How Thermal Post-Curing Resin Prints Affects Their Strength

March 10, 2024 by Maya Posch 6 Comments

Tensile strength of resin parts. (Credit: CNC Kitchen) — Credit: CNC Kitchen

Resin 3D prints have a reputation for being brittle, but [Stefan] over at [CNC Kitchen] would like to dispel this myth with the thing which we all love: colorful bar graphs backed up by scientifically appropriate experiments. As he rightfully points out, the average resin printer user will just cure a print by putting it in the sunshine or in a curing station that rotates the part in front of some UV lights. This theoretically should cause these photosensitive resins to fully cure, but as the referenced Formlabs documentation and their Form Cure station indicate, there’s definitely a thermal element to it as well.

To test the impact of temperature during the UV curing process, the test parts were put into an oven along with the UV lamp. Following this uncured, ambient cured and parts cured at 40 to 80 ºC were exposed to both tensile strength tests as well as impact strength. The best results came from the Siraya Tech Blu resin cured at 80 ºC, with it even giving FDM-printed parts a run for their money, as the following graphs make clear. This shows the value of thermal post-curing, as it anneals the resin prints. This reduces their impact strength somewhat, but massively improves their tensile strength.

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High Temp Resin Means Faster Hot Foil Stamping

September 23, 2023 by Kristina Panos 8 Comments

[This Designed That] does a lot of hot foil stamping. That’s the shiny embellishment you’ll see on wedding invitations and your fancier letterheads. They wanted a way to quickly see if the process is right for a given design, and how it might come together if so. Many of the designs involve letter forms, which they have tried milling out of brass in the past, but the process is fiddly and takes a while. Seeking a faster way to test designs, [This Designed That] turned to 3D printing.

They achieved good results with an Elegoo Mars Pro, but the the most important thing here is the resin needs to withstand at least 130 C, which is the max that [This Deigned That] usually runs it at. The answer was in Phrozen TR300 resin, which can handle temps up to 160 C.

In trials, the stamp heat measured roughly 30 C lower on average than the press, so [This Designed That] kept turning up the heat, but it just wasn’t conductive enough. So they started experimenting with ways to increase heat transfer. First they tried molding metal powder, but it didn’t work. After briefly flirting with electroplating them, [This Designed That] finally tried some aluminum tape, wrapped tight and burnished to the design.

Now the hot foil machine stamps perfectly at only 120 C — the lower end of the standard temperature that [This Designed That] typically runs the thing. They are chuffed at the results, and frankly, so are we. Be sure to check out the process video after the break.

Curious about hot foil stamping machines? Check out this retrofit job.

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Hackaday Prize 2023: Ubo Project: Building For Builders

August 24, 2023 by Dave Rowntree 6 Comments

The Ubo Pod by [Mehrdad Majzoobi] is a very highly polished extension pack and enclosure for the Raspberry Pi 4, which shows you how far you can go to turn a bare PCB into something that rivals the hardware offerings from Google and others. Gadgets like the Sonos speakers and Amazon or Google’s covert listening devices (aka Echo, Alexa, or whatever they’re branded as) are fun to play with. Still, the difficulty of hacking custom applications into them and god-forbid adding one’s own extension hardware, makes them fairly closed ecosystems. Add in the concerns of privacy and data security; they look less and less attractive the closer you look. Luckily the Raspberry Pi and its friends have improved the accessibility to the point where it’s positively easy to create whatever you want with whatever hardware you need, and to that end we think [Mehrdad] has done a splendid job.

The custom top PCB sits below the wooden top surface, hosting a central LCD display with push buttons located around it. Also sitting atop are some IR transmitters and receivers as well as RGB LEDs for the ring lighting. This top PCB acts as a RPi hat, and plugs into an RPi4 below, which then attaches to a side board via some PCB-mounted connectors, matching up with the USB and audio connectors. This board seems to act purely as an interconnect and form-factor adaptor allowing interfaces to be presented more conveniently without needing wires. This makes for a very clean construction. Extensive use of resin printing is shown, with lots of nice details of how to solve problems such as LED diffusion and bleeding. Overall, a very slick and well-executed project, that is giving us a few ideas for our own projects.

This type of project is commonplace on these fair pages, like this DIY smart speaker for example. With the supply of pi being still a little difficult to deal with, could you roll your own or get an alternative? What about just using your old mobile phone?

Holograms: The Future Of Speedy Nanoscale 3D Printing?

April 9, 2023 by Dave Rowntree 7 Comments

3D printing by painting with light beams on a vat of liquid plastic was once the stuff of science fiction, but now is very much science-fact. More than that, it’s consumer-level technology that we’re almost at the point of being blasé about. Scientists and engineers the world over have been quietly beavering away in their labs on the new hotness, nanoscale 3D printing with varying success. Recently IEESpectrum reports some promising work using holographic imaging to generate nanoscale structures at record speed.

Current stereolithography printers make use of UV laser scanned over the bottom of a vat of UV-sensitive liquid photopolymer resin, which is chemically tweaked to make it sensitive to the UV frequency photons. This is all fine, but as we know, this method is slow and can be of limited resolution, and has been largely superseded by LCD technology. Recent research has focussed on two-photon lithography, which uses a resin that is largely transparent to the wavelength of light concerned, but critically, can be polymerized with enough energy density (i.e. the method requires multiple photons to be simultaneously absorbed.) This is achieved by using pulsed-mode lasers to focus to a very tight point, giving the required huge energy density. This tight focus, plus the ability to pass the beam through the vat of liquid allows much tighter image resolution. But it is slow, painfully slow.

