There’s A Wrinkle In This 3D Printed Wankel

February 10, 2022 by Matthew Carlson 10 Comments

Rotary engines such as the Wankel have strange shapes that can be difficult to machine (as evidenced by the specialized production machines and patents in the 70s), which means it lends itself well to be 3D printed. The downside is that the tolerances, like most engines, are pretty tight, and it is difficult for a printer to match them. Not to be dissuaded, [3DprintedLife] designed and built a 3D printed liquid piston rotary engine. The liquid piston engine is not a Wankel and is more akin to an inside-out Wankel. The seals are on the housing, not the rotor itself, and there are three “chambers” instead of two.

The first of many iterations didn’t run. There was too much friction, but there were some positive signs as pressure was trapped in a chamber and released as it turned. The iterations continued, impressively not using any o-rings to seal, but instead sanding each part down using a 1-2-3 block as a flat reference, within 25 microns of the design. Despite his care and attention to detail, it still couldn’t self-sustain. He theorizes that it could be due to the resin being softer than other materials he has used in the past. Not to be left empty-handed, he built a dynamo to test his new engine out. It was a load cell and an encoder to measure speed and force. His encoder had trouble keeping up, so he ordered some optical limit switches.

This engine is a follow-on to an earlier 3D printed air-powered Wankel rotary engine, and we’re looking forward to part two of the liquid piston series. Video after the break.

Continue reading “There’s A Wrinkle In This 3D Printed Wankel” →

3D Printer Showdown: $350 Consumer Vs $73,000 Pro Machine

January 29, 2022 by Al Williams 35 Comments

The quality of consumer-grade 3D printing has gone way up in recent years. Resin printers, in particular, can produce amazing results and they get less expensive every day. [Squidmar] took a miniature design and printed it (or had it printed) on some cheap resin printers and a 65,000 Euro DWS029. How much difference could there be? You can see for yourself in the video below.

We were surprised at the specs for the more expensive machine. It does use a solid-state laser, but for that cost, the build volume is relatively small — around 15 x 15 x 10 cm. There were actually five prints created on four printers. Three were on what we think of as normal printers, one was on the 65,000 Euro machine, and the fifth print was on a 10,000 Euro printer that didn’t look much different from the less expensive ones.

Of course, there is more to the process than just the printer. The resin you use also impacts the final object. The printers tested included a Phrozen 4K Mini, a Phrozen 8K Mini, a Solos Pro, and the DWS 029D. The exact resins or materials used was hard to tell in each case, so that may have something to do with the comparisons, too.

Do you get what you pay for? Hard to say. The 8K and Solos were neck-and-neck with some features better on one printer and some better on the other. The DWS029D did perform better, but was it really worth the increase in price? Guess it depends on your sensitivity. The 8K printer did a very credible job for a fraction of the cost. Of course, some of that could have been a result of the materials used, too, but it does seem likely that a very expensive dental printer ought to do better than a hobby-grade machine. But it doesn’t seem to do much better.

The DWS printer uses a laser, while most hobby printers use UV light with an LCD mask. We’ve seen low-end resin printers on closeout for around $100 and you can get something pretty nice in the $200 neighborhood. In between these two extremes are printers that use Digital Light Processing (DLP).

Continue reading “3D Printer Showdown: $350 Consumer Vs $73,000 Pro Machine” →

Fail Of The Week: 3D Printed Parts That Burn Like NASA’s Rocket Fuel

January 9, 2022 by Dave Rowntree 21 Comments

[Integza] is on a mission to find as many ways as possible to build rockets and other engines using 3D printing and other accessible manufacturing techniques. He had an a great idea – is it possible to 3D print a solid fuelled rocket, (video, embedded below) specifically can you 3D print the rocket grain itself? By using the resin as a fuel and mixing in a potent oxidiser (ammonium perchlorate specifically – thanks for the tip NASA!) he has some, erm, mixed success.

Effective thrust vs grain cross-sectional profile

As many of us (ahem, I mean you) can attest to, when in the throes of amateur solid-propellant rocket engine experimentation (just speaking theoretically, you understand) it’s not an easy task to balance the thrust over time and keep the combustion pressure within bounds of the enclosure’s capability. Once you’ve cracked making and securing a nozzle within the combustion chamber, the easiest task is to get control of the fuel/oxidiser/binder (called the fuel grain) ratio, particle size and cast the mixture into a solid, dry mass inside. The hard part is designing and controlling the shape of the grain, such that as the surface of the grain burns, the actively burning surface area remains pretty constant over time. A simple cylindrical hole would obviously increase in diameter over time, increasing the burning surface area, and causing the burn rate and resulting pressure to constantly increase. This is bad news. Various internal profiles have been tested, but most common these days is a multi-pointed star shape, which when used with inhibitor compounds mixed in the grain, allows the thrust to be accurately controlled.

[Integza] tried a few experiments to determine the most appropriate fuel/binder/oxidiser ratio, then 3D printed a few fuel grain pellets, rammed them into an acrylic tube combustion chamber (obviously) and attached a 3D printed nozzle. You can see for yourself the mach diamonds in the exhaust plume (which is nice) due to the supersonic flow being marginally over-expanded. Ideally the nozzle wouldn’t be made from plastic, but it only needs to survive a couple of seconds, so that’s not really an issue here.

The question of whether 3D printed fuel grains are viable was posed on space stack exchange a few years ago, which was an interesting read.

We’ve seen some more sophisticated 3D printed rocket engines lately, such as this vortex-cooled, liquid-fuel engine, and over on Hackaday,IO, here’s a 3D printed engine attempting to use PLA as the fuel source.

