Keep Your Nozzle Hot And Your Prints Cool

January 29, 2016 by Gerrit Coetzee 33 Comments

Despite tuning my extruder steps perfectly, and getting good results instantly on larger prints. I was still having a ton of trouble with smaller parts. PLA is the favored printing material for its low odor, low warping, and decent material properties. It also has many downside, but it’s biggest, for the end user, lies in its large glass transition temperature range. Like all thermoplastics, it shrinks when it cools, but because of this large range, it stays expanded and, getting deep into my reserve of technical terms, bendy for a long time. If you don’t cool it, the plastic will pile up in its expanded state and deform.

The old cooling fan on my trusty and thoroughly battered Prusa i2.

I am working on a project that needs a tiny part, pictured above. The part on the left is what I was getting with my current cooling set-up and temperature settings. It had very little semblance with the CAD file that brought it into this world.

The bond between layers in a 3d print occurs when the plastic has freshly left the nozzle at its melting point. Almost immediately after that, the plastic crosses from the liquid state into a glass state, and like pressing two pieces of glass together, no further bonding occurs. This means that in order to get a strong bond between the print layers, the plastic has to have enough thermal mass to melt the plastic below it. Allowing the polymer chains to get cozy and hold hands. Nozzle geometry can help some, by providing a heat source to press and melt the two layer together, but for the most part, the fusing is done by the liquid plastic. This is why large diameter nozzles produce stronger parts.

What I’m getting at is that I like to run my nozzle temperature a little hotter than is exactly needed or even sensible. This tends to produce a better bond and sometimes helps prevent jamming (with a good extruder design). It also reduces accuracy and adds gloopiness. So, my first attempt to fix the problem was to perhaps consider the possibility that I was not 100% right in running my nozzle so hot, and I dropped the temperature as low as I could push it. This produced a more dimensionally accurate part, but a extraordinarily weak one. I experimented with a range of temperatures, but found that all but the lowest produced goopy parts.

After confirming that I could not get a significant return on quality by fine tuning my temperature, I reduced the speed of the nozzle by a large percentage. By reducing the speed I was able to produce the middle of the three printed parts shown in the opening image. Moving the nozzle very slowly gave the ambient air and my old cooling fan plenty of time to cool the part. However, what was previously a five minute part now took twenty minutes to print. A larger part would be a nightmare.

I had a little cage fan my friend had given me, and a huge one from a Mac G5 powersupply lying around. This will do. — This will do.

So, if I can’t adjust the temperature to get what I want, and I can adjust the speed; this tells me I just need to cool the part better. The glass state of the plastic is useless to me for two reasons. One, as stated before, no bonding occurs. Two, while the plastic remains expanded and bendy, the new layer being put down is being put down in the wrong place. When the plastic shrinks to its final dimension is when I want to place the next layer. Time to solve this the traditional way: overkill.

A while back my friend gifted me a little squirrel cage fan he had used with success on his 3d printer. Inspired by this, I had also scrounged a 12v, 1.7A fan from a broken Power Mac G5 power supply. When it spins up I have to be careful that it doesn’t throw itself off the table.

I should have added a rib to this bracket, this fan is heavy!

I printed out mounts for the fans. The big one got attached to the Z axis, and the little one rides behind the extruder. I fired up the gcode from before and started to print, only to find that my nozzle stopped extruding mid way. What? I soon discovered I had so much cooling that my nozzle was dropping below the 160C cold extrusion cut-off point and the firmware was stopping it from damaging itself. My heated bed also could no longer maintain a temperature higher than 59C. At this point I felt I was onto something.

I wrapped my extruder in fiberglass insulation and kapton tape, confidently turned the nozzle temperature up, set the speed to full, and clicked print. With the addition of the overkill cooling I was able to get the part shown to the right in my three example prints. This was full speed and achieved full bond. Not bad! Thus concludes this chapter in my adventures with cooling. I was really impressed by the results. Next I want to try cooling ABS as it prints. Some have reported horrible results, others pretty good ones, I’m interested. I also wonder about cooling the plastic with a liquid at a temperature just below the glass state as it is deposited. Thoughts?

