Sunday, January 17, 2016

DIY Filament Factory

Winder box with Filastruder on top
As a frequent 3D printer user, I sometimes go through a spool of filament... well... faster than a redneck goes through second cousins at a family reunion.  While the price of filament has dropped significantly in recent years, raw plastic pellets can still be bought for less than one-third the cost.

To take advantage of this, a number of solutions exist for making one's own filament, including the Filastruder, a kit I received a prior Christmas.   Cleverly designed from largely ordinary hardware, the device extrudes filament by squeezing plastic pellets with an auger bit down a heated length pipe and out a small nozzle.

I'd always had mixed results using the Filastruder, however, as reliable use requires suspending it in the air over a large open space.  Otherwise, that the fragile molten filament can catch on furniture or itself, causing the resulting product to kink, snag, and be otherwise unusable.  This made it a real hassle to use, especially since even a slight air movement from opening a door or walking by could disturb the filament. With little Monkeys about, this was not a realistically achievable scenario.

For a more convenient system, I decided to try making a simple filament winder that could take up the filament as it is produced, keeping it neat and consistent.  While a commercial winder kit exists, I could justify neither the cost nor large wall hanging space it requires when set-up.  Instead, I chose to make one of my own design; one that didn't require the same finicky electronics.  It would also be a challenge which added to the fun.  Lastly, I came up with the idea of building it into a handy portable case that could house both itself and the Filastruder, keeping them free of dust and out of the way when not in use.

I created a frame for a simple plywood box, roughly 20 inches square and 6 inches thick.  I stained it and added a leather handle and some brass hardware, fancying that this gave it the appearance of some bizarre 19th century science experiment or instrument of medical quackery.

The toughest part of the design was finding a way to sense slack in the filament without disturbing the path of the filament itself.  As the new filament comes out molten, I found that even the lightest micro-switch I could find would transmit too much force back up the filament and cause a kink near the nozzle opening.

Other winders use linear sensors, but they require a microprocessor and more complexity, which I hoped to avoid. After trying mercury switches and considering magnetic reed switches and other sensors,

I settled on a lightweight 3D-printed "see-saw" rocker that I weighted down slightly on one side.  The filament moves in a loop down the left side of the box, across the bottom, and up the right side.  When the filament develops too much slack, the bottom of the loop pushes down on a curved acetate surface glued to one side of the rocker. This lifts up the other side, raising a shutter that exposes a CDS-cell light detector to a single LED light source.

The cell is connected to a solid state relay that drives a small gear motor and the take-up spool.  I also added a cheap $5 PWM motor speed control board to allow fine-tuning of the motor speed.

To evenly guide the filament onto the spool, the filament passes through a short length of tubing mounted onto a hinge.  As the hinge moves, the filament comes out at a different place on the reel, keeping it from bunching up in one place.

The hinge, in turn, is linked to a carriage, that moves up and down along a worm gear (threaded rod) driven by a second gear motor.  Two momentary limit switches keep the carriage from moving too far in either direction. They simply switch on and off a DPDT latching relay, wired in a way (one on, one off) so that the motor reverses direction when either switch is hit.

After my initial tests, I also added a small, spring loaded clamp to keep the filament under tension.  This was needed to keep the filament tight on the reel.

Here is the completed winder case.  When in storage, the Filastruder fits neatly inside with hanging space for an empty or full filament spool.

When I'm ready use it, I simply set the extruder on top of the case and pass the new filament down through a hole in the top and loop it round to the winder inside.

I was surprised how well it worked right off the bat.  The rocker assembly tends to stay right on the edge between on and off, moving ever so slightly to periodically activate the take-up motor.  The movements are so small that the filament path moves very little, leading to the most consistent filament than I've ever made before.

I've already successfully used it to create two one-pound (half-size) spools. I'll still probably buy some filament, particularly for special colors and specialty plastics.  When I need simple black or white filament, however (the colors I use the most), from now on I'll probably just make my own.

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