Mendel90 connected to Octopi
December 28, 2016 06:05AM
Hi all,

I am struggling to get my Mendel90 connected to Octopi. Every time I am trying to connect, it tells me "communication error" --> so far I have been browsing the web under Octopi and also Thomas S. tutorial, but this part seems to be left out of the tutorial.
How do I load the MELZI HW information into the Octopi Image? Maybe this is the problem, as I did nto yet manage to get this done.
Thanks for any help.BR, Harald
Re: Mendel90 connected to Octopi
December 28, 2016 09:07AM
> How do I load the MELZI HW information into the Octopi Image?

Octoprint doesn't need to know it is a Melzi. All you need to do is select the correct serial port and set the baud rate to 250000. The port should be /dev/ttyUSB0.

Edited 1 time(s). Last edit at 12/28/2016 09:07AM by nophead.

Re: Mendel90 connected to Octopi
December 28, 2016 09:17AM
Thanks Chris.

Working now. I had to restart Octoprint and also realized, that the Jumperbridge was still closed on the MELZI. After removing this and doing another restart, it has now successfully connected. Yipppiie. Thanks again for the quick response.

BR, Harald
Re: Mendel90 connected to Octopi
December 29, 2016 10:19AM
Hi again,

printing is working now via Octoprint.
What is not working though, is the fan being switched on after layer 1 has been printed.
So far I have not found any setting in Octoprint that would let me configure it.
I have sliced the print with SKEINFORGE and printed it some months ago via Pronterface. I do believe that the fan was running at that time.

Does anybody have any information for me?

BR Harald
Re: Mendel90 connected to Octopi
December 30, 2016 04:26AM
The fan on command (M106 S255) should be in your gcode. It doesn't make any difference if the gcode is sent via OctoPrint or via Pronterface. Neither make changes to it, they just send it verbatim.

You can test the fan with the controls in OctoPrint to make sure it is working.

You can check the gcode by searching for the Z value of the second layer. There should be an M106 at the layer change.

Re: Mendel90 connected to Octopi
January 02, 2017 03:23PM
Hi Chris,

thanks again for your help and a happy new year to you.
The FAN can be switched on and off via the Octoprint button --> this test is o.k.

then I have checked the G-Code but could not find any M106 command in the whole G-code.
I have checked other files and could find it at the start of the second layer (Z=0.4). Thus it seems to be a problem of the slicing and I will re-slice and check the G-code again.

Now I am having a problem with my hot end (MK V). Last week the last print started off badly, but I did not recognize until an hour later. The PLA seemed to get stuck in the nozzle and "hardened/glassened?".
I then tried to remove the filament, cleaned the hobbed bolt and hoped to be able to feed the filament again.
No luck and after 3 tries, I started to disassemble the extruder head in order to get a better look at the hot end. In parallel I checked your blog about removing particles and tried that again - no luck. I could not feed the filament anylonger into the hot end.
So, I removed the hollow lock set screw and found the red insert (which I mistakenly considered to be the filament (as I used red filament at that time). Then I took a 3mm drill and started to drill out the filament, hoping to be able to remove whatever was the culprit.
Whem removing the leftovers, I realized that the red tube was not the filament but some kind of tube which "guided" the filament to the nozzle?
As the drill did not destroy the complete tube (only 1 3rd), I put everything back and re-assembled the hot end again.
When reloading the hot end with pink filament, it seems that the transport is not working well.

thus my question - can you help me to get a new hot end? Are you still selling those ones as spart parts?

BR from Germany,
Re: Mendel90 connected to Octopi
January 03, 2017 03:30AM
We have run out of hot ends but you can buy them direct from our supplier here: []

In addition, to build it up to the same standard we supplied you will need these parts: [], which we can still supply, and also some Carplan fire putty: []

Note that the thermistor supplied by is different to the one we used and needs a different table in the firmware. The one we used is available here: []

The bit that you damaged is the PTFE liner and that is available separately here: []. Because all the plastics we extrude are harder than PTFE a drill will always tend to wander sideways and damage it, so drilling it is a bad idea.

Re: Mendel90 connected to Octopi
January 04, 2017 03:05PM
Hi Chris,

thanks for the detailed information.
Do you think that replacing the liner itself could solve the problem? Although something seems to be blocking closer to the nozzle head. Everytime I load the filament, it extrudes for the first few millimeter, and then it gets stuck somewhere. Removing the filament is possible, but the culprits seem to be stuck in the nozzle head. So far, no luck of getting a print going again.

