd appreciate the hint..

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--Jeff Keegan (Just Another RepRap blog)

It looks like 672 was my magic Z_STEPS_PER_MM value, which I found by trial and error. I put a piece of tape on the side of the hex nut on the leadscrew that was facing me, and I did 10mm moves up, one after another. Since the M8 threaded rod I have has a 1.25mm pitch, The tape should go around 8 times every 10mm. (again, I have a McMaster pulley in there, not the standard Mendel pulley).

While I have the machine powered up I'll try lowering all of the speeds and just have it extrude for a while (although I'm not sure I trust the Extruder tab.. It says "Extrude speed" (defaulting to 3000 mm/min), when that's clearly acting as an extrude duration, not a speed. Maybe it's different when printing. Maybe the speed preferences only affect gcode generation?

I just came to a realization about my bed.. (I'd seen that the extruder nozzle was higher off of the bed on the right side of the bed).. I blanked out and missed the super obvious answer.. I thought that the spacing I'd done wasn't perfect, and I needed to adjust that side of the bed (but deep down I knew that couldn't be right). Nope - last time I took my z-belt off, I must have had the X-axis slightly off.. I need to turn the right hand leadscrew about a turn or so down.. I really don't want to loosen that z-axis tensioner - I finally have the Z axis working somewhat reliably. Agh.. But I digress. Sorry for babbling - it's.. AGH - it's 5am! Jeff sleep now.

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--Jeff Keegan (Just Another RepRap blog)

Hey Wade,

Does this Kysan stepper motor have a round shaft or a D-shaped flat-cut shaft?

[store.kysanelectronics.com]

Trying to find a high torque round (or knurled if I could find it, but I'm not holding my breath) shaft motor to cut splines into, so I can make my existing extruder piece work before building your geared extruder.

(I've been able to extrude slowly, but not in a way that will yield an actual print.. If I tighten up the motor so it can get a more consistent grip, then it often stalls. I even tried switching to full steps instead of half steps, which seemed to help, but not enough).

I've been through the list at [reprap.org] and other sites (tried Anaheim Automation but their steppers all have D shafts).

Actually maybe I'll buy the Lin Engineering - 4218L-01-10.. My concern was that with the smaller shaft the splines might come out differently, but maybe that'll be better, and it's only $10. Either way, I'm still interested in your answer.

Thanks,
..Jeff

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--Jeff Keegan (Just Another RepRap blog)

Ah, looks like it's 5mm round (the Kysan one). Sadly they have a $100 limit on their store. Lin it is!

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--Jeff Keegan (Just Another RepRap blog)