How to Slice Firearms for 3D Printing

By Sean Aranda (3D Print General)

How to Slice Firearms for 3D Printing

One of the largest barriers to entry in 3D printing can be just how overwhelming the slicing software can be. Most programs attempt to have an “easy” or “basic” mode where you just select a couple of items for your print. Unfortunately, this is not ideal for printing a strong and clean firearm. Once you get into “expert” or “advance” mode on your slicer, you will surely be overwhelmed with the numerous options available.

Which Slicer Program to Use?

Over the years what is the preferred slicer software to use by makers has definitely changed. Five years ago, the paid program called “Simplify 3D” reigned supreme. Due to lack of updates, free and open source programs have certainly surpassed Simplify 3D in user base.

There are essentially a half-dozen slicing software programs that are used daily by most makers, with the two most popular being Cura by Ultimaker and PrusaSlicer by Prusa. Many printer companies have attempted to make their own slicer, but the vast majority of these are just modifications of those two options. For instance, the popular Bambu Lab printers use “Bambu Studio” as their slicer, and even though I really like that slicer, it is based on PrusaSlicer.

I personally prefer Bambu Studio as my favorite slicer, but when I am not using a Bambu Lab printer, I choose to use Cura due to my years of experience with the interface. I suggest checking out both Cura and PrusaSlicer and to use whichever you find mos intuitive.

Follow the Build Guide

While I cover many important settings below, make sure you never stray from the build guide, particularly if you are new to this hobby. I will go over infill and shell walls and other important strength settings, but if your particular build guide calls for different settings than what I mention, follow those. Individual designers have figured out the best settings for their design based off of extensive beta testing, and they may have found methods to save on material and weight that does not require the high settings I mention.

Quality Settings

Quality can refer to a lot of things, but I will be focusing on the two most important: layer height and line width.

Layer Height: A 3D print can only be as detailed as your layer height when referring to the Z-axis. The smaller the layer height, the more layers your print will require to complete, and the more detail that you can achieve.

In general a layer height of 0.2mm would be considered “standard” for 3D prints, with some people preferring 0.16mm. Anything lower than 0.16mm would be considered “high quality”, and anything higher than 0.2mm would be considered “draft quality.”

All other things being equal, a print with a layer height of 0.1mm will take twice as long to complete as a print with 0.2mm layer heights, since it requires twice as many layers. No extra material will be used, but it will take a lot longer to complete.

Line Width: Your line width is dependent on your nozzle diameter and can affect the tolerances of your X and Y axis. The vast majority of printers ship stock with a 0.4mm nozzle, meaning your line width should be within 10-20% of 0.4mm. The majority of the time I will keep my line width the same as my nozzle diameter, unless instructed otherwise. While this is not always true, the general rule of thumb is your X and Y axis tolerances will be roughly ½ of your line width. So if you ever have issues with reading text on the side of your print or fitting two prints together, you can improve this by lowering your nozzle diameter and line width.

Many makers now prefer a 0.6mm nozzle since quality is only slightly reduced, but it can drastically decrease print time, and may even have some extra layer adhesion strength properties. Just keep in mind you should not exceed a layer height of 25%-75% of your nozzle diameter/line width.

Strength Settings

Again, many other settings may affect the strength of your print, but when I say strength I am referring to shell walls and infill. Shell walls refers to how many perimeters will be printed at the width of your line width. Even a cosmetic print should have a minimum of 2 shell walls to make sure the part is not translucent or easily broken.

In general, the more you increase your shell walls, the stronger your part will be when being compressed in the X and Y axis. If we imagine we are printing a skateboard wheel, you can see how increasing the shell walls a lot will increase the strength of this part, since pressure will only be applied to the outside of the wheel. The example below shows the skateboard wheel 100% filled via shell walls, with infill not being a factor.

The above is an extreme example, and it will be very unlikely your firearm will call for this many shell walls. The majority of 3D printed firearms will call for 4-8 shell walls.

Infill is what connects your shell walls to each other on the inside of your print. If you are printing something that is just cosmetic, you can get away with 10-20% infill. This will save a lot on material and print time, but you should not skimp on infill when printing a firearm.

Again, the majority of firearms will have instructions in the build guide for how high your infill should be, but nearly all of them call for either 99% or 100% infill. Personally I think 100% may be overkill, since you get diminishing results in strength the higher infill you go. That said, if the designer calls for 100%, I will print at 100% infill.

