Oil - the cause of, and solution to, all of life's problems.

Another week gone and there was not much to show for it. The extruder stopped working again, of course. No amount of fiddling with it would make it go for more than a layer or so of any print, which is really frustrating when one needs just one more print (ok, admittedly a pretty large one) to dump the extruder for good.

However I did solve some other niggling issues with the reprap. I figured out how to get a set square in between the X and Y axes and satisfactorily set them up perpendicular to each other; it worked really well until yesterday when there was a somewhat catastrophic failure and I had to go through the whole mess of disconnecting the X belts and realigning all over again. It *seems* to be robust now that it's back together, but I want to replace the bearing blocks that mount the X carriage onto the Y as they're extremely fiddly and will bind if they're done up too tight... or shed a bolt or two, go loose and bind anyway.

I also figured out a way of having the reprap itself tell me how much backlash there is in each axis. I modified the firmware so that it keeps track of how many steps it takes to move off an endstop - since there only needs to be one step's worth of actual movement away from an endstop to deactivate it, any extra must be backlash. I measured 5 steps of backlash on the X axis and 1 step on the Y axis, which seems to be about right; it comes out to 0.625mm on X and 0.125mm on Y. Plugging those values into Skeinforge's Lash module (well, half those values really) made a marked improvement... in the partial layers I could get out of the extruder, of course.

I noticed that the extruder seemed to have more trouble when the print head was in the middle of the bed as opposed to at the origin, which is closer to the spool and so the filament is pulled to the side less. I used a long bolt and a piece of acrylic with a couple of holes drilled in it to make a filament guide that sat a couple of inches above the extruder and ensured the filament was more vertical as it went into it. I also put some oil into a folded up Subway paper napkin and put it above the guide to oil the filament as it passed by.

Still no good. Gaah! Screw it, I'm just going to squirt heaps of oil (well, a few drops) directly into the top of the extruder. I don't care any more, and I've tried everything else.

Wait a second, that worked?

Two and a half hours later...

:D

Teething problems...

Things have not been all rosy in reprap land (what else is new?) The extruder started playing up again, and all the prints so far have come out elongated. The stretching isn't just in X or Y either, which would point to an easily addressed calibration problem - instead it was along the 45 degree line. There's only one explanation for that - my cartesian bot was a parallelogram ;_;

After some thought I figured out that I could move the belt on one end of the X carriage back by one tooth to change it's angle with respect to Y. This seems to have cured the lean mostly (although I might still move it back one more tooth) however circles are still coming out squished in X. And it's not a calibration issue, because a simple square comes out perfectly, and smaller circles are more strongly affected than larger ones.

I discovered what I believe to be the answer by watching the reprap doing the crosshatched infill on the large gear pictured at the top of this post. The left pattern in the diagram is what I should be seeing, but I was getting the right pattern instead. The bad pattern is being caused by backlash on the X axis. It might be caused by a loose grub screw on the X stepper drive shaft, or it might be a less easily corrected fault. Skeinforge has a backlash-mitigation option available; if I can't solve the problem mechanically, I'll solve it in software.

Speaking of Skeinforge, I'm slowly coming to grips with more of the obscure functions it provides. It's ridiculously powerful but it's hell trying to understand what each option actually does. Additionally, certain features are hidden in places that one wouldn't normally expect to find them. I finally found the option to shift the starting point of an object in the Multiply section - I just set it up to print one copy of the object, and I configured the other options there to automatically centre the object in the middle of the print bed. That solved the negative-axes problem once and for all.

And the extruder? I got fed up with it and tightened the springs down as far as they can sensibly go. And it stopped misbehaving. But I'm still going to replace it with a Wade's extruder as soon as possible. I've printed out a couple of parts for it already - hence the large gear :)

More prints!

More things printed! I printed a couple more minimugs today, one which failed part-way through, and one which completed essentially perfectly!

I also printed a whistle - which failed quite unexpectedly, squashed over to the left. It turns out that skeinforge happily works with objects that extend into the negative axes, and the whistle has a lanyard loop that extends into negative X. Each time the reprap tries to move into the negative region, it hits the endstops and the origin is reset, pushing subsequent layers to the right. We ended up with a straight lanyard hole and a curved whistle :P

I also attempted to print a classical 3d hypercube projection (two wireframe cubes joined at the corners) but that object started 10mm above the print bed! I need to find out if Skeinforge can recalculate the position of an object to put it's bounding box at (0,0,0), or if I need to write something myself.

(thanks to tj for the photo)