Continue reading “Fail Of The Week: 3D Printed Parts That Burn Like NASA’s Rocket Fuel” →

Continuous Resin Printer Shows The Speed

September 16, 2021 by Dave Rowntree 11 Comments

Redditor [No-Championship-8520] aka [Eric Potempa] has come up with an interesting DIY take on the Continuous Liquid Interface Production (CLIP) process currently owned and developed by Carbon Inc.

The usual resin 3D printer you may be familiar with is quite a simple machine. The machine has only one axis, which is the vertically moving build platform. A light exposes a photosensitive resin that cures on and is then pulled up off of a transparent window, before the next layer is exposed.

CLIP is a continuous resin printing process that speeds up printing by removing this peeling process. It utilises a bottom membrane that is permeable to oxygen. This tiny amount of oxygen right at the boundary prevents the solidified resin from sticking to the bottom, allowing the Z axis to be moved up continuously, speeding up printing significantly.

The method [Eric] is using is based around a continuously rotating bath to keep the resin moving, replenishing the resin in the active polymerisation zone. The bottom of the bath is made from a rigid PDMS surface, which is continuously wiped with a squeegee to replenish the oxygen layer. He notes the issues Carbon are still having with getting enough oxygen into the build layer, which he reckons is why they only show prints of smaller or latticed structures. His method should fix that issue. The build platform is moved up slowly, with the part appearing in one long, continuous movement. He reports the printing speed as 280 mm/hour which is quite rapid to say the least. More details are very scarce, and the embedded video a little unclear, but as one commentator said “I think we just saw resin printing evolve!” the next snarky comment changed the “evolve” to “revolve” which made us giggle.

Now, we all know that 3D printing is not at all new, and only the expiration of patents and the timely work by [Adrian Bowyer] and the reprap team kickstarted the current explosion of FDM printers. Resin printers will likely be hampered by the same issues until something completely new kickstarts the next evolution. Maybe this is that evolution? We really hope that [Eric] decides to write up his project with some details, and we will be sitting tight waiting to pore over all the gory details. Fingers crossed!

New Part Day: DLP300s The Next Big Thing For Low Cost Resin Printing?

September 1, 2021 by Dave Rowntree 73 Comments

The majority of non-SLA resin 3D printers, certainly at the hacker end of the market, are most certainly LCD based. The SLA kind, where a ultraviolet laser is scanner via galvanometers over the build surface, we shall consider no further in this article.

What we’re talking about are the machines that shine a bright ultraviolet light source directly through a (hopefully monochrome) LCD panel with a 2, 4 or even 8k pixel count. The LCD pixels mask off the areas of the resin that do not need to be polymerised, thus forming the layer being processed. This technique is cheap and repeatable, hence its proliferance at this end of the market.

They do suffer from a few drawbacks however. Firstly, optical convergence in the panel causes a degree of smearing at the resin interface, which reduces effective resolution somewhat. The second issue is one of thermal control – the LCD will transmit less than 5% of the incident light, so for a given exposure at the resin, the input light intensity needs to be quite high, and this loss in the LCD results in significant internal heating and a need for active cooling. Finally, the heating in the LCD combined with intense UV radiation degrades the LCD over time, making the LCD itself a consumable item.

Continue reading “New Part Day: DLP300s The Next Big Thing For Low Cost Resin Printing?” →

Off-The-Shelf Parts Make A Tidy Heater For Resin Printer

April 1, 2021 by Lewin Day 6 Comments

Resin printers can offer excellent surface finish and higher detail than other 3D printing technologies, but they come with their own set of drawbacks. One is that they’re quite sensitive to temperature, generally requiring the resin chamber to be heated to 25-30 degrees Celsius for good performance. To help maintain a stable temperature without a lot of mucking around, [Grant] put together a simple chamber heater for his printer at home.

Rather than go for a custom build from scratch with a microcontroller, [Grant] was well aware that off-the-shelf solutions could easily do the job. Thus, a W1209 temperature control board was selected, available for under $5 online. Hooked up to a thermocouple, it can switch heating elements via its onboard relay to maintain the set temperature desired. In this case, [Grant] chose a set of positive-temperature coefficient heating elements to do the job, installing them around the resin chamber for efficiency.

The heater can preheat the chamber in under fifteen minutes, much quicker than other solutions using space heaters or heat mats. The time savings will be much appreciated by [Grant], we’re sure, along with the attendant increase in print quality. If you’re still not sure if resin printing is for you, have a read of our primer. And, if you’ve got your own workflow improvements for resin printing, drop us a line!

Building A UV Curing Station For Resin Prints

September 5, 2020 by Lewin Day 10 Comments

Resin printers have a lot going for them – particularly in regards to quality surface finishes and excellent reproduction of fine details. However, the vast majority rely on UV light to cure prints. [douwe1230] had been using a resin printer for a while, and grew tired of having to wait for sunny days to cure parts outside. Thus, it was time to build a compact UV curing station to get the job done.

The build consists of a series of laser-cut panels, assembled into a box one would presume is large enough to match the build volume of [douwe1230’s] printer. UV LED strips are installed in the corners to provide plenty of light, and acrylic mirrors are placed on all the walls. The use of mirrors is key to evenly lighting the parts, helping to reduce the likelihood of any shadows or dead spots stopping part of the print from curing completely. In the base, a motor is installed with a turntable to slowly spin the part during curing.

[Douwe1230] notes that parts take around about 10 minutes to cure with this setup, and recommends a flip halfway through to make sure the part is cured nice and evenly. We’ve seen other similar DIY builds too, like this one created out of a device aimed at nail salons. If you’re struggling with curing outside, with the weather starting to turn, this might just be the time to get building!