Multimaterial research

One of our customers, Dr Michael Fairhurst, has had a very neat and simple idea for how to implement a multi-material RepRap.  It is to treat the filament as a railway train approaching points, and to design the filament path to allow filaments to merge into a single hot end.  Here’s my implementation:



Three of our standard Bowden tubes lock into a small printed part that merges the filament streams.  To change colour you simply retract the current filament past its merge point then feed another one in its place.  Suddenly almost all the problems of multi-head machines go away.  There is only one Z height to worry about.  There is no dribble from unused heads.  And so on.  On a filament change you can purge the old material in infill before doing the outside which gets to be seen.  Or you can build a small sacrificial tower away from the print to purge the nozzle.

I have tried this by hand with the hot end at temperature, and it seems to work well.  But a real test will need a proper print with hundreds of retractions, not just the five I did as an experiment.  I am concerned that pieces of filament may trail behind the retraction on pulled-out strings and cause blockages.  I had thought that a way to avoid this would be to drop the hot end temperature to about 100oC before retracting to ensure the filament (PLA) was coherent enough to all come away at once.  But that actually seems to jam a bit because the molten end can be a little swollen and inflexible.  Optimisation experiments are needed…

Meanwhile, Michael has a design for an integrated three-motor drive and filament guide:

Multi-head-cadMulti head printer head mounting (20140414)

The nice thing about all this, of course, is that the merged guides don’t have to lie in a plane.  You could print rings of them and have lots of feeds all going into the same head.  And when I say lots, I do mean 20…


Adrian Bowyer