The Printer Formerly Known as HPRINT – Part 2

About five months have passed since you last read about HPRINT, and in terms of the story behind it you’re about nine months behind.  Time to catch up!

When I arrived at Tech in August, one of the first things I did was try out the new gantry components and was pleased to find that they worked fairly well, but I would need to seriously alter the extruder carriage and pulley layout to ensure smooth operation.  At around the time I was working on the CAD for that, the workload of classes hit and I was forced to put off further work on the machine until around late November.  Until that time, the printer – which some Undergraduate Lab Instructors had begun referring to as Gigantor due to its titanic frame – collected a fair bit of dust.

When I began to work on it again, I focused on one of the major issues everyone has to contend with building an H-gantry:  skew.  When an H-gantry carriage moves on any diagonal direction, unbalanced forces exist on the ends of the gantry itself, resulting in skew.  This is of course a very bad thing for precise applications like 3D Printing, as it ruins positional accuracy.  The only way around this is to have a structure that does not in any way permit skew, so I set about to design just that.

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Above is a picture of the updated gantry assembly as a CAD model, one of the gantry ends, and as it existed early on in the semester.  The increased length, a shift to brass bushings, and bracing using aluminum angle had a dramatic effect on overall rigidity.  Unfortunately, due to the level of inaccuracy present in the consumer machines used to create the parts they were effectively unusable: slight contraction of the plastic during printing had caused them to curve just enough to bind horribly on the linear rods.  It was at this stage where I decided to make the switch to a standard gantry setup, with one motor added to control the travelling X-Axis.

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After a few iterations and test prints, the result was a fairly robust and simple set of parts which would work as desired (and a lot of discarded and spare components lying on the conveniently-located build surface).  Though it is no longer uses an H-gantry, the balanced force from two motors on the Y-Axis can handle the now heavier gantry quite well.  A little bit more assembly and wiring later:

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And it was finally in a state where I could begin to really adjust firmware settings.  Though by that time, I was a bit busy with other things:

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The wait for the final part of – for lack of a better working name – Gigantor’s construction and setup will be considerably shorter than the wait for the second.  Until then, here’s a preview:

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-Jeff

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