Changing Filament - Avoid problems before they begin!

[RolBer]

Good info, thanks.

[Ghosty]

i have found the best way to change filament is to just cut the old stock flush with the bit it enters the stepper part, then feed new ontop, let it feed till the new colour is coming out the nozzle, no blockages, no problems so far. as for the 2nd extruder when thats not being used i empty it fully (well till nothing comes out the nozzle)

[RobH2]

i have found the best way to change filament is to just cut the old stock flush with the bit it enters the stepper part, then feed new ontop, let it feed till the new colour is coming out the nozzle, no blockages, no problems so far. as for the 2nd extruder when thats not being used i empty it fully (well till nothing comes out the nozzle)

I used to do that too and even went as far as to take an exacto and drill a conical hole in the end of the part already in the extruder and then sharpen the end of the new filament. Then they would stay in alignment on the way in.

Once the filament in the extruder is past the hobbled bolt it doesn't get any "push" anymore. I was printing something that had a lot of retractions. It was pushing my new filament back up and leaving the lower filament without any "push" and causing problems.

Now what I do is turn the hot end down to 120C when I'm ready to change filaments. I let it sit for a few minutes and then I manually back the filament out slowly, mm by mm. After I've pulled about 30mm out I remove it at a normal speed by spinning the large gear. When it comes out it's usually the shape of the inside of the hot end.

What that does in one step is purge the hot end of most of the residual plastic and it also is a bit of a cleaning as it pulls any debris, dust or dirt out that might be in there. I keep filament cleaners on my filaments but I'm sure some debris slips by now and then. I talk about the process here ( http://3dprintboard.com/showthread.p...n+hotend+nylon) in post #8, as a solution to jams.

I think this is especially important if say I've been using ABS and switch to PLA. I print the ABS at 230C and the PLA at 195C. If there is any ABS left in the hotend when I put the PLA through at a lower temp, the ABS is not fully melted and jams can occur. The other scenario is also an issue. If I have printed PLA and now want to print Nylon I have to heat the hotend to 245C. PLA melts at 195C and by the time the residual PLA gets to 245C it can burn and become a hard knot. That can promote a clog.

Using this method has worked well and I like it better than the old way I did it, and, I used to like that old way. I feel this is better on a number of levels.

[Ghosty]

i see what your saying, but i only ever use pla (i cant stand the smell of abs melting).