Sumpod – Jamming – resolution after extensive investigation

Spent yesterday morning trying to get the 3D printer working again following the recent upgrades (SD card reader, Encoder, new LCD with contrast control, second extruder, 3mm instead of 1.75mm filament and a keypad). However there is an age old adage "that if it ain't broke, don't fix it!" and that came home to me when I tried my first print after the rebuild.

On the Sumpod forum there has been a thread regarding some filament jamming issues and it has covered many items trying to find out what is causing it. Never having suffered jamming it was of general interest to me but came more into focus as soon as mine jammed. I had all the same signs, extruder jumping, printing stopping after a while and no obvious signs.

I decided that to find the reason for my jamming I would need to breakdown the system into 4 or 5 elements and then exclude each in turn. It must be remembered, and I wrote it down in big letters "It all worked before!" the elements I decided on were :

1       Extruder system - stepper motor, pressure nylon bush, tensioner

2       Delivery tube to push fitting

3       Hot end

4       Filament

5       Software

Because I did not want any problems when starting to print again I used the same set up. The extruder system was the same as was the hot end but I had to replace the tubing. When I took apart the hot end I discovered that the tubing seemed to have swelled. As I am working on a new hot end I thought I would change over to that so I could then eliminate the hot end if it still jammed, and it did in a spectacular way (see picture 3). There is still work to be done on the new hot end but it did provide the breakthrough.

Because the tubing had deformed so much I had to question the tubing. It was the only thing that was new and I should have picked up on that sooner but I didn't however, I now had a possible answer. I rechecked the supplier and description and found I had not been miss sold the tubing. It stated clearly that it was nylon but I focused  on the dimensions and not that I needed PTFE. Daft I know but that's what happened.

I now had a possible answer but how to prove it as the previous tubing would not be long enough. I the end I cut a piece to the length of the nozzle up to the base of the push fitting and hoped that the Nylon tubing could be held by the push fitting and as long as I could feed the filament past the joint by hand it should work as a temporary fix. Well it did and after the first print without jamming I decided on another item which failed! As I dismantled the hot end and saw a plug of filament in the nozzle. I must admit I was very disappointed because I thought I had cured the problem but this time it was slightly different because the filament disappeared! The extruder had decided to run backwards! I didn't even notice the filament had moved until the dismantle and then looked to see the filament was half way back to the stepper motor. Now that's strange because I had over 40 hours printing without problem.

I took the top panel off and using Repsnapper I ran the stepper motor only to find it oscillated. I adjusted the potentiometer until it ran correctly then reassembled the back end. Its not until writing this that I remember that  I fitted a second stepper driver for the dual system as well as more jumpers. Did I put the new driver in the old slot? I suspect I did.  Now with it all back I thought a really long print would be worth doing to test the system. So I designed an item to print that would test any jamming and nearly 4 hours later it was finished with out a hitch.

So the answer to my jamming was I had inadvertently used nylon instead of PTFE. A simple find in retrospect but aren't they always?

When the ordered PTFE replacement arrives I will replace the temporary fix and hopefully that will be an end to it......oh ......I still have to fully convert to Marlin don't I...

Come back and see how I get on.