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  1. #1
    I fitted my 3d pile of bits together today and mounted the head on my CNC table but the results were less than useful?

    I can't seem to get any material extruded, well practically none anyway.

    Its just slipping the feed rollers, even with a hefty push by hand on the filament while the motor is jogging produces nothing more than a tiny blip every minute or so, you can feel the motor trying to feed.

    I was expecting to see a thin thread extrude but not so.

    I have tried raising the hotend temperature all the way to 250c but no change really.

    The head is a 0.3mm one and i have uprated the motor as my drivers only go as low as 1.5A and the supplied motor was only 0.84A.

    I calibrated the A axis by removing the hot end and feeding filament then measuring it etc that seemed the right way to set it?

    I have speed in Mach3 set to 100 and acceleration to 20 i think.

    The code seems to run fine at least.

    Have i started out with a bad head or too small a nozzle for PLA??

    Any suggestions?

    This is the head BTW...
    Last edited by Davek0974; 25-02-2014 at 03:51 PM.

  2. #2
    Things that occur to me, in no particular order and with apologies if you've already checked...

    Is the hot end really at the temp it says? I'm not sure what PID controller you are using but there are various common thermistors in use and they are all calibrated differently. In the end I calibrated mine by taking out the filament and shoving the business end of a thermocouple down the filament hole so I was reading temp actually inside the nozzle.

    Looks like a direct drive from stepper to toothed drive roller (or whatever it uses) which does need a bit more urge on the stepper than a geared drive but if it's slipping, then there is enough drive but not enough grip (maybe). Can you release the pressure/grip on the filament and just shove it by hand? I'm more used to 3mm filament but you can get it to ooze through the hot end with firm hand pressure and I would expect your 1.75mm to do the same.

    I'm guessing that you have calibrated the extruder by telling Mach3 to push out a known length of filament, and checking that it has done so? Was that with the nozzle removed? Current versions of Slic3r expect this to be the length of filament going in; older (much older) versions used the length of extruded filament coming out which wasn't that easy to measure... I've no idea what values you would expect to see in Mach3 but acceleration on the extruder motor is a pretty meaningless quantity, I suspect, as the motor (especially with direct drive) hardly turns at any real speed.

    Can you measure the actual nozzle diameter (by sticking a bit of fine wire or drill up it)? It isn't blocked, maybe?

    Is the filament easy to push through with no roller pressure or nozzle? In other words, it's not oversize for the feed tube, etc?
    Last edited by Neale; 25-02-2014 at 05:28 PM.

  3. #3
    Hmm, the head was calibrated exactly as you describe, I took the hot end off and just fed filament and measured it.

    yes it's a direct drive via a small brass gear and pressure roller.

    i will try measuring the temperature tomorrow, I presumed it was not far off as at room temperature, the display was spot on, I'm using a Rex C100 pid controller.

    i have tried forcing feed by hand but could not get anything more than a smudge out. I will try withdrawing the filament and checking the hole.

    am I right in guessing I should get a continuous thread of PLA out?

  4. #4
    I have tried raising the hotend temperature all the way to 250c but no change really.
    250C is way to high for PLA at that temp it should just ooze out. As Neale has said is the thermistor calibrated you could check it with dipping the nozzle in boiling water and see if the temp is around 100C. If the thermistor is not quite touching the hot end that could be another problem.

    Going off memory the thermistor should measure about 100k at 20C but they are all different. One way to calibrate the amount going through is to mark the filament say every 10mm for about 200mm with a felt tip pen then instruct the soft ware to send say 30mm then you can work out if it is short or long. without the nozzle on, then when you get it near do it with the nozzle on.

    If you have the heat too high it will burn and block the nozzle. Just my two cents worth. ..Clive

  5. #5
    Thanks, this head has a K type thermocouple on it so no resistance to measure. I will try and check calibration tomorrow, I have a bare thermocouple thermometer somewhere, should be able to pass that down the head to the tip if I can get the filament out.

    the filament was feeding very nicely 100mm for an instruction of 100mm so it was set right but the feed just slips when head is fitted, there is no way it would feed as I couldn't even force it out by hand.

    i may have made it worse by overheating then so a clean out is in order I think. I'll warm it up and prick it through with some wire etc.

  6. #6
    I run PLA with a nozzle temp of around 190C although I tend to fine-tune this depending on the particular batch of filament I'm using. I don't have enormous faith in the exact temperature as I don't know how accurate my thermocouple is, but that's a reasonable starting point anyway. You should certainly get a continuous fine thread of filament coming out - anything else means poor print quality.
    Definitely a problem if you can't feed filament by hand, and it sounds like nozzle not hot enough or blocked - good luck with unblocking what's in there at the moment!
    I'm interested to see how you get on with the PID controller. I spent quite a lot of time tuning the parameters of mine (built into the Sprinter code) to get best warm-up time with minimum overshoot and best stabilisation. I have built a couple of hot ends with different heater power and now have two different sets of PID parameters (especially the P and I components) to get best results. I'm curious to know if the commercial PID controller has some kind of self-learning to achieve the same results.

  7. #7
    Yes the pid could be an issue, they tend to like more thermal mass, this thing heats up in about 45 seconds!

    it does have auto-tune and I've run it once, not had a. Chance to check the parameters yet.

    not sure how to unblock it yet, any suggestions?

  8. #8
    I've seen suggestions on how to clear overheated and blocked nozzles but can't remember details as I've never (luckily) had to do it myself. A bit of directed googling on the reprap forum site will probably turn up some ideas, though.

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  10. #9
    Quote Originally Posted by Davek0974 View Post
    Yes the pid could be an issue, they tend to like more thermal mass, this thing heats up in about 45 seconds!

    it does have auto-tune and I've run it once, not had a. Chance to check the parameters yet.

    not sure how to unblock it yet, any suggestions?
    Acetone will dissolve it ok, its also good for cleaning the bed the stuff you buy for finger nails etc quite often has a wax in it to make the nails shine so it is not good for the job.

    I have bought pure Acetone off the web in the past. I am surprised that the nozzle will heat up in 45 seconds. ..Clive

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  12. #10
    You can generally buy acetone anywhere that sells glass fibre supplies (yacht chandlers are good but only if you're near the coast!) as it's used as a cleaning solvent.

    Heating up time is a function of how much heat you can get into the hot end - my second attempt uses a couple of wirewound resistors as heating elements and draws around 4A - 48W of heat going into that small object heats it pretty quickly although mine might be nearer a minute to get to temp.

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