UV Resin Perfects 3D Print, But Not How You Think

At this point, everyone knows that the print quality you’ll get from even an entry level UV resin printer far exceeds what’s possible for filament-based fused deposition modeling (FDM) machines. But there’s a trade-off: for the money, you get way more build volume by going with FDM. So until the logistics of large-format resin printers gets worked out, folks looking to make things like replica prop helmets have no choice but to put considerable time into post-processing their prints to remove the obvious layer lines.

But thanks to this somewhat ironic trick demonstrated by [PropsNstuff], you can actually use UV resin to improve the finish quality of your FDM prints. The idea is to put a layer of resin over the layer lines and other imperfections of the 3D print, cure it with a handheld UV flashlight, and then sand it smooth. Essentially it’s like using resin in place of a body filler like Bondo, with the advantage here being that the resin cures in seconds.

The thick resin fills in tough spots quickly.

Now to be clear, this isn’t a new idea. Our very own [Donald Papp] investigated the process back in 2018, and [Thomas Sanladerer] covered the idea in a video of his own the following year. But the difference here is that [PropsNstuff] doesn’t just coat the whole print with resin, he takes a more methodical approach. Working in small sections, he targets areas that really need the high-build properties offered by this technique.

With the tough spots addressed, he then moves on to coating larger areas with resin. But this time, he mixes leftover resin from his SLA printer with talcum powder to make a mix that can be brushed on without running everywhere. It takes a few thin coats, but with this mix, he’s able to build up large swaths of the print without losing any surface detail.

Is it still a hassle? Absolutely. But the final result does look spectacular, so until we figure out how to build the replicators from Star Trek, it looks like we’ll have to make up for our technological shortcomings with the application of a little elbow grease.

Thanks to [Zane] for the tip.

18 thoughts on “UV Resin Perfects 3D Print, But Not How You Think

    1. Aren’t the replicators essentially the same as the transporters but they pull from preset data instead of beaming up a person and then re-assembling them elsewhere?

  1. I don’t wanna be the spoilsport, but I think it’s important to note the safety implications of using this stuff like this — it’s nasty in its uncured/under-cured form, and while careful brushing can be done (please gods don’t aerosolize it with a spray bottle or air brush) while keeping it contained, and then the workpiece cured, doing the work inside means any lapse in care could be contaminating a workspace where it will not readily cure. Even not being thorough with curing before sanding could lead to some real bad times.

    As with any material you’re not familiar with, check your MSDS’s and plan around the safety advice contained within — if you don’t understand why the recommendations are made in them, you probably don’t understand the material well enough yet. Even if you are going to use such resins in an off-label manner like this (look, I know what website I’m on…), understanding the risks can inform you on how to do so more safely.

    Volpin Props has a good thread on this exact topic, with alternatives provided (eg urethane filler primer, which is what I’ve started using myself to great results, and he also points to more-appropriate UV primer products as well):


    Volpin’s got way better bona fides than I do in this space; if he says something’s safer, easier, and cheaper in practice, sounds good to me.

    1. Polyester resin based body filler is usually full of ‘micro balloons’, especially if it says light weight on the label. That produces a somewhat porous surface that must be filled with primer. These fillers also cure very quickly so one must work fast and be resigned to disposing of some once it ‘kicks’ and becomes too stiff to apply.

      The cure time can be extended a bit by using the bare minimum of catalyst required and working in cold temperatures, but too little catalyst or holding it too cold for too long will result in a mess that will not cure.

      Applying a little UV curing resin goes on smooth and curing can be easily controlled with the UV light.

      1. I think most people are referring to a sprayable primer/filler that is applied with a spray gun and dries in minutes. Think of thick paint. You are thinking of something more like Bondo filler.

  2. Seems to me that something like epoxy (just another resin) would be cheaper and achieve the same thing. Also, like the body filler/primers for this. The reason we don’t use UV resin for such large objects is the expense of both the resin and the optical technology (large LCDs or other device to expose the resin). There is no need to use such an expensive material just to smooth a surface. As far as quick curing, automotive primer fillers can be dry in something like ten minutes which is way faster than the resin process in use especially considering the process time.

    1. Did you even watch the video? He goes from applying to sanding in literally seconds after hitting the resin with UV light. Waiting 10 minutes is an eternity in comparison.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.