Adding Remote Control To The Elegoo Mars Pro

October 30, 2020 by Tom Nardi 5 Comments

Recent price drops put entry level masked stereolithography (MSLA) resin 3D printers at around $200 USD, making them a very compelling tool for makers and hackers. But as you might expect, getting the price this low often involves cutting several corners. One of the ways manufacturers have made their machines so cheap is by simplifying the electronics and paring down the feature set to the absolute minimum.

So it was hardly a surprise for [Luiz Ribeiro] to find that his new Elegoo Mars Pro didn’t offer WiFi connectivity or a remote control interface. You’re supposed to just stick a USB flash drive into the printer and select the object you want to print from its menu system. But that doesn’t mean he couldn’t hack the capability in himself.

If this were a traditional 3D printer, he might have installed OctoPrint and been done with it. But resin printers are a very different beast. In the end, [Luiz] had to develop his own remote control software that worked around the unique limitations of the printer’s electronics. His software runs on a Raspberry Pi Zero and uses Linux’s “USB Gadget” system to make it appear as a flash drive when plugged into the USB port on the Elegoo Mars Pro.

This allows sending object files to the printer over the network, but there was a missing piece to the puzzle. [Luiz] still needed to manually go over to the printer and select which file he wanted to load from the menu. Until he realized there was an exposed serial port on control board that allowed him to pass commands to the printer. Between the serial connection and faux USB Mass Storage device, his mariner software has full control over the Mars Pro and is able to trigger and monitor print jobs remotely.

It might not offer quite the flexibility of adding OctoPrint to your FDM 3D printer, but it’s certainly a start.

Bringing High Temperature 3D Printing To The Masses

October 28, 2020 by Tom Nardi 77 Comments

Despite the impressive variety of thermoplastics that can be printed on consumer-level desktop 3D printers, the most commonly used filament is polylactic acid (PLA). That’s because it’s not only the cheapest material available, but also the easiest to work with. PLA can be extruded at temperatures as low as 180 °C, and it’s possible to get good results even without a heated bed. The downside is that objects printed in PLA tend to be somewhat brittle and have a low heat tolerance. It’s a fine plastic for prototyping and light duty projects, but it won’t take long for many users to outgrow its capabilities.

The next step up is usually polyethylene terephthalate glycol (PETG). This material isn’t much more difficult to work with than PLA, but is more durable, can handle higher temperatures, and in general is better suited for mechanical parts. If you need greater durability or higher heat tolerance than PETG offers, you could move on to something like acrylonitrile butadiene styrene (ABS), polycarbonate (PC), or nylon. But this is where things start to get tricky. Not only are the extrusion temperatures of these materials greater than 250 °C, but an enclosed print chamber is generally recommended for best results. That puts them on the upper end of what the hobbyist community is generally capable of working with.

Industrial 3D printers like the Apium P220 start at $30,000.

But high-end industrial 3D printers can use even stronger plastics such as polyetherimide (PEI) or members of the polyaryletherketone family (PAEK, PEEK, PEKK). Parts made from these materials are especially desirable for aerospace applications, as they can replace metal components while being substantially lighter.

These plastics must be extruded at temperatures approaching 400 °C, and a sealed build chamber kept at >100 °C for the duration of the print is an absolute necessity. The purchase price for a commercial printer with these capabilities is in the tens of thousands even on the low end, with some models priced well into the six figure range.

Of course there was a time, not quite so long ago, where the same could have been said of 3D printers in general. Machines that were once the sole domain of exceptionally well funded R&D labs now sit on the workbenches of hackers and makers all over the world. While it’s hard to say if we’ll see the same race to the bottom for high temperature 3D printers, the first steps towards democratizing the technology are already being made.

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Take This 3D-Print Post-Processing Method With A Grain Of Salt

October 27, 2020 by Dan Maloney 20 Comments

There’s a lot of folklore around post-processing of prints from FDM printers. Proponents swear by their methods, which are generally intended to either strengthen the part or to improve its appearance, or both. But do they actually work?

Knowing that a collection of anecdotes is no substitute for actual data, [Stefan] from CNC Kitchen has again performed some valuable experiments, this time testing the strength of parts that have been annealed in salt. This was a follow-up to his recent experiments with baking prints after entombing them in plaster, which yielded mixed results in terms of strength gains. Viewers commented that common salt makes a good medium for annealing prints, so he set about finding the right kind of salt. It turns out that the finer the grain, the better — powdery salt packs tighter and leaves little space for the softened plastic to flow — but that powdery salt is not easier to find. He ended up making his own by pulverizing table salt in a blender. He also had to play around with temperatures and times until coming up with a good process.

The results are impressive. PETG, ABS, and two varieties of PLA prints tested with force applied perpendicular to the print layers all showed marked increase in strength after breaking, to the point of nearly matching the strength of parts printed with the layers parallel to the stress. As with the plaster, parts were printed at 100% infill; a Benchy printed at 20% was notably unseaworthy after annealing. Surface finish on the annealed parts is an interesting combination of pitting with white residue — not unattractive but still a bit weird.

Salt annealing might be a bit cumbersome, but it’s a neat method to add to all the other post-processing tricks that people have come up with for their 3D prints. Continue reading “Take This 3D-Print Post-Processing Method With A Grain Of Salt” →

Improved Flexible Build Plate For SLA Is Ready To Rock

October 26, 2020 by Donald Papp 25 Comments

The Elegoo Mars is an affordable SLA (resin-based) 3D printer, and there are probably few that have seen more mods and experimentation than [Jan Mrázek]’s machine. The final design of his DIY flexible build plate is a refinement of his original proof of concept, which proved a flexible build platform can be every bit as useful on an SLA printer as it is for FDM; instead of chiseling parts off a rigid build platform, simply pop the flexible steel sheet off the magnetic base and flex it slightly for a much easier part removal process. His original design worked, but had a few rough edges that have since been ironed out.