Regarding the hot end replacement - to be honest, I am a bit lost. I thought the ordering a new hotend would solve the problem, but once I read your sentence "Note that the thermistor supplied by is different to the one we used and needs a different table in the firmware" - I do not really know what I should do next. Sorry - I am not really that deep into programming that I would know what to do.

Regarding the parts that I would need on top of the hotend:
1 110mm x 25mm self amalgamating silicone tape
2 PTFE sleeving OD 1.2mm ID 0.71mm x 62mm
2 Heatshrink sleeving ID 1.6mm x 15mm
2 PTFE sleeving OD 2.6mm ID 2mm x 45mm
1 Heatshrink sleeving ID 6.4mm x 60mm
2 Red PTFE wire 16/0.2 length 170mm
1 Ziptie 100mm min length

Yes please can I order them via you? Can you let me know how much I should transfer (Paypal?). Would you also be able to give some instructions on how to utilize those parts?

Regarding the fire putty - charges about 18 pound for the shipment. I did find something similar in Germany via Amazon: [] - could this be the same? Where do you put this paste? Is that the red sealing around the nozzle head? I thought this would have been a rubber tube of some sort.

Will wait for your answer before ordering the new hot end. I am still not sure if I will manage to assemble everything correctly and to also get the firmware updated. Would appreciate your help a lot.

BR, Harald
Re: Mendel90 connected to Octopi
January 05, 2017 01:51PM
A damaged PTFE liner will definitely make it harder to extrude and can stop it completely. If you drilled the top out to a bigger diameter then PLA will expand to that size and then be hard to squeeze into the smaller end. If you made the hole bigger all the way down then you will get more backflow and that creates more friction. If you shortened it then it won't clamp tight at the bottom and form a seal. If you made the inside rough it will also make it hard for the rubbery PLA to slide down it.

I can't guarantee replacing it will work but there isn't much to go wrong with the brass part other than something blocking the nozzle. To fix that you need to push something up the nozzle 0.4mm or less diameter. I used a 0.4mm drill but I have seen acupuncture and hypodermic needles recommended. With a drill you have to be careful not to make the aperture bigger as brass is quite soft.

To change the thermistor setting you need to edit configuration.h and change it to the Semitek one and then recompile and download the firmware. They are less accurate than the ones we supplied. I needed them to be 1% so everybody could print with first print with the same gcode.

We can supply those parts for £2 plus 20% VAT plus £1.52 postage = £3.92. Yes you can pay by paypal. PM if you don't know the address.

The fire putty is used to cement in the resistor and the thermistor. It sets to a biscuit type strength until you heat it for the first time and then it sets rock hard and will handle thousands of Centigrade. I can't tell if the German amazon product is the same stuff.

Assembly is not straight forward, which is why I pre-assembled them all for the kits. I cured the cement with a 7V bench supply before soldering the wires on and bending them as the cement is too fragile and you don't want to connect the thermistor when it is wet.

I can buy one from and prepare it for you but it will be expensive and take several weeks to import one from the USA because I will be on holiday by the time it would arrive.

Re: Mendel90 connected to Octopi
January 09, 2017 03:44PM
Hi Chris,

the hint about the acupuncture needle is great. I might be able to try this out.

I guess that I misunderstood the part about the thermistor. When going for the one from, I assume that there is no need to recompile anything, right?

Regarding assembly: I'd like to take your offer. And I can also wait. But I might have found a solution to the long shipment time. When browsing Oozenest, I found that they are also offering the J-HEAD MK V-BV HOT-END, and even the price is lower (30 British Pound). Would that not be a possibility? Then you do not need to buy one from

Please PM to let me know the price and the paypal address.

thanks so much,

BR, Harald

Edited 1 time(s). Last edit at 01/13/2017 12:29PM by nophead.
Re: Mendel90 connected to Octopi
January 13, 2017 11:55AM
Yes Oozenest stock the 1% thermistor I used, so no firmware changes needed.

I didn't realise they also stock the genuine J-Head, so yes I can get one from there for you?

Edited 1 time(s). Last edit at 01/13/2017 11:57AM by nophead.

Re: Mendel90 connected to Octopi
January 13, 2017 11:56AM
Ah, but they only stock 0.5mm, is that OK for you? We shipped 0.4mm.

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