I have found that I need to use different temperature settings with the J-Head.
I have two theories – one is that the J-Head has a shorter melt zone so the head has to be hotter to get the plastic up to temp fast enough. The shorter melt zone is generally a good thing since I think the long one on the MG hotend led to a lot of my filament jamming.
The other is that since the thermistor goes into a hole in the metal while with the MG it is just taped to the side, the thermistor reads a hotter temp for the same actual temp, so to achieve the same actual temp you have to set the temperature higher on the J-Head.
On the MG hotend, I usually print at 180*C for PLA, 230 for ABS.
On the J-Head, I print at 200 for PLA, 245 for ABS.
I just had to reprint a couple of X ends for a couple of my friends – I had printed them at 230 but when I was boxing them up I noticed a gap on one of the layers, and when I pulled on it, the part fell apart. I think I didn’t have the plastic hot enough to bond, so I reprinted at 245. I may try even higher, maybe 255 or so.
The only problem with this is that around 270 you start to melt the hotend parts. I actually had a dream last night that when I woke up and checked on the all-night, higher temp print that I left running last night, my hotend would be destroyed and smoking. Thankfully that did not happen.
I don’t even want to think about the amount of times I’ve dreamed about 3D printing lately, in particular my printers and them causing me grief.
That’s another reason to print with PLA as much as possible, you don’t come too near the melting point of the PEEK and PTFE parts.
I think I’m done buying ABS but I have a couple of spools left that I want to use up. The last parts kit that I printed was 100% PLA and it looks great. There’s always been a concern about the motors getting hot enough to deform the motor mounts, but I don’t think they get that hot (62*C on my machine, 80*C if I use the hotter running motors). The J-Head needs a fan on it (and the fan is good for improved print quality anyway) so that’s not an issue either.