3D Printer Tool: Set Your Extruder Steps With Ease

January 27, 2016 by Gerrit Coetzee 25 Comments

My printer has other issues that i'm still tuning out, but the warping in PLA and excessive surface roughness has all the signs of over extrusion. — My printer has other issues that I’m still tuning out, but the warping in PLA and excessive surface roughness has all the signs of over extrusion.

I have an old Prusa i2 that, like an old car, has been getting some major part replacements lately after many many hours of service. Recently both the extruder and the extruder motor died. The extruder died of brass fill filament sintering to the inside of the nozzle (always flush your extruder of exotic filaments). The motor died at the wires of constant flexing. Regardless, I replaced the motors and found myself with an issue; the new motor and hotend (junk motor from the junk bin, and an E3D v6, which is fantastic) worked way better and was pushing out too much filament.

The hotend, driver gear, extruder mechanics, back pressure, motor, and plastic type all work together to set how much plastic you can push through the nozzle at once. Even the speed at which the plastic is going through the nozzle can change how much friction that plastic experiences. Most of these effects are somewhat negligible. The printer does, however, have a sort of baseline steps per mm of plastic you can set.

The goal is to have a steps per mm that is exactly matched to how much plastic the printer pushes out. If you say 10mm, 10mm of filament should be eaten by the extruder. This setting is the “steps per mm” in the firmware configuration. This number should be close to perfect. Once it is, you can tune it by setting the “extrusion multiplier” setting in most slicers when you switch materials, or have environmental differences to compensate for.

This little guy lets you tune the steps per mm exactly.

The problem comes in measuring the filament that is extruded. Filament comes off a spool and is pulled through an imprecisely held nozzle in an imprecisely made extruder assembly. On top of all that, the filament twists and curves. This makes it difficult to hold against a ruler or caliper and get a trustworthy measurement.

I have come up with a little measuring device you can make with some brass tubing, sandpaper, a saw (or pipe cutter), a pencil torch, solder, and some calipers. To start with, find two pieces of tubing. The first’s ID must fit closely with the filament size you use. The second tube must allow the inside tubing to slide inside of it closely. A close fit is essential.

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3D Printing Metal From Rust

January 14, 2016 by Elliot Williams 25 Comments

It seems backwards, but engineers from Northwestern University have made 3D printing metal easier (and eventually cheaper) by adding extra production steps to the procedure. (Paper available in PDF).

Laser sintering works by laying down a thin layer of metal powder and then hitting it with a strong enough laser to sinter the particles together. (Sintering sticks the grains together without getting the metal hot enough to melt it.) The rapid local heating and cooling required to build up 3D objects expands and cools the metal, and can result in stresses inside the resulting object.

The Northwestern team still lays down layers of powder, but glues the layers together with a quick-drying polymer instead of fusing them with a laser. Once the full model is printed, they then sinter it in one piece in an oven.

anewwaytopri_tn — 3D-printed copper lattice. Credit: Ramille Shah and David Dunand

The advantages of adding this extra step are higher printing speed — squirting the liquid out of syringe heads can be faster than fusing metal particles with a laser — and increased structural integrity because the whole model is heated and cooled at one time. A fringe benefit is that the model is still a bit flexible before firing, opening up possibilities for printing a flat model and then bending it into shape before sintering.

And if that weren’t enough, the team figured that they’d add a third step to the procedure to allow it to be used with rust (iron oxide) as the starting powder. They print the rust and polymer model, then un-rust the iron using hydrogen, and then fire it as before. Why rust? Do you know anything cheaper to use as a raw material?

What do you think? The basic idea may even be DIYable — glue metal particles together and heat them up enough to stick. Not in my microwave oven, though. We’d love to see a more energy-efficient 3D metal printer.

Thanks to [Joe] for the tip!

Pewter Casting With PLA

December 27, 2015 by Al Williams 12 Comments

Over on Hackaday.io, [bms.had] is showing his technique for 3D printing molds that he uses to cast (lead-free) pewter objects. The process looks simple enough, and if you have a 3D printer, you only need some lead-free pewter, a cheap toaster oven, and PLA filament. He’s made two videos (below) that do an excellent job of showing the steps required.

