After going through all the trouble of printing a part in resin, discovering it feels sticky or tacky to the touch is pretty unwelcome. Giving the model some extra ultraviolet (UV) curing seems like it should fix the problem, but it probably does not. So, what can be done?
The best thing to do with a sticky print is to immediately re-wash it in clean isopropyl alcohol (IPA) before the UV present in ambient light cures stray resin. If the part remains sticky after it is dry, more aggressive steps can be taken.
Adding a resin printer to one’s workbench has never looked so attractive, nor been so affordable. Complex shapes with effortlessly great detail and surface finish? Yes, please! Well, photos make the results look effortless, anyway. Since filament-based printers using fused deposition modeling (FDM) get solid “could be better” ratings when it comes to surface finish and small detail resolution, will a trusty FDM printer end up retired if one buys a resin printer?
The short answer is this: for users who already use FDM, a resin-based stereolithography (SLA) printer is not likely to take over. What is more likely to happen is that the filament printer continues to do the same jobs it is good at, while the resin printer opens some wonderful new doors. This is partly because those great SLA prints will come at a cost that may not always justify the extra work.
Let’s go through what makes SLA good, what it needs in return, and how it does and doesn’t fit in with FDM.
When SLA Is Good, It’s REALLY Good
The sweet spot for resin printing is this: small objects with smooth finishes, organic curves, and surface details. With SLA, these objects print more reliably and at a consistently higher quality than with FDM — as long as the operator does a good job with layout and support placement, anyway.
A big reason for this is that SLA does not produce layer lines the way FDM does. FDM prints are notorious for visible layer lines, and those lines are at their worst when spread across curved surfaces. SLA still creates objects one layer at a time, but the process doesn’t leave obvious lines.
There is also more freedom in part orientation when printing in resin. Unlike FDM, resin prints are isotropic. In the context of 3D printing, this means that the printed object’s physical properties do not change with respect to physical orientation. As long as a part is supported enough to print properly, a resin printer doesn’t much care in which orientation or at what angle it builds an object; the result will come out the same. This gives SLA printers more flexibility when it comes to part orientation, which helps when trying to keep presentation surfaces and details free from supports.
Niche Applications for SLA’s Strengths
One example of a niche for what resin printing is good at is gaming miniatures and figures. Tabletop enthusiasts are buying printers and resin, and designers of gaming-related models are finding success as well. The more successful ones thrive on sites like Patreon, with thousands of monthly supporters.
Engineering applications can have a place with SLA, so long as the objects are small enough. The build volume of most SLA printers is revoltingly tiny compared to FDM, but they make up for it with the ability to handle shapes and details that FDM would have problems with.
Beware SLA’s Added Costs
SLA printing brings some annoying buddies everywhere it goes in the form of added costs. These aren’t costs for the machines themselves; hobbyist SLA printers are very affordable. These ongoing costs are for consumables, increased time for upkeep and part processing, and storage space.
SLA requires more setup and cleanup than FDM. Printed parts need to be washed (usually in an alcohol bath) after printing, and possibly post-cured with additional UV exposure. Since resin is messy, disposable gloves and a spill-resistant work area are required. Another thing to consider is that resin isn’t meant to be left sitting in a printer for long periods, so when printing is done for the forseeable future, it’s time to empty the printer and clean the parts.
All of this takes time, but it also takes up valuable space in a work area. Bottles of resin, containers of alcohol, wash bins, gloves, a drip-proof work space, all of it takes up storage and table space. SLA printing as a whole will take up far more room than just the printer itself.
The other thing to consider is the need for manual post-processing. Resin prints tend to require a lot of supports, and those supports need to be removed by hand. These leave behind small marks that may need to be sanded away. With FDM, supports are a last resort that are used only if needed, but with SLA they are the rule rather than the exception.
Things FDM Is Still Good At
A well-maintained FDM printer is a fantastic tool for prototyping, iterating on designs, and creating functional parts. FDM also has other advantages that really stand out when contrasted with resin printing.
FDM is perfectly happy to wait patiently until needed, at which point a print can be started with a minimum of fuss. The consumables are few and reasonably priced. Filament is best stored in a dry environment, but besides that, it doesn’t ask for much. Swapping filament types or colors is simple, clean, and easy. Even a failed print doesn’t usually involve much more than sweeping away a mess of plastic and trying again.
The biggest disadvantages are related to layer line visibility, the resolution of surface detail, and working with curved organic shapes. None of these can be waved away, but they can be mitigated to some extent. Variable Layer Height tries to address layer line visibility, and it is a feature that has worked its way into most slicer software. The ability to render very small details and features can be improved, to some extent, by swapping a printer’s standard 0.4 mm nozzle for a smaller one.
FDM printers are most challenged by being asked to print curved objects that have no flat areas and no real “up” or “down”. One option is splitting these objects into smaller and more easily-printed ones, but that’s not always practical. Printing a tricky model will require supports, and supports with FDM always result in degraded surface quality. Water-soluble support structures can help mitigate this, but doing so requires multi-material printing. SLA, on the other hand, is far more suited to such objects.
Is There Room for Both?
Resin prints look fantastic and it may be tempting to think of SLA as superior to FDM, but that is not the whole story. They are different tools, and good at different things. Unless your needs are very specific, you’ll probably benefit from access to both.
If you need to print small objects with good surface finish and detail resolution, and you can deal with the added hassles of working with resin, then SLA is definitely for you. But even if you only print small objects, a working FDM printer can easily earn its place on your workbench with the ability to create functional parts without any significant setup and cleanup. If you’re considering an SLA printer, don’t plan to ditch FDM just yet.
I regularly use both but personally, I always choose a filament-based printer if possible; even if a final model will eventually be printed in resin, it’s simply cheaper and faster and easier to prototype and iterate with FDM.