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The Best Threaded Holes For Resin Parts

November 1, 2022 by Danie Conradie 21 Comments

Threaded inserts are great for melting into FDM prints with a soldering iron. The process isn’t so simple for resin prints, since they don’t generally soften with heat. Off course, you can also print the threads directly, screw a bolt into an un-threaded hole, or tap a hole. Following his usual rigorous testing process, [Stefan] from CNC Kitchen investigated various ways of adding threaded holes to resin prints.

After establishing a pull-out force on PLA using threaded inserts (205 kg) and tapped holes (163 kg), [Stefan] tested parts printed with Prusament Tough Anthracite resin. Un-threaded and tapped holes failed at 44 kg and 55 kg respectively, while printed threads were almost twice as strong, reaching 106 kg before breaking. Stephan also tried gluing inserts into the parts using resin and CA glue. The resin didn’t cure properly in the opaque parts (6 kg) while CA was comparable to plastic threads, failing at 52 kg.

Chart of results — TLDR: Print your threads for best results

[Stefan] also tested regular ELEGOO Translucent resin. The higher hardness of the cured resin allowed the parts to hold on to around 100 kg for un-threaded and tapped holes, while printed threads reached 120 kg. Threaded insert glued with resin did better on the transparent parts thanks to improved UV penetration, but were very inconsistent. Inserts glued with CA performed about the same as on the Prusament parts, failing at 56 kg.

In an attempt to improve the performance of the inserts [Stefan] printed some parts with stepped holes to match the geometry of the inserts, which had the advantage of preventing the insert from falling through during gluing. It only made a marginal difference on the Prusament parts but boosted the strength of CA-glued inserts on the ELEGOO resin to 82 kg. Two-part epoxy was also tried, which matched the un-threaded holes in strength.

So for resin parts you’ll probably be best served by just modeling the threads in CAD and printing them directly. If you need to be able to repeatedly screw and unscrew fasteners in a hole without stripping, threaded holes with CA or epoxy might be a better solution.

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resin printed pulsejet engine in operation

A Detonation Engine Prototyped Using Resin Printing

August 29, 2022 by Dave Rowntree 5 Comments

Over the years [Integza] has blown up or melted many types of jet engine, including the humble pulsejet. Earlier improvements revolved around pumping in more fuel, or forced air intakes, but now it’s time for a bit more refinement of the idea, and he takes a sidestep towards the more controllable detonation engine. His latest experiment (video, embedded below) attempts to dial-in the concept a little more. First he built a prototype from a set of resin printed parts, with associated tubing and gas control valves, and a long acrylic tube to send the exhaust down. Control of the butane and air injection, as well as triggering of the spark-ignition, are handled by an Arduino — although he could have just used a 555 timer — driving a few solid state relays. This provided some repeatable control of the pulse rate. This is a journey towards a very interesting engine design, known as the rotating detonation engine. This will be very interesting to see, if he can get it to work.

supersonic exhaust plume from a pulsejet engine — Supersonic exhaust plume with the characteristic ‘mushroom’ shape

Detonation engines operate due to the pressure part of the general thrust equation, where the action is in the detonative combustion. Detonative combustion takes place at constant pressure, which theoretically should lead to a greater efficiency than boring old deflagration, but the risks are somewhat higher. Apparently this is tricky to achieve with a fuel/air mix, as there just isn’t enough oomph in the mixture. [Integza] did try adding a Shchelkin spiral (we call them springs around here) which acts to slow down the combustion and shorten the time taken for it to transition from deflagration to detonation.

It sort of worked, but not well enough, so running with butane and pure oxygen was the way forward. This proved the basic idea worked, and the final step was to rebuild the whole thing in metal, with CNC machined end plates and some box section clamped with a few bolts. This appeared to work reasonably well at around 10 pulses/sec with some measurable thrust, but not a lot. More work to be done we think.

We hinted at earlier work on forced-air pulsejets, so here that is. Of course, whilst we’re on the subject of pulsejets, we can’t not mention [Colinfurze] and his pulsejet go kart.

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Transparent Cylinder Shows You What You Otto Know About 4 Cycle Engines

July 20, 2022 by Ryan Flowers 15 Comments

When we think of a typical four stroke internal combustion engine, we think of metal. And for any type of longevity or performance, that’s certainly the right choice. But [Integza] wanted to see what happens inside a 4 stroke engine, and it wasn’t enough to see it from a transparent cylinder head. No, he wanted to see it in the cylinder itself. Thanks to advances in material sciences, he got his wish as seen in the video below the break.

While researching possible transparent materials to use as a cylinder on his model engine, he learned about resin polishing. Combining his newly learned resin polishing knowledge with his knowledge of 3D printing, [Integza] printed a new cylinder and polished the resin until it was transparent. The engine ran, but misfired terribly.

The experiment progressed into trying different fuels and learning the differences between them, as well as uncovering a new-to-him mystery: Why was the engine misfiring, and why did the different fuels act so dramatically different? Indeed, more learning and more experimenting is needed. But if you want to see the great sight of watching combustion take place in slo-mo, you have to check out the video below.

3D printing has come a long way in a short time, and may even hold the key to practical scramjets for hypersonic aircraft.

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