mendel-parts gen9 extruder - finally got it working properly!

Hi Everyone,

I've just managed to get my mendel parts gen9 extruder printing properly after a few months of mainly mangled prints. I thought i'd share what I did in case it helps someone else. Its a bit drastic though!

The gen9 hotend is basically a couple of brass tubes with a peek block in the middle. Theres nothing complex about it and it fixs into an aluminium carriage with a single bolt. The problem i've always had is that after a while it was very hard to push the filament into the hotend. I nearly gave up with some faberdashery grey filament that was a bit soft. I saw somewhere that the issue was to do with the fiament swelling in the heating chamber and then jamming in the peek block, stopping more plastic from being pushed down. I've also seen warnings about taking the gen9 hotend apart as it needs redrilling. I bought a long 2mm drill and did it anyway and had loads of problems afterwards. Redrilling the hotend didn't do anything and I kept getting prints fail after a couple of layers.

To fix it, I changed the shape of the hotend slightly. I figured that the filament was getting jammed at the top of the heating chamber and may have been jammed inside the peek, which is only a couple of millimetres long. I saw a few people mention tapering peek blocks by drilling them really fast so the swelling caused the hole to be tapered and that this made them impossible to jam. The next best thing is a bigger diameter on the bottom section so I drilled out the bottom piece of brass to 2.5mm. There's a small internal lip at the bottom of that tube which I assume had a purpose so I used a 2mm drill to measure the distance, transferred the measurement to a 2.5mm drill using the drill chuck as an end stop and drilled out the inside. I also drilled out the peek block using a 2mm drill, but pushed it round the outside to open it up slightly (a 2.2mm drill would have been better). When I reassembled it I got lots of oozing on the first attempt but this was ta 250 degrees. Turning down the temperature worked and I can extrude at 195 but only slowly. I also don't need to tighten up the extruder springs as much which was destroying the soft grey filament.

I have a new x carriage printing and I'm hoping not to tempt fate by posting this before it finishes, but its looking promising. I had some issues with a shot glass having some stripes where the filament wasn't extruding. The stripes are periodic so I'm assuming its a problem with the pid control of the heater though so it looks like i can print again. I noticed that the filament I was using is 1.8mm diameter which might be too thick for a 2mm hole.

If there's any other hotends using similar designs i'd be interested in testing one as i've had lots of trouble so far with the mendel parts stuff.

Pete

I too had problems with the v9 design on my orca. I switched to a J-head from hotends.com and got the mounting bracket he sells, fits on the orca 0.3/0.4 (probably the older ones too) with just drilling a single hole, don't even need to take anything apart, took 5 minutes to mount.

I gave up and purchased BudaSchnozzle 1.1. Had to make new X carriage.

Vedran if the budaschnozzle comes in at 95$ and it needs a new x-carrige to be mounted the equally good and well tested design of the J-head that only costs 55$ + 10$ for the mounting plade seems like the better choice, considering it can be hacked on without any real mods

I spent most of last night watching a new x carriage print out with the occasional desparate rush to push the filament back in when the drive gear started slipping. Its the most success i've had so far and I have a new x carriage with only a few missing layers. I was printing a linear bearing carriage at 50mm/s and every so often it looked like the chamber was cooling down too much as it would pick up again eventually. I think the pid constants are not tuned for my setup in the mendel parts download of marlin and its oscillating a lot (assumed because I sometimes get regular stripes of blobby extrusion). I've replaced quite a lot of my orca now and need to upgrade the z axis as its not completely level as well as the y axis as its making a racket and the bolts keep coming loose.

I ordered a makerbot stainless drive gear as another upgrade as the brass gear is slipping a lot on the soft grey filament i'm using. Hopefully the excessive grip will give me enough leeway to keep the temperature lower and focus on tuning the pid controller. At the moment as soon as it slips I have to jump in to save the print which means continuously watching the printer.

The mendel-parts gen10 extruder looks to be the same design so i'm guessing it would have the same issues.

Pete

I hat problems with this hotend too. In my Orca the gap between the brass insert/idler and the opening of the hot end is too big, the filament bends away to the side after a short time.

I fixed it with this part on thingiverse, I don't have problems with the extruder any more. Maybe this will work for you too?

I added that part on at the weekend but I still had problems. It stopped the filament looping out but it didn't stop the drive gear from eating into the side. I also added a box over the fan with a hole to direct the airflow directly onto the drive gear (not a very good design, its just a box with a hole) as I thought the stepper might have been heating up and then softening the pla. That didn't help, neither did turning down the stepper motor to just above where it keeps stalling. I think its the soft pla but the extruder should be able to cope. I think drilling out the extruder made the most impact and the remaining issue is to do with the pid control and possible bad heat transfer in the hotend giving the wrong reading on the thermistor. the hotend temperature reading hardly changes but its the only thing I can think of that will be causing it to stop extruding.
Pete

I've been running a v9 for a long time, and agree that they can be a bit temperamental, but it is possible to get good results. It sound like you are using 1.75mm filament, so there is less strength in the filament to push through what is quite a long hot end. I have a 3mm version with a 0.5mm nozzle. I found the worst thing to do was to leave the hot end at full temperature and not printing: heat travels up the hot end and filament eventually melts and sticks to the PEEK. I had much more success once I had run a 3.2mm drill down through the assembled hot end (it is drilled out to 3.2mm anyway) which removed a slight lip on the PEEK, making the channel smooth.

Cooling the top of the hot end with a fan really helps. I have an aluminium heatsink attached to the top of the hot end too. To keep the heat in the hot end and make it more consistent, make sure your heater block has some fibreglass insulation over it, especially if you have a fan as well.

PID temperature control helps massively, make sure you tune it with M303 to get the constants you need, then put these in your firmware. My temps stay within +/- 0.1C of target temperature. However, you need to have a good thermistor connection: if your temperature is fluctuating, check/redo the thermistor connections. This may also depend on your electronics, as older Gen6 electronics is prone to a fluctuating 5V rail, which messes up the thermistor readings.

It also may be worth you increasing the temperature you extrude at, by 5C. It should make the filament slightly more liquid, and make extrusion just a little easier.

Thanks Droftarts, I'm already extruding at 240 degrees but insulating the brass block really helped and i've managed to get some full prints out at last! I wrapped a few layers of wide kapton tape around and made sure it didnt lay too flat so theres plenty of air trapped in the layers. Its pretty good now and i'll try reducing the temperature once i've got a few things I need printed out. Next problem is levelling the y axis. I printed a tall object and its shifted towards the back along the y axis. I'm assuming the bars aren't perpendicular so i'm printing some linear bearing mounts instead of trying to adjust it using the ball bearings in slots.
Widening the bottom of the extruder has definitely helped but it oozes more now. I'm happier with a bit of ooze then failed prints though.
Pete