We love how [Jan] walks through all of the design elements and explains what worked and what didn’t. For example, originally he used a galvanized steel sheet which was easy enough to work with, but ended up not being a viable choice because once it’s bent, it stays bent. Spring steel is a much better material for a flexible build platform, but is harder for a hobbyist to cut.

Fortunately, it’s a simple job for any metal fabrication shop and [Jan] got a variety of thicknesses cut very cheaply. It turns out that the sweet spot is 0.3 mm (although 0.2 mm is a better choice for particularly fragile parts.) [Jan] also suggests cutting the sheet a few millimeters larger than the build platform; it’s much easier to peel the sheet off the magnetic base when one can get a fingertip under an edge, after all.

The magnetic base that the steel sheet sticks to is very simple: [Jan] converted a stock build platform by mounting an array of 20 x 20 x 1 mm magnets with 3M adhesive mounting tape. He was worried that resin might seep in between the magnets and cause a problem, perhaps even interfering with the adhesive; but so far it seems to be working very well. Resin is viscous enough that it never penetrates far into the gaps, and no effect on the adhesive has been observed so far.

Watch how easily parts are removed in the short video embedded below, in which [Jan] demonstrates his latest platform design.

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Polymer Networks Make Better 3D Prints

October 17, 2020 by Al Williams 5 Comments

Biological machines such as human and animal bodies are quite incredible. Your body seamlessly incorporates materials as different as muscle, bone, and tendons into an integrated whole. Now Texas A&M researchers think they can imitate nature using polymer networks that have a tunable stiffness. As a bonus, similar to biological devices, the material spontaneously self-heals.

The trick relies on the Diels-Alder reaction which is a cycloaddition reaction of a conjugated diene to an alkene. Diels-Alder-based polymers or DAPs will bond together even when they have different physical characteristics and they undergo a reversible reaction to heat which offers shape-memory and healing capability.

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Adding Crush Ribs To 3D Printed Parts For A Better Press Fit

October 15, 2020 by Donald Papp 18 Comments

[Dan Royer] shared a tip about how to get a reliably tight fit between 3D printed parts and other hardware (like bearings, for example.) He suggests using crush ribs, a tried-and-true solution borrowed from the world of injection molding and repurposed with 3D printing in mind. Before we explain the solution, let’s first look at the problem a little more closely.

Imagine one wishes to press-fit a bearing into a hole. If that hole isn’t just the right size, the bearing won’t be held snugly. If the hole is a little too big, the bearing is loose. Too small, and the bearing won’t fit at all. Since a 0.1 mm difference can have a noticeable effect on how loose or snug a fit is, it’s important to get it right.

Crush rib locations highlighted with blue arrows.

For a 3D printed object, a hole designed with a diameter of 20 mm (for example) will come out slightly different when printed. The usual way around this is to adjust printer settings or modify the object until the magic combination that yields exactly the right outcome is found, also known as the Goldilocks approach. However, this means the 3D model only comes out right on a specific printer, which is a problem for a design that is meant to be shared. Since [Dan] works on robots with 3D printed elements, finding a solution to this problem was particularly important.

The solution he borrowed from the world of injection molding is to use crush ribs, which can be thought of as a set of very small standoffs that deform as a part is press-fit into them. Instead of a piece of hardware making contact with the entire inside surface of a hole, it makes contact only with the crush ribs. Press fitting a part into crush ribs is far easier (and more forgiving) than trying to get the entire mating surface exactly right.

Using crush ribs in this way is a bit of a hack since their original purpose in injection molding is somewhat different. Walls in injection-molded parts are rarely truly flat, because that makes them harder to eject from a mold. Surfaces therefore have a slight cant to them, which is called a draft. This slight angle means that press fitting parts becomes a problem, because any injection-molded hole will have slanted sides. The solution is crush ribs, which — unlike the walls — are modeled straight. The ribs are small enough that they don’t have an issue with sticking in the mold, and provide the mating surface that a press-fit piece of hardware requires. [Dan] has a short video about applying this technique to 3D printed objects, embedded below.

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Put That New Resin Printer To Work Making PCBs

October 9, 2020 by Dan Maloney 33 Comments

With all the cool and useful parts you can whip up (relatively) quickly on a 3D printer, it’s a shame you can’t just print a PCB. Sure, ordering a PCB is quick, easy, and cheap, but being able to print one-offs would peg the needle on the instant gratification meter.

[Peter Liwyj] may just have come up with a method to do exactly that. His Instructables post goes into great detail about his method, which uses an Elegoo Mars resin printer and a couple of neat tricks. First, a properly cleaned board is placed copper-side down onto a blob of SLA resin sitting on the print bed. He tricks the printer into thinking the platform is all the way down for the first layer by interrupting the photosensor used to detect home. He lets the printer go through one layer of an STL file that contains his design, which polymerizes a thin layer of plastic onto the copper. The excess resin is wiped gently away and the board goes straight into a ferric chloride etching bath. The video below shows the whole process.

As simple as it sounds, it looks like it works really well. And [Peter] didn’t just stumble onto this method; he approached it systematically and found what works best. His tips incude using electrical tape as a spacer to lift the copper off the print surface slightly, cleaning the board with Scotchbrite rather than sandpaper, and not curing the resin after printing. His toolchain is a bit uncoventional — he used SketchUp to create the traces and exported the STL. But there are ways to convert Gerbers to STLs, so your favorite EDA package can probably fit in to the process too.

Don’t have a resin printer? Don’t worry — FDM printers can work too.

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