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Help required with MK7 head used on Prusa i3, I have been printing for one night now (last night) with very pleasing results for my first night of printing with over 11 items, however when I printed the 12th, a replica of the 11th the head blocked (I think) and it just wouldn’t extrude correctly – jamming up. I dismantled the head then gave up (early hours of the morning).

Today I took the parts to my works workshop cleaned out all of the parts re-assembled and at temp (195˚C could extrude again however the extruder motor jumped (if that’s the correct term) kinda made a clicking sound and kickback of the PLA. Before going to print it would extrude however now and again I could hear a clicking sound, but will now no longer print / extrude when printing.

I have tried many times to print and many rebuilds of the head, getting late now so I have ordered new heads and the M6 part along with some PTFE tubing. But why did it work and now dead extrusion?

If anyone can help out it would be most appreciated.

Info just in case you want my set up:

Prusa i3 from Folger Tech (USA)

MK7 head – 1.75mm

I was using 1.75mm PLA

RAMPS 1.4 on Mega 2560

I was extruding 300mm/min with 5mm extrude, no problems (pronterface)

Slic3r to produce G-Code – all standard settings (60mm/s with all other prints) – tried 30mm/s and also increased and decreased the temperature with no luck (185 – 220)

Pronterface to talk to the printer

Set all corners Z to home on the glass

Using really strong hair spray on the glass (bugger to clean but it appears to have worked)

3 of the first prints were medium (50mmsq) but the remaining prints were not that big and the final was a copy of the previous (but just stopped extruding)

The Head temperature only dropped by about 40 ˚C between prints (previous prints dropped more and re-started a new print, fine) a couple were totally off before restarting.

Now I cannot print

Can anyone let me know where I have gone wrong?

Thanks in advance

Me

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Hi Neil.

Sounds like the extrusion stepper motor is stalling. That’s usually because it’s working too hard. If it’s stalling with a clear nozzle you may have reassembled the extruder wrong. If it’s stalling when you’re attempting to do a print, it may be that the nozzle is too close to the build plate and there’s too much backpressure so you need to reset the bed height.

Course, it might be that the extruder wheel is simply not getting enough purchase on the filament and/or the teeth could be clogged. That causes a clicking noise on my printer. Usually if I carefully clean the wheel thats’ enough to get her going again. Main causes of this are usually either that the spool is dragging or heat is getting up above the wheel and softening the filament - PLA softens at a relatively low temperature.

Let me know if any of this helps. Afraid I’m not familiar with your setup so my comments are all general but hopefully something will help you.

Cheers!

Andy

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Andy, thank you so much for taking the time to help me out, as per your suggestions:

The printer I have built: http://folger-technologies-llc.myshopify.com/collections/frontpage/products/folger-tech-reprap-prusa-i3-clear-frame-full-3d-printer-kit-ramps-gt2

The motor is not stalling, I don’t think, more jumping / jittering if I feel or hold the filament just before it enters the head it kind jumps a bit forward and then jumps back, but not all the time and only when the filament is extruding, i.e. some will extrude and then a bit will stall. Initially I thought the motor shaft was bent, causing a bit of separation between the gear and the idler pulley, but I have inspected it by eye and it still appears to be concentric, possibly the best thing now is to use a DTI to check the concentricity of the shaft, I did try to send a move to the control to spin the motor but it will not move unless heated. So I need to figure out how to ignore the cold prevention part of the code. Otherwise swap the motor for one of the others.

After the initial jam the gear did have molten parts of PLA in between the teeth, but I have since cleared this out, unclogged the main M6 shaft, cleaned the PTFE tube, and cleaned the build up inside the nozzle. I also tried using the head without the PTFE tube but that didn’t work either.

I have always reset the beds Z depth to 0 in all four corners, after disassembling the head.

One thing I have noticed, and only after this event is that the motor is very hot, too hot to touch, but saying that the X axis motor gets very hot also, noticed that one before the event, and have monitored with an external probe.

The only thing I can conclude is either the motor shaft is no longer concentric, the nozzle was FUBARed and no matter how I cleaned it, it was a losing battle or the heat soak has been getting up the tube due to incorrect reassembly.

I am a bit stuck now waiting for parts, I have accidently pushed the drill (by hand) through the nozzle thinking it was still a bit burred (this was the brass) and now I have a 2mm nozzle not 0.4mm

And the PTFE tube has been cleared out so many times it has seen better days.

I have searched the net for assembly photos with no luck, so I might model the parts and assemble them in Inventor to try to see what I have done wrong.

Thanks again Andy, if you or anyone else has any more suggestions please please post up.

Happy New Year All

Neil