Blobless Printing With Velocity Extrusion

velocity

The current crop of 3D printers are technically four-axis machines, with three axes of movement and a fourth for the position of the filament. [Bas] had an entirely different idea – why not link the speed of the extruder to the speed of the nozzle? It turns out this technique gives you more ‘plasticy-looking’ prints and a vast reduction in blobbiness.

[Baz] has been working with LinuxCNC, a BeagleBone Black and the BeBoPr-Bridge cape, and there’s been a lot of development with that system in turning many straight lines into one smooth arc. This led him to adjusting the flow rate of a nozzle while the printer is running, but this is difficult if the extrusion is controlled by position as in a traditional printer setup. A new configuration was in order.

What [Baz] ended up with is a config that calculated the speed of the extruder based on the speed the nozzle is moving over the print surface. This gave him the ability to add live nozzle pressure adjustment, and as a result, a near complete disappearance of the little blobs that appear at the start of each layer.

For a well calibrated machine, it’s only a small difference between the ‘normal’ and ‘velocity’ methods of controlling an extrusion rate. It’s a noticeable difference, though, and one that vastly improves the visual quality of a print.

 

DIY Filament: The Filabot Wee

filabotwee

Now there’s yet another option for making your own 3D printer filament: the Filabot Wee. It looks like their once open source model that they pulled from Thinigiverse earlier this year has received a significant makeover, though we aren’t sure what parts may have changed. (EDIT: Filabot says the Wee is still open source, and that once they’ve updated the files they will be available again.)

As you would expect, the Wee has a PID temperature controller and is capable of extruding both ABS and PLA pellets into either 1.75mm or 3mm-diameter filament. Speed varies depending on materials and thickness, but can reach 5 to 20 inches per minute of filament extrusion. Though the Filabot gang is selling the extruder as a kit, you can probably save a few bucks if you have access to a laser cutter and some other basic materials.

You should expect to spend more for Filabot parts ($649) than you would for the original Lyman extruder, though perhaps a more fair comparison would be the new third version of the Lyman extruder, whose bill of materials approaches $900. Considering Lyman’s recent comments that indicate an extrusion rate of 40-50 inches per minute, the extra bucks may be worth it. You can check out a demonstration video of the Filabot Wee after the break.

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Accurate temperature control of your 3D printer extruder

[Tim] is working on building a 3D printer and using it as an excuse to learn as much as he can. The first big issue he tackled was accurate temperature control, so he made an interesting write-up on how to characterize the thermal properties of an QU-BD extruder’s hot end and use that information to create a control algorithm for the heater.

The article starts with a basic thermal model and its corresponding formula. [Tim] then runs several tests where he measures the heater and extruder tip temperatures while switching on and off the heater. This allows him to figure out the several model parameters required to design his control algorithm. Finally, he tweaked his formula in order to predict the short term future so he can know when he should activate the heating element. As a result, his temperature is now accurately controlled in the 200°c +/-1°c window that he was shooting for.

Chocolate extrusion printer is halfway to making s’mores

Chocolate has got to be one of the worst choices as a printing medium. It’s extremely fussy when it comes to melting point, and even in the right state the flow of the material is not going to play nicely with high-resolution designs. With this in mind, we applaud the progress the student team from Carnegie Mellon University has made with WonkaBot,  their chocolate extrusion printer.

Unlike the syringe-based paste extruder from last month, this offering uses an auger to push chocolate through a heated printer head. They’re using it to print designs on graham crackers. We love the UI they came up with for the task. It uses a virtual graham cracker as a canvas on your laptop and allows you to use the touchpad or mouse to draw your design. That input is then converted to g-code and sent to the CNC machine for printing. See it in action after the break.

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RepRap acrylic extrusion using hotbed

[Nophead] started the year off by successfully extruding acrylic using a RepRap machine. The problem when working with this material is that when the hot ooze hits the cold air the printed material tends to warp, badly. [Nophead] raised the ambient air temperature around the part being extruded by replacing the bed of the RepRap machine with a heated aluminum plate.

We took at look at his build details for the hotbed. The plate itself is aluminum that he had milled by a machinist friend of his. It looks like the heat is produced by a network of power resistors bolted and soldered to the bottom of the plate. The original idea was to produce a controllable SMT soldering platform. Unfortunately this heating method doesn’t have the power needed to raise the temp quickly but that failure turned out to be a RepRap success.

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