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Extruder backlash with ParCan hotend attached

Posted by w0301 
Extruder backlash with ParCan hotend attached
August 17, 2012 07:03AM
I have problem with my extruder. When it is extruding there is something like a backlash on wade's big gear (see the video). I am extruding PLA at temperature of 190 C. When I higher the temperature and lower speed backlash does not occure so often. I guess problem might be that PTFE tubing does not fit very well on nozzle but if so how I am suppose to attache it better. Or maybe a crooked PTFE tubing can also be a problem? I have this problem for a long time, I can print at lower speed and at high temperature quite well but I want to get rid of it. So if you have any ideas how to solve this problem please share. I am also attaching photos of assembled/unassembled hotend.
open | download - IMG_20120817_120639.jpg (553.7 KB)
open | download - IMG_20120817_122953.jpg (567.4 KB)
open | download - IMG_20120817_123009.jpg (602.2 KB)
Re: Extruder backlash with ParCan hotend attached
August 17, 2012 07:29AM
Backlash is an aspect of the distance between the teeths, the aspect which gives a small stop of the driven gear when the drive gear changes direction. If there is no change of direction then backlash cannot be evidenced.

So that video is about your gears slipping, but has nothing to do with backlash.

Ideeas or fishing points:
- increase stepper driver current by adjusting the pot
- increase the springs pressure on the filament
- clean the hobbed bolt of pieces of filament
- ensure the top of the filament isnt too hot so it doesnt gets too soft

Edited 1 time(s). Last edit at 08/17/2012 07:30AM by NoobMan.
Re: Extruder backlash with ParCan hotend attached
August 17, 2012 07:57AM
Assuming that the teeth of your gears are always engaged this looks most likely to be a stepper current issue. It appears that your motor does not have enough current to push the filament through the hotend. As NoobMan suggested, try upping the stepper current and/or increase the extrusion temp (~195C-200C) to reduce the pressure needed to extrude. Definitely not a backlash issue though.
Re: Extruder backlash with ParCan hotend attached
August 17, 2012 08:11AM
Thanks for suggestions. Adjusting the pot to maximum, increasing spring tension and extruding at 210 C seems to solve the problem. I will try to print something to see if it is really ok.
Re: Extruder backlash with ParCan hotend attached
August 17, 2012 08:15AM
I have always been dubious about that hot end design. I think there will be a small shoulder where the end of the brass is inside the tube. PLA above its glass transition is like rubber so it will swell, and catch on the shoulder and be prevented moving forwards until it is melted. I think that will limit the speed.

You want the filament to slide into the barrel unimpeded (even when swollen) so that a large surface area is in contact with the metal to be melted quickly.

Try turning the gear by hand with the hot end at temperature but with the motor off. If you can turn it relatively easily then the hot end is OK and you need more motor torque. If it is hard to turn at a reasonable extrusion speed then the hot end is a fault.

Re: Extruder backlash with ParCan hotend attached
August 17, 2012 07:54PM
After little extruding my extruder jammed. It was almost impossible to extrude even on higher temperature. I thought that it was because hobbed bolt was destroying the filament too much (mushrooming is probably better term for this?) but the main reason for that was probably jam in the hotend that I found when I unassembled it (see the attached photo). PTFE tube is probably not fitting well on barrel. Maybe I shouldn't screw the barrel fully into the PEEK (I saw on few photos of ParCan hotend that it is not screwed entirely. Mine wasn't neither probably but I had to reassemble it because of filament leakage few days after I got it and I screwed it entirely). I will clean the nozzle and assemble it again without screwing barrel entirely. I hope that it will be ok.
open | download - IMG_20120818_013143.jpg (565.6 KB)
Re: Extruder backlash with ParCan hotend attached
August 18, 2012 11:29AM
I have cleaned the jam and assembled the hotend. I was able to print black PLA at 220 C (see photo). But last three solid layers didn't print well as you can see on photo. Jam again? I extruding seems to be good even it is at pretty high temperature. What could cause those bad 3 solid layers? I will look if there isn't other jam in hotend. In case there is do you have any ideas how to attach PTFE tube to brass so it is not detached during printing?
Re: Extruder backlash with ParCan hotend attached
August 20, 2012 02:36PM
Hi Guys.
I have been somewhat busy with real life stuff so have taken my eye off the ball here for a week.

I Designed My Mk 2 in November last year and realeased it in January after a fair bit of testing.
I am still using Production Nozzle no.1 8 months later with no issues.

W0301 : It almost pains me to see the abuse your nozzle has taken. All the corners rounded and the Tool Marks on the PEEK.
Your PTFE Tube is rather well knackered, In reality replacing that would more than likely solve the problem....

Please get back to me, alex at par (six four) dot com . replace (with numbers)
I'll replace your Nozzle Free of charge.



Edited 1 time(s). Last edit at 08/20/2012 02:43PM by Parcan.
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