Solid printing at last!

The hot end is assembled and fitted.  The filament drive extruder is assembled and fitted.  Even the LCD panel is fitted and (mostly) working.  this means that I can now print solid plastic parts.  In theory.  In practice, there are teething troubles.

  1. Levelling the bed.  Layers of plastic must be deposited at thicknesses of less than 0.35mm.  If the print bed is not level with respect to the print head motion, then it might, at different points on the bed area, print in mid-air (bad), or drive the print head into the print bed (bad), or simply print too thin a layer (bad but not terrible).  I’ve made a bit of a rod for my own back by giving my print bed three adjustment screws, but it is doable.
  2. Calibrating the print head motion.  This is still not quite right.  Assuming that the glass print plate is flat (and it’s float glass, so it should be), then my print head seems to move in Z (the vertical axis) slightly as it travels over the X and Y axes.  It’s as if the notional Z-plane is a very slight dome, higher in the centre.  This makes printing larger objects (more than about 100mm diameter) impossible at present.  It’s undoubtedly fixable, but may require a software tweak.
  3. Ensuring that the extruder drive doesn’t slip.  This has been a big problem.  Forcing a plastic filament down a PTFE tube and through a heated nozzle only a fifth of its diameter actually takes quite a bit of force.  The extruder drive pushes the filament by pressing a rotating knurled wheel against it.  The problem is that if the resistance from the nozzle is too great (for example, if the clearance between the print head and the print plate is too small, leaving no room for the hot plastic) then the knurled wheel rotates and grinds into the filament rather than pushing it along.  This means no molten plastic at the print head, and a failed print.  Careful adjustment of the force on the filament seems to have fixed this for now.

Having said all that, I have actually managed to print something:

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It’s not really that impressive.  A simple 10mm cube, cunningly printed in blue plastic on blue masking tape, so it’s hard to see.  Careful positioning of the ruler ensures that you can’t see that it actually came out 9mm in each dimension.  Did I mention that calibration is still an issue?

Flushed with success printing a tiny cube, I thought I’d try something bigger.  One of the printer’s own components, in fact.  The next picture shows two versions of the pen-holder used to replace the hot end while I was testing.  No prizes for guessing which one I printed, and which came from  Rob’s printer.

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Still, it’s a start.  For scale, here is the part in the printer, just finished:

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Initially flushed with success, I spent the next few days completely unable to get the printer to do anything but produce failed prints.  Here’s the sort of thing I mean:

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The problem here is that the first layer of plastic hasn’t stuck properly to the print bed, leaving holes (not the round ones, they are deliberate).  Or possibly the extruder drive mechanism has slipped.  Or both.  Either way, it’s junk.  I have quite a few of those.  Gradual tweaking and experimentation has improved matters now, though, and I have managed to print out some reasonable parts:

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These are two copies of the same object (actually part of the print mechanism), using different layer thicknesses.  The further of the two uses thinner layers.  It takes longer to print, but is much more successful.  For scale, the holes you see in the parts are 3mm diameter.  These are quite small parts.  The layers in the better print are 0.2mm thick.  With a bit of sanding to remove the rough edges, this part should be quite usable.  It will be amusing to replace the printer’s parts with items it has printed itself.

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