I got the following very valuable information from Velleman support (thanks Yves!) that I think should be part of the assembling instructions:
The hot end screw should be tightened with 3,5 Nm - that is the recommended torque!
Since I did not have a torque wrench myself, I brought out the old physics formula collection and did some torque math. I ended up with a perfectly tightened hot end - no leakage at all and no ruined print head this time (I did ruin it the first time around…).
Just wanted to post this for all you that are building your K8200s - I got this as part of an email and have not found it elsewhere.
I’ve just started building the printer, and I started with the extruder assembly as this seemed the most difficult bit.
I’ve assembled it, and I’m not sure if it’s tight enough or not.
I don’t have a torque wrench either. Can you explain how you estimated the torque you applied, please?
Short of putting the bolt in a bench vice and hanging 0.35 kg on the end of a 1 metre spanner (or 0.7 kg on the end of a 0.5 m spanner, etc.) any slightly more practical suggestions would be appreciated!
I observed that the black washer was not flat before I fitted it, so I judged the tightness by tightening the assembly until the washer was almost flat.
And was that right? tightening it until it was flat? I also don’t have a torque wrench, and I thing that 3,5 Nm is not enough force to make that black washer flat.
I have now completed building the printer… and it works!
It definitely doesn’t leak and I don’t appear to have done any damage - at least the nozzle has stayed attached. I haven’t tried to undo it to check the threads.
I probably should have said in my previous post ‘tightening the assembly until the washer was almost flat’. I will update it…
I think the actual seal is the metal-to-metal contact between the nozzle and the metal cylinder it screws on to. So how flat the washer is may be irrelevant. Therefore the recommended torque is probably correct.
Had that the first time. The second time I got it right; washer was NOT flush, but it didnt leak (at least not with PLA). Then I tried printing ABS, had some burned PLA blocking the extruder and had to clean and remount a third time, and then I snapped it, again before getting the washer flush. Despite what some say, its not a good indicator. A torque wrench is pretty much a must, too bad velleman provided the torque when it was too late for me :(.
BTW, I really hope Velleman consider switching to a different hot end design for “version 2.0”. We’ve ordered this hot end: e3d-online.com/E3D-HotEnds/E3D-D … tal-HotEnd but we will need to improvise something to mount it. And I cant print a mount meh
The nozzle should NOT be tightened until the washer is flat!
The only reason for the undulated washer is to hold the heater block in place. Tighten the nozzle with a torque wrench to 3.5 Nm and do not look at the washer.
I purchased a torque wrench specifically for assembly, and I snapped my barrel Have filled in a missing parts request for another - hope that is ok. It has snapped clean off at the point where the screw threads start to be cut into it.
I had set the torque wrench to 2 Nm and tightened it fine till the wrench indicated it was there. I then set it to 3 Nm and tightened it fine until the wrench indicated it was there, and then I set the wrench to 3.5 Nm and very gently applied the turning force and the barrel snapped before the wrench indicated I had reached 3.5 Nm.
So now my inclination when the replacement arrives is to only do it up to 3 Nm - is this a bad idea? Do you think it was a dodge nozzle, or a dodge wrench (it is brand new, and came with a hand singed calibration certificate dated 6 Jan 2013, so it shouldn’t be that bad).
Also I am wondering about completing construction but putting the connections to the hot end though a plug block, so that when my new nozzle arrives I will be able to unplug the hot end without needing to be soldering/unsoldering.
My thought: switch to another hotend. The E3D is working very well for me, and its so easy to remove the nozzle and clean it, then remount it. Suggested procedure for the E3D is heating up the block to 300C then hand tighten it. Works a treat, no leaks, no snapping. Only problem is that you need to print or improvise a mount for it.
I decided to make the connections between the ribbon cable and the heater and thermistor with a 5A terminal block (where the connections are made with screw terminals), rather than soldering. This has worked fine.
I have made the connections to the heater and NTC using a 5A terminal block as suggested by timp32.
My replacement barrel has arrived this morning (excellent service from Velleman, thank you).
This afternoon I will very gingerly try and tighten it all up again …
Must say despite this set back I am really enjoying this kit, and am impressed with the community that surrounds it. P4man - I will certainly consider other hot ends in the future, but for now I am committed to finishing this kit as per Velleman’s design.
I didn’t do it tight enough, and it startet to leak. .