Tips on switching feeds

Recently, I switched from white PLA (4043A ) to black ABS. When going from PLA to ABS, it seems like the change in the extruded filament happened a lot faster than when I went back to PLA. After swtiching back to PLA, black ABS was still being extruded while printing 4 large pieces out that take up the whole bed after purging the extruder so that mostly while was coming out and printing several test pieces (single walled box and hexagon).

I was wondering if others can share their tricks for switching feed. I thought that the problem with the ABS-PLA swtich is that PLA at the temperature that I was using to extrude (220-240C) is probably less viscous than ABS and so it doesn't efficiently push it out. I'm guessing that pools of ABS are being bypassed by the flow. I thought that if I had a 3 mm PTFE rod, then I can push it into the extruder after pulling out the ABS to push most of the remaining plastic at the tip out. Has anyone tried this?

Yes pushing a 3mm rod gets the majority of it out. Another way to clear it out is by attaching a car tyre pump to the top of the extruder barrel. I tried it once and it worked well. Normally though I just run a couple of feet of filament through at the higher of the two temperatures. I.e. I run PLA at ABS temperature until all the ABS has gone.

How long it takes to flush through probably depends on how long the melt zone is and the shape of it. I.e. if there are any gaps plastic can hide in it will be hard to flush it clean.

---

[www.hydraraptor.blogspot.com]

Thanks. Now I just have to find 3mm diameter PTFE filaments.

A couple of feet of filament? I probably used less than that running the tests before printing the parts so the rest came in the first few layers of the parts I needed. I guess I was being a bit of a miser. Luckily, I don't need these parts to look good.

Edited 1 time(s). Last edit at 03/21/2011 01:12PM by brnrd.

I just use a metal rod. 3mm PTFE rod is probably too soft to push.

---

[www.hydraraptor.blogspot.com]