If you have access to both, has this also been your experience? Do you know of a niche for resin printing that hits the spot in a way nothing else does, the way SLA has done with tabletop enthusiasts? We want to hear all about it, so let us know in the comments.
Nowadays, resin printers are highly accessible and can do some great stuff. But between isopropyl alcohol for part rinsing and the fact that some resins have a definite smell to them, ventilation can get important fast. The manufacturers don’t talk much about this part of the resin printing experience, but it’s there nevertheless. So what can be done when smells become a problem?
I recently had to deal with this when I printed several liters of resin worth of parts. That’s a lot of resin, and a lot of alcohol for part washing. Smells — which had never been much of a problem in my work area — suddenly became an issue.
Flexible steel sheets as the foundation for build platforms are used to great advantage in FDM 3D printers. These coated sheets are held flat by magnets during printing, and after printing is done the sheet (with print attached) can be removed and flexed to pop the prints free. This got [Jan Mrázek] thinking. He was pretty sure the concept could extend to the build platform on his Elegoo Mars resin printer. With a flexible build platform, troublesome prints could be more easily removed, so he non-destructively modified his printer to have a similar system. [Jan] is clear that this is only a proof of concept, but the test results were good! He printed several jobs that were known to be trouble, and they were all a piece of cake to remove.
[Jan]’s mod consists of a 3D printed, two-piece unit that encapsulates the normal build platform and contains a few strong magnets. A thin sheet of steel sticks flat to this new piece, held in place by the magnets within, and becomes the new build platform. After a print is done, the sheet is removed and [Jan] reports that its flexibility is a big help in removing otherwise troublesome prints, such as the 3D printed solder stencil we covered recently.
[Jan] provides his CAD model but doesn’t really recommend using it for anything other than development work. Results were promising, but there are a number of drawbacks to the prototype. For one thing, it makes the build platform thicker and the Z-axis limit switch needs to be physically lowered in order to zero the unit. Also, the thicker build platform means the volume of resin the build tank can hold is reduced. Still, the idea clearly has merit and shows there absolutely is value in hardware having a hackable design.
[3DPrintFarm] got an early version of the Phrozen Sonic Mini resin printer. If you look at the video below, he was very impressed with its build quality and results. The price is reported to be $200, although we have seen it on some web sites for a bit more. The build quality does look good, although you have to admit, the motion mechanism on a resin printer is pretty simple, since you just need to move up and down.
The printer uses a monochrome LCD which allows it to cure layers very fast (apparently, monochrome panels pass more ultraviolet light through). The panel also has a higher-rated lifetime than color LCDs
[Bunnie Huang] has shared with all of us his utterly detailed teardown on the Form 3 SLA printer from Formlabs (on the left in the image above) and in it he says one of the first things he noticed when he opened it to look inside was a big empty space where he expected to see mirrors and optics. [Bunnie] had avoided any spoilers about the printer design and how it worked, so he was definitely intrigued.
Not only does the teardown reveal the kind of thoughtful design and construction that [Bunnie] has come to expect of Formlabs, but it reveals that the Form 3 has gone in an entirely new direction with how it works. Instead of a pair of galvanometers steering a laser beam across a build surface (as seen in the Form 1 and Form 2 printers) the new machine is now built around what Formlabs calls an LPU, or Light Processing Unit, which works in conjunction with a new build tank and flexible build surface. In short, the laser and optics are now housed in a skinny, enviromentally-sealed unit that slides left and right within the printer. A single galvo within steers the laser vertically, as the LPU itself moves horizontally. Payoffs from this method include things such as better laser resolution, the fact that the entire optical system is no longer required to sit directly underneath a vat of liquid resin, and that build sizes can be bigger. In addition, any peeling forces that a model is subjected to are lower thanks to the way the LPU works.
Details about exactly how the Form 3 works are available on Formlabs’ site and you can also see it in action from a practical perspective on Adam Savage’s Tested (video link), but the real joy here is the deeply interesting look at the components and assembly through the eyes of someone with [Bunnie]’s engineering experience. He offers insights from the perspective of function, supply, manufacture, and even points out a bit of NASA humor to be found inside the guts of the LPU.
[Bunnie] knows his hardware and he’s certainly no stranger to Formlabs’ work. His earlier Form 2 teardown was equally detailed as was his Form 1 teardown before that. His takeaway is that the Form 3 and how it works represents an evolutionary change from the earlier designs, one he admits he certainly didn’t see coming.
Even if you’re pretty sure what the answer will be, a marriage proposal is attended by a great deal of stress to make the event as memorable and romantic as possible. You’ve got a lot of details to look after, not least of which is the ring. So why not take some of the pressure off and just 3D-print the thing?
No, a cheesy PLA ring is probably not going to cut it with even the most understanding of fiancees, and that’s not at all what [Justin Lam] did with this DIY engagement ring. He took an engineer’s approach to the problem – gathering specs, making iterative design changes in Fusion 360, and having a prototype ring SLA printed by a friend. That allowed him to tweak the design before sending it off to Shapeways for production. We were surprised to learn that jewelry printing is a big deal, and Shapeways uses a lost-wax process for it. First a high-resolution wax SLA printer is used to make a detailed positive, which is then used to make a plaster mold. The mold is fired to melt the wax, and molten gold is poured in to make the rough casting, which is cleaned and polished before shipping.
Once he had the ring, [Justin] watched a few jewelry-making videos to learn how to set the family heirloom stone into the bezel setting; we admit we cringed a bit when he said he used the blade shaft of a screwdriver to crimp the edge of the bezel to the stone. But it came out great, even if it needed a bit of resizing. The details of the proposal are left to the romantically inclined, but TL;DR – she said yes.