Even though the pewter is hot enough to melt the PLA, it doesn’t appear to be a major problem if you quench the piece fast enough. According to [bms.had], a slower quench will melt some PLA although that creates a smoother surface. You can see the 0.31 mm layer lines in the cast, though, although you can use any layer height you like to control that. Creating the mold is simple (the videos use Tinkercad, although anything suitable for creating 3D models would work). You essentially attach a funnel to your part and make the entire part a hole inside an enveloping shape.

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3D Printed Hydraulics

December 20, 2015 by Al Williams 37 Comments

[Robert MacCurdy] at MIT wants to change how people think about hydraulics. Using fluid can be very useful in systems like robots, but it is often the case that the tubing that carries hydraulic fluid is not an integrated part of the overall design. [MacCurdy] and his colleagues have modified a 3D printer to allow it directly include hydraulic components as it prints.

The idea is simple. The team started with a printer that uses a liquid ink that is UV cured to produce solid layers. The printer has the ability to use multiple liquids, and [MacCurdy] uses hydraulic fluid (that does not UV cure) as one of the print materials. Just as you can use a 3D printer to build structures within other structures, printing the hydraulics allows for complex closed systems that use the UV-cured resin as mechanical parts that can transfer pressure to and from the hydraulic system.

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Mains Powered 3D Printer Heated Beds

December 16, 2015 by Brian Benchoff 160 Comments

Converting mains voltage down to 12 or 24VDC to drive a heating element makes no sense. To get 120 watts at 12 volts requires thick wires that can handle 10 amps, whereas at 120V, tiny 1A wires will do. If you’ve ever felt the MOSFET that switches your heated bed on and off, you know it’s working hard to pass that much current. [Makertum] is of the opinion this is a dumb idea. He’s creating a 110 / 230 V, mains-powered heated bed.

Creating a PCB heat bed isn’t an art – it’s a science. There are equations and variables to calculate, possibly some empirical measurements by measuring the resistance of a trace, but Ohm’s Law is a law for a reason. If you do things right, you can make a PCB heat bed perfectly suited for the task. You can even design in safety features like overcurrent protection and fuses. It can’t be that hard. After all, your house is full of devices that are plugged into the wall.

However, there’s a reason we use 12V and 24V heated beds – they give us, at the very least, the illusion of safety. Therefore, [Makertum] is looking for a few comments from specialists and people who know what they’re doing.

Although a mains powered heated bed sounds scary for a hobbyist-built 3D printer, there are a number of positives to the design. It would heat up faster, thin down a few parts, and significantly reduce the overall cost of the printer by not requiring another 100 Watts delivered from a 12V power supply. It’s a great idea if it doesn’t burn down the house. Anyone want to help?

3D-Printing The Most Ornate Room

December 12, 2015 by Elliot Williams 21 Comments

It’s no secret that we like 3D printing, but Artist and architect [Michael Hansmeyer] really likes 3D printing. So much so that he’s based his entire career around exploring the artistic possibilities of what he calls “computational architecture”.

We first fell in love with [Michael]’s work “Columns” because it was both daring and relatively low-budget at the same time. He made a series of architectural-sized columns out of cross-sections of laser-cut cardboard. Why cardboard? Because his goal was to make the columns as complex as possible and the current range of 3D printers couldn’t give him the resolution he wanted.

Fast-forward to “Digital Grotesque”. Now [Michael] has access to a large-scale sand printer, and the license to go entirely nuts. He makes a space reminiscent of a Rococo grotto, but full of so much detail that you can’t really take it all in: it’s nearly fractal. Some stats: 11 tons of printed sandstone, 260 million surfaces, 30 billion voxels. We’re stoked that we don’t have to dust it!

His latest piece, “Arabesque Wall” is partly organic and elegant, and part Aliens. If we can play art critic, we think it’s beautiful. Go click through the portfolio. (And although they never got printed, we really like some of the “Voxels” series of cellular-automata pieces.)

From new paint materials opening up new color possibilities to new instruments enabling entirely different types of music, art, and technology mutually inform each other much more than we often appreciate. In ten years time, we’ll be looking back on this work and saying “this piece looks good” and “that piece looks bad” instead of “wow, amazing tech!”. But for now, we’re also content to wallow in the “wow”.