Nov.5, 2014
Over the last year, a small team of FDM enthusiasts based in El Paso, Texas has been refining and testing a dual filament FDM print head they call the X-Truder.
The lightweight and compact head has many desirable features such as 2 all-metal 315C hotends, ribbon cable connectivity, a high torque NEMA 11 motor, integral fan, servo driven extruder lifting etc.
"We wanted to design and market a print head for Makers who are looking to upgrade their existing 3D printer," explained David Williams, Praxis3D team member. With the ever increasing number of installed 3D printers, they're hoping to tap into a very large market.
At the heart of the X-Truder lies two all-metal extruders that were analyzed using thermal modeling and refined over several rounds of prototypes.
"Running PLA in a non teflon-lined extruder is a challenge and requires a smooth ID finish and a short thermal transition zone. Our combination of stainless steel tubing, copper heat sinking and a high flow 40mm fan achieves the goal.
We're able to lower the temperature over a very short length," adds thermal designer Frank Mercado. Their extruder was also tested with materials such as ABS and PC, which, according to the company, don't have the same issues of jamming but do require much higher temperatures.
To demonstrate their design efficiency, they made a small video of hand holding their extruder 6mm from the heatblock, feeding PLA at 230C.
Another goal they set was to make the X-Truder very compact, so the team chose a small stepper motor to drive both filaments. Their filament drive system doesn't use bolts and springs to achieve traction, but forces the filament through a fixed pinch wheel gap. Precision teeth are cut into the motor's 5mm diameter shaft which provides enough traction and avoids tear outs. The drive system also disengages from the idle filament, which means easy filament loading and unloading, even while the head is printing. Notes David, "an interesting benefit to using a smaller motor is that strip outs are almost non-existent. We've had situations where the nozzle is pressed against the print bed glass or the extruder temperature is too cold for the material, and the motor just pops and loses steps. Our motor has plenty of power to drive the filament, but not enough to tear apart the filament or jam up the filament pathways."
Praxis3D incorporated extra circuits into the 18 inch long ribbon cable assembly, allowing makers to design and attach their own accessories to the X-Truder, such as bed leveling probes, fans, other servos, endstops, and more. To simplify the connections between the head and customer's electronics, they're including an adapter PCB with screw terminals for each circuit. Additionally, the head has bright white LEDs for lighting the work area.
The Praxis3D team also tackled a common issue with dual extruder machines, being nozzle drag and collisions with the printing part. To avoid those situations, they designed in nozzle retraction or lifting, which is handled by a metal gear micro servo and cam arrangement. During their refinement rounds of prototyping, they were able to achieve about 1mm of nozzle lifting, raising the idled extruder about 4 layers above the printing part.
According to the team, "the cam and servo arrangement is an elegant and simple mechanism, easily controlled by modern electronics, and we've yet to identify the mechanism's life span. We set up an experiment to test the drive system, the retraction, and in general, the whole head, and we were extruding pounds of PLA, with head switching every few minutes, plus warm up and cool down cycles. We ran 6 spools of plastic through the head, then ran a test that just cycled the retraction servo. We run that program for 100k changeovers, then inspected the parts closely and found no wear. We decided to stop testing and since that time, the same head and servo continue working."
To simplify the mounting of the X-Truder within the many different printers, Praxis3D designed their Klix mounting bracket. It incorporates powerful neodymium magnets and precision conical features to firmly and repeatably mount their head. The Klix mounting bracket is included with the X-Truder and they will also make them available on their website in the near future.
The X-truder has been launched on Kickstarter, and the early bird price is $250, including the X-truder head assembly, an interface PCB, and the ribbon cable. Head over to their Kickstarter campaign and check out the details.
Posted in 3D Printer Accessories
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Brian wrote at 11/5/2014 4:45:15 PM:
How much time did they waste on that kickstarter video "cartoon"... I was expecting to see the X-Truder in action.
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