RepRap: Blog

This is not a new idea (indeed, it's so old that I've forgotten if it was Simon or Nophead who first suggested it; apologies to the true originator if it was neither of them...). But a simple way to improve build quality is to start and end the outlines of parts from within the solid area that they surround. This avoids dwell problems at the start and finish of the outline, and wipes the nozzle on the interior of the part itself as the head moves off to the next outline. All the slightly dodgy blobs, dribbles and so on are left buried in the fill, and don't appear on the outer surface.

At the end of last week Ed and I realised that a simple way to do this is to use the hatch that fills the interior as a guide to what is needed. I've now implemented this in the Java Host software and checked it into the repository. On the right is the new code building my handy SMT-measuring tweezers. This type of object with its thin sections is notorious for generating lots of spurious bumps and string. As you can see there is the occasional lump (easily removed with a fingernail post build), but the quality is much better than before. And it works even better on chunky things like the coat hook.

The way the code works is to identify the extremal corner of the profile in the hatch direction. It then finds the nearest point in the hatch to that. From that hatch point it tracks through the hatch until it finds a reasonably long hatch line (where "reasonably long" == 10 mm or so). It then adds the hatch lines from the middle of that long segment to the outline polygon and deletes them from the hatch. There are other heuristics to deal with cases where it can't find a long bit and similar problems.

The effect of this is to start the outline within the solid (and the middle of a "reasonably long" hatch line is likely to be a sensible distance from the perimiter for that start), run to the outer edge having left dwell blobs and draggy starts in the middle of the solid, run neatly round the outline, and then move back into the middle again (without extruding) to finish.

It's always nice when you can make things better just by changing the software...

I'll play with it for a bit to check it works OK, then do a release.

Labels: blobs, build quality, heuristics, string

I saw these door handles on the bench today from Adrian and Nophead and thought 'photo'. From left to right: old to new. Its exciting to think about where this trend leads!

Labels: build quality, Door handle

Ed and I have been experimenting with various strategies to improve build quality. One problem is bits of polymer sticking to the head and then dropping onto the build and messing it up. Another is the fact that if you run the acorn-nut nozzle (left above) too close to the surface it smears the molten polymer all over itself, and then re-deposits some of that later where you don't want it.

I made up the nozzle on the right. It is 1.5 mm diameter at the end, with an 0.5 mm diameter through hole. With this in place of the acorn nut, you can run the nozzle over the surface to sweep it flat without pushing the polymer where you don't want it.

It is a bit more complicated to make than the acorn-nut nozzle (which just needs you to drill one small hole in an off-the-shelf part, of course). But it works significantly better.




To clean the new nozzle, we've added a toothbrush along with a nose-wipe cycle to the host software. This keeps the crud off the nozzle by wiping it back and forth at the start of each layer.

Now. How do we clean the toothbrush?...

Labels: build quality, cleaning, nozzle