Restarting 3D Prints

Image of a 3D print which was restarted using a different material

If a 3D printer is interrupted during a print, it will usually result in a junk part. Resuming the print can be very difficult. A group of researchers at MIT have built an add-on for 3D printers that uses a laser scanner to evaluate the state of the print, and allows the printer to restart.

While this will allow you to salvage some partially competed prints, the interesting application is switching between materials. In the image above, the lower piece was printed in ABS. The print was interrupted to change materials, and the top cube was printed in PLA. This allows for prints to mix materials and colors.

The add-on was tested with the Solidoodle 3D printer, and can be built for about $60. It requires a laser mounted to the print head, and a low-cost webcam for performing the measurements. While the group will not be continuing work on this project, they plan to open source their work so others can continue where they’ve left off.

After the break, we have a video of the printer performing a scan and resuming a print.

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Programmable Logic I – PLA/PAL


Yeah I am still a little pissed that the competition is still around and we aren’t, and by “we” I mean Commodore Business Machines (CBM). It was Commodore that had the most popular home computer ever in the C64 (27 Million) and it was a team of MOS engineers after all, that had the idea to make a “micro” processor out of a 12 square inch PCB.

MOS Technologies logo and address
MOS Technology in King of Prussia/Norristown

Of course they did work at Motorola at the time and “Mot” did not want anything to do with a reduction of the profit margin on the pie-plate size processor. Of course MOS got sued by Motorola but that was an average Tuesday at MOS/CBM. I absolutely credit CBM with buying the MOS Technologies chip foundry, as together we could make our own processors, graphics chips, sound chips, memory controllers, and programmable logic.

With this arsenal at our call we didn’t have to make compromises the way other companies did such as conforming to the bus spec of an industrial standard 6845 or having to add extra logic when a custom extra pin would work. We could also make sprites.

6502 Design Team
6502 Design Team (EE Times 1975,

The compromise we did have to make when designing was cost, and I mean the kind of cost reduction where finding a way to save a dollar ($1USD) saved millions in the production run. I knocked $.90USD out of a transformer one day and I couldn’t focus the rest of the day due to elation.

Cost reduction is a harsh mistress however as you can’t just do it a little some of the time or only when you want to. The mental exercise of multiplying anything times a million was always there, it made it hard to buy lunch — I’d be blocking the lunch line while figuring the cost of a million tuna sandwiches FOB Tokyo Continue reading “Programmable Logic I – PLA/PAL”

Recycling Plastic With Liquid Nitrogen


Recycling 3D printer filament isn’t a new idea, and in fact there are quite a few devices out there that will take chunks ABS, PLA, or just about any other thermoplastic and turn them into printer filament. The problem comes when someone mentions recycling plastic parts and turning them into filament ready to be used again. Plastics can only be recycled so many times, and there’s also the problem of grinding up your octopodes and companion cubes into something a filament extruder will accept.

The solution, it appears, is to freeze the plastic parts to be recycled before grinding them up. Chopping up plastic parts at room temperature imparts a lot of energy into the plastic before breaking. Freezing the parts to below their brittle transition temperature means the resulting chips will have clean cuts, something much more amenable to the mechanics of filament extruders.

The setup for this experiment consisted of cooling PLA plastic with liquid nitrogen and putting the frozen parts in a cheap, As Seen On TV blender. The resulting chips were smaller than the plastic pellets found in injection molding manufacturing plants, but will feed into the extruder well enough.

Liquid nitrogen might be overkill in this case; the goal is to cool the plastic down below its brittle transition temperature, which for most plastics is about -40° (420° R). Dry ice will do the job just as well, and is also available at most Walmarts.


3D Printed Velcro


With new materials comes new possibilities in fabrication, and with 3D printers, this observation is no different. In the past year or so, there have been a few very interesting new filaments that have come into mainstream use – a printable sandstone, high impact polystyrene, and a flexible PLA. When [Rich] saw a bike light that had an integrated hook-and-loop fastener – think Velcro – built in to its enclosure, he thought to himself, ‘I could do that too.’

[Rich]’s “ElastoStraps” are printed with Makergeek’s Flexible PLA, and the entire device works surprisingly similar to other hook and loop fasteners with a registered trademark. The design is up on Thingiverse, and since the object was designed with OpenSCAD, the 3D printed Velcro can also be opened up in the Customizer for hook-and-loop straps that perfectly suit your needs.

3D Printering: Alternative Filaments


ABS and PLA are the backbones of the 3D printing world. They’re both easy to obtain and are good enough for most applications. They are not, however, the be-all, end-all filaments for all your 3D printing needs. Depending on your design, you may need something that is much tougher, much more flexible, or simply has a different appearance or texture. Here are a few alternative plastics for your RepRap, Makerbot, or other 3D printer:

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Smoothing PLA printed parts

We’ve seen a few advances in the finishing processes of 3D prints over the last few months that result in some very attractive parts that look like they were injection molded. Smoothing ABS prints is now a necessary skill for anyone looking to produce professional parts, but those of us using PLA for our RepRaps have been left in the cold. After some experimentation, the guys over at protoparadigm have come up with a way to smooth out those PLA prints, using the same technique and a chemical that’s just as safe as acetone.

Instead of acetone, the guys at protoparadigm are using tetrahydrofuran, or THF, as a solvent for PLA. Other PLA solvents aren’t friendly to living organisms or are somewhat hard to obtain. THF has neither of these qualities; you still need to use it in a well ventilated area with nitrile gloves, but the same precautions when using acetone or MEK still apply. It’s also easy to obtain, as well: you can grab some on Amazon, even.

The process for smoothing PLA prints with THF is the same as smoothing ABS prints with acetone. Just suspend the print in a glass container, pour in a tiny amount of the solvent, and (gently) heat it. The evaporated solvent will smooth all the ridges out of the print, leaving a shiny and smooth surface. You can, of course, hand polish it by dedicating a lint-free cloth and a pair of gloves to the task.

Hot plate stirrer dissolves support material in 3D printed objects


When you want to print a 3D object you run into problems if there is a part that has nothing below it. The hot, soft filament coming out of the extruder will droop with gravity if not given something to rest on while it hardens. The solution is to use a second material as a support. But then you’ve got to find a way to remove the support structure when the printing is done. That’s where this beauty comes in. It’s a heated stir plate for dissolving PLA.

The PLA is printed using a second extruder head. Once the part is cooled [Petrus] puts it into a heated bath of sodium hydroxide (lye). The solvent will remove the PLA but not harm the ABS. Speaking of ABS, [Petrus] also mentions that this can double as a temperature controlled hot plate for polishing ABS prints using acetone vapor.

There’s all kinds of good stuff inside of this beast so do check out the full plans to learn more. Our favorite part is the stir bar which is a piece of threaded rod and a couple of nuts. To make it safe to submerge in the chemicals he 3D printed a pill-shaped enclosure for it.

[Thanks Matt]