Creating ultra smooth parts with residual resin?

Hi all,

Has anyone had experience making smooth surfaces with their prints with leftover resin? For some of our work, the 50 micron resolution may be too much of a surface roughness for some of our experiments, so I was wondering if anyone tried making a smooth finish by brushing uncured resin onto their prints and placing those brushed prints in a FormCure. Sanding is not really an option since a lot of our prints will have a lot of delicate features.


I’ve used a coat of polyurethane for it by dipping and slowly retracting it out of the liquid(The slower, the thinner the coat). Can be done with resin but the high viscosity leaves a thick layer.

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You’re going to lose your detail by trying to coat it in resin, it won’t get thin enough.

You can try a spray but I would test that first, you can also try using an air blaster sander, where it’s basically spraying some kind of abrasive material (like baking soda) to smooth the surface. Otherwise you have to sand by hand very carefully.

A thought.
What if you mix IPA with the resin coat before application?

I’ve noticed that when my IPA Clear-print-cleaning container is about to need fresh IPA, some of the prints will come out noticably clearer.

Mixing IPA with resin is going to render the resin uncurable which won’t do you much good. There are two-part resins designed for this kind of application that can be used with thinning solvents like Acetone. XTC-3D is one that I’ve used a bit. Filler primer is also good for this sort of thing, and goes on a bit thicker than conventional primers.

We don’t have any fine details since it’ll be “flat”. As long as there’s not roughness associated by the layers that’s okay for us since we are not have very detail intricate features.

Spraying isn’t an option or an air blaster sander since we need thoroughly clean our prints for our applications.

Unfortunately I need to use a biocompatible material (We’re using dental resin), but I wanted to ask around since I would hate to use an expensive resin on a trial/error experiment.

I have a similar question here: hoping to get a very smooth surface inside what is essentially a tube that opens up (think: pumping liquid through a loop, and making one segment “open” to allow for dissolved solute sensors to be inserted into the tube). As this shape will be fairly unique, we are printing this component; however the liquid medium will have algae in it, which requires smooth surfaces to mitigate biofilm buildup.

Using two-part resins with a thinner, like Acetone, as Frew suggested abv, sounds like a possible solution; however I am very new to using this medium and wanted to see if there are any (1) application methods, (2) specific recipes, and (3) general warnings that the good folks on this forum could provide before we start experimenting away.


Look into the white paper by formlabs on how to print a camera. I think they used uncured resin to make the lens flat and clear.

You need something thinner, the resin by itself is too thick for most applications.

Thanks I’ll take a look at that!

Just a thought, and this has been driven by our need to build thin membranes, our print chamber temp is controlled to 37 deg C (F3 chamber set at 35 deg C and of this morning my F2 is set to 35 degC via FL software) This was to reduce the resin viscosity so as not to create resin puddling around the supports that flowed onto our product.

Using appropriate PPE and checking flashpoint of dental resin, heat a small beaker of resin and dip your part and observe how it drips off. The lower the viscosity the thinner the film you will be left with due to surface tension. You may also need to keep your environment warm as well, so that the viscosity stays low will dripping.(low temp oven?)

You do not change the chemistry of the resin nor the biocompatibility ( actually, depends on conditions that FL have submitted as cured parts, ie FL may have set process conditions bands with respect to environment temp, laser cure energy and cure time and temp etc )

Also put in a sacrificial spike to draw off excess resin away from your part.

In short play with the surface tension by controlling temp. Have used these techniques with many polymer resins besides UV cure.

The inspiration came from nature by watching rain drops pool and drip off leaves and branches many years ago.

Let me know how you get on if you try it.

Biofilms are a bugger and you may still not get a smooth enough surface to disrupt their adhesion.