Resin 3D Printers – A very entry level primer (Part Four)

Full disclosure – this is where I’m least familiar. I’ll talk about what I do know, however there is are a lot of opinions on what I’m about to tell you. These are mine, and to be honest I’d love to hear others. I’ll also try to be honest where my knowledge is hazy. Also, these instructions are for the Elegoo Mars printers (and anything that comes with the ChituBox software really).

First up; a quick introduction to how a 3D model works. All 3D printers (at least to my knowledge) work on the concept of slicing a model into sections, similar to an MRI or that creepy horse scene in the movie “The Cell”. These layers determine how the printer will move it’s build plate and how to “draw” the picture. Taller models will require more slices, as will printers with finer resolutions.

Also; a 3D print typically requires a support structure or scaffold. These are throwaway pieces that are used to support areas that would normally have nothing underneath them. 3D models can come unsupported, or pre-supported. Unsupported models can have supports manually or automatically applied to them through software, and pre-supported models are already optimized for support by the designer. Pre-supported models generally cost more because a lot of thought has gone into the process of creating the supports with as few contact-points as possible. (Which means less cleanup after the print is completed). (Update – 02/26/21: Reading more about this, there are lots of varying opinions on pre-supported models. A unifying thread however is that pre-supported models; while a good concept, are sometimes more prone to failure because the designer didn’t take into account the needs of a user’s particular printer. Something to keep in mind I guess…)

On top of slicing and scaffolds, there’s also internal scaffolding (Called “Infill”) to consider. Basically a 3D model can be as hollow or solid as you’d like, however by making a model solid unnecessarily, you’ll be wasting resin. Usually a model is then hollowed out so only the outer 2-3mm are solid, and the interior is filled with a grid scaffold to keep it structurally strong. This can be a double edged sword and I’ll discuss why this is, further below.

For Elegoo Mars printers (and others that use the same control boards), the software that works with these files is called ChituBox. It comes for free with the printer, and honestly I think works really well. There are other programs available as an alternative to ChituBox. A good example is PrusaSlicer; which comes highly recommended on Reddit. At the end of the day, if you have an Elegoo Mars you have to use ChituBox to create the final file for print as it writes in a proprietary .CTB format. That doesn’t mean you can’t slice and create supports in another program, and then import them into ChituBox for conversion to .CTB. There are a lot of options out there, these are just two I know of. Just know that if you have an Elegoo printer, you’ll be using ChituBox at least a little bit. Since it’s what I’m most familiar with, I’ll be discussing ChituBox exclusively. Other programs will likely operate in a similar manner.

Once you have ChituBox installed on your PC, you’ll need to set it up for the parameters of your printer. Generally speaking most 3D printer manufacturers have a guide on how to do this; but the big variables are: size of build plate, initial layer curing time, and subsequent layer curing time. Layer curing times are based on the printer, strength of the UV backlighting, and the type of resin you’re using. You can also choose how solid or hollow you’d like for your model to be, and we’re ready to start working.

Open up a downloaded .STL model (ChituBox supports these natively). It’ll appear in 3D on the virtual build plate on the screen. The size of the model is “lifesize” in relation to the virtual build plate on the screen. If you open the size parameters for the model, it’ll show you actual model size on the X/Y/Z axis in millimeters. Basically it’s the ultimate “what you see is what you get”. You can move the model around, rotate and scale it as needed. You can also clone it to make copies. I’d recommend setting the size, and the rotation / position of the 3D model first, because cloning also clones these variables. Pay attention to the amount of models on the build plate; you’ll want to leave a gap between each model and make sure they aren’t overlapping. Otherwise you’ll have a “model -> scaffold -> model” sandwich on the final print. Something else to consider is scaffolding/supports appear from below between the build plate and the model. Finer details that are harder to sand should generally be facing upward, as they won’t have supports attached to them.

Once you’re happy with the amount of models on the build plate, on the top bar there is an auto-layout button. This will position everything on the plate so it best fits for printing. I personally use this function, however I can see where you’d want to override it. This is definitely one of those “everyone will have a different opinion” areas.

After this is done, you can add the supports to the models. You can either add supports to each model individually, or let ChituBox do it for all models at the same time. Personally I’m too new to really know how to scaffold these myself, so I use the auto-support option. To do this, I just click the “Select all models” box and then open the supports tab. Clicking + All near the bottom will auto-support everything. You can see these supports being added in real-time. In most cases it can be rather shocking at how many supports are added – don’t worry this won’t add to the overall print time. (The additional cost in resin is negligible as well.)

Now that everything is supported and you’re happy with the final layout, we’ll need to slice the model. Slicing will do two things:

It’ll hollow out the overall model and add interior supports. Depending on how you setup your printer/ChituBox, models will be more or less hollow overall. If you have a very thin sidewall and minimal support inside the model, it’ll be flexible and prone to damaging/breaking. It may also have problems printing. Also (and I’ve found this out the hard way), hollow models can contain liquid resin after the print is completed. I printed a bunch of 32mm bases that were fully hollow (with no interior support), and they were full of liquid resin after the print finished. Each one had a small pinhole in them I could squirt the resin out of by squeezing the base. This was resin that was fully wasted because I didn’t realize it was there until I was washing the bases in water.
After the model has been hollowed and interior supports added, each layer is sliced. Once again, the closest thing to this is an MRI – basically the entire model is divided into thin wafers/discs, and these are what are “printed” by exposing the resin to the UV light.
Slicing is really easy – you just go back to the models list, and click the “Slice” button. The system will slice the model layer by layer (and show a preview of what the sliced layers will look like). Once this is done, you just need to save the sliced file in ChituBox .CTB format to a USB drive. If you like the way the model was setup for print, save a copy to your computer as well. It’ll make reprints easier if the USB drive fails.

Next, we’ll talk about how to print and cure this model using the Mars Pro printer.

Throughout this series, I’ve been showing off the Barbarian Chieftan sculpt by Matt Gubser of Prophet Miniatures. I’m not affiliated with Matt or Prophet in any way, I just think it’s a great sculpt that prints well. You can find the .STL at Matt’s page on MyMiniFactory.

Author: Greg

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