Code Errors

I ran out of ABS plastic in mid-December, but fortunately I had a source of PLA lined up so that I could adapt my system and keep going.  Unfortunately, getting PLA to extrude turned out to be much harder than I expected.  It wasn’t until last friday that I discovered that a little bit of oil would fix my problems.

The PLA I have is 4042D.  What I initially observed was that no matter what I would do, the PLA would eventually get jammed and I would have to tear my extruder apart to get it cleaned up and working again only to have it fail minutes later.

I ruined a PTFE barrier trying to force the PLA through by hand and I broke a heater barrel trying to unscrew a nozzle with solidified PLA in it.  I’ve learned to be very careful now.  Whenever the extruder gets jammed I take it apart piece by piece with the heater on (wearing good gloves) to get the PLA out without damaging its shape.  From this excercise I have learned that the PLA always melts in the PTFE section.  Even using a steel barrel with a heat sink.  I haven’t tried narrowing a section of steel yet, which may give me the short transition zone that nophead recommends.

In hopes of narrowing down the problem, I removed some components from the equation.  First was the extruder motor and drive block.  I simply pushed the filament by hand until it would move.  What I found here was that as long as I continously moved the filament it would not get jammed, but if I stopped for a few seconds I could not get it started again no matter how much I pushed.  I could pull the PLA back out and then force the liquid part out using a steel tool without much effort.

I then removed the nozzle so that all I had left was the PTFE barrier and the heater barrel.  I observed the same behavior.  The pressure I was feeling jam up the extruder was not from the nozzle.

I decided to try something I had read about in the reprap blog.  I coated about a foot of PLA with oil and repeated my simplist experiment.  At this point I knew exactly what to do to cause a jam.  Heat up the PLA, extrude a little be, stop for a few seconds and everything is jammed.  Well, with the oil it didn’t jam, it just kept on going.  I did a few other tests including cooling the PLA after stopping and then reheating it with no problems.  The oil solved everything.

Obviously I wasn’t about to coat every inch of the PLA by hand.  Instead I put a small hole in a piece of fabric (cotton, but I think anything will do), bolted it to the top of my extruder and soaked it in oil.  I ran the PLA through the hole to deposit oil on it as it enters my extruder.

This worked great as long as I kept the fabric wet with oil.  This required my attention every 15 minutes, which was annoying.  It turns out that my MDF extruder block was soaking up most of the oil and so I put a plastic liner between the fabric and the extruder block.  Now it can run for hours without a refill, although it does tend to dry out between uses.

I am using engine oil, 10W-30, I believe.  I bought the wrong stuff for my car once and so I have a quart of it lying around.  I thought about using vegtable oil, but I think it would smoke at my working temperatures and I don’t need my reprap smelling more like waffles than it does just running PLA.

At first I was extruding at 210 C and getting good results.  I found that to print a working whistle I had to reduce this to 180 C.  At 180 C the raft does not stick to my MDF bed, so I have to print the raft at 210 C.

I’ve also discovered that PLA will get into any gaps.  This means that every time you take a part off (nozzle or PTFE) and screw it back on it won’t go on tight with the PLA blocking the thread.  I have to screw it on and then heat it up and then tighten it.

This entry was posted on Wednesday, January 20th, 2010 at 8:45 pm and is filed under RepRap. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.