Below is the magwell of a UBAR AR-15 lower with 6 shell walls and 100% infill:

The green lines are interior shell walls, the red lines are the outside shell walls, and the orange is infill (100% in a line pattern).

Infill Patterns

Infill patterns can change the strength of your part, but when printing at 100%, it doesn’t matter nearly as much as when printing at a lower percentage. Some designs, such as the Hoffman AR designs, will call for “Aligned Rectilinear.” You can use the “Aligned Rectilinear” pattern so that your infill runs the length of your firearm, which can be beneficial for increased strength, since 3D printed firearms will have the most pressure on the print in that direction. Unfortunately this is not an option on Cura, but is available on PrusaSlicer and Bambu Studio.

After changing the infill direction to 0 degrees, below is an image of the same UBAR magwell with rectilinear infill at 100% on Bambu Studio, running the length of the firearm:

The yellow lines in the above photo are the shell walls and the red is the aligned rectilinear infill.

You are more than welcome to play around with other infill patterns, but when printing a firearm I will stick to either grid, lines, rectilinear, or aligned rectilinear patterns. There are a few exceptions where I may use a different infill pattern, but just follow what the build guide instructs. You can also search for CNC Kitchen’s older YouTube video titled “TESTING 3D printed INFILL PATTERNS for their STRENGTH” if you would like to see how different patterns can affect print time, material used, and overall strength.

Support Settings

Supports can often be one of the most difficult parts of a print to hone in properly, since they are what allows you to print clean undersides for angles on your part. Most firearm models require a lot of support and will often need honing in depending on the material you are printing with.

You can think of supports as scaffolding for your model that are removed after printing. The closer the angle is to being parallel with the build plate, the more likely you will need support material.

The Bambu Studio slicer actually looks at support angles differently, but the vast majority of slicers look at support angles like the photo below:

Which angle your print will require supports for will heavily depend on the material you are using as well as how good your print is at cooling layers. The more cooling your model gets, as well as the more time it has to cool before the nozzle runs over it again, the steeper the angle you will be able to print without needing support material.

PLA Pro/PLA +, which is the most common material used for 3D printing firearms, allows you to print with your active cooling fan at 100% without any worry of layer adhesion weakness. This means it can achieve much steeper angles than other materials without needing supports. I can reliably achieve a 55 degree angle on the majority of prints in PLA Pro. If you are printing extremely fast, or you have subpar cooling, then you may need support structures at a lower angle.

Other materials like ABS can have weak layer adhesion with rapid cooling. Without rapid cooling, it will be much more difficult to print steep angles. When printing in ABS without an active cooling fan, I will generally reduce my support angle to 45 or 40 degrees. This is just one of many reasons ABS or other unique materials can be a lot more difficult to print with than PLA Pro.

Aside from knowing what angle your material and printer can achieve without needing supports, the two most important settings will be your support Z gap and your support interface.

Support Z gap: The support Z gap, or support Z distance depending on the slicer you use, refers to how far the support is from the underside of your print. If this gap were 0mm, then that means the support structures would be impossible to remove. If this gap is too large, let’s say 0.5mm, then the supports wouldn’t be doing anything and the underside of your print will be very ugly. I have found that when I use a 0.4mm nozzle and a 0.2mm layer height, a Z gap of 0.2mm will result in the best combination of clean undersides along with being fairly easy to remove post-print. This gap will change depending on your layer height and line width. This means you will reduce your Z gap for higher quality prints, and increase your Z gap for lower quality prints.

Most slicers used to require your Z gap to be a multiple of your layer height, but many no longer have this requirement. This means you may be able to print at 0.16mm layer heights and have a 0.2mm Z gap. This depends on the slicer you are using as well as whether you are printing in multiple colors that require a prime tower. Usually I prefer to print with a 0.2mm layer height so that my Z gap can be 0.2mm without any issues.

Support Interface: Support Interface refers to the very top of your support structure- the area that will touch the underside of your angles. I prefer to have a support interface since it allows me to keep my main support structures at a lower percent infill as to save on material and time, and then have the area touching my print be a higher percent infill for better quality undersides. The higher your support interface density, the cleaner the underside of your print will be, but it can also make it more difficult to remove the supports.

When using a 0.2mm Z gap, I prefer to keep my main support structures at around 12-15% infill, and my support interface be 70-90%. Below is a screen shot in layer mode for a UBAR with my support settings:

The light blue in the photo above is the main support structures at 13% infill and the dark blue is the support interface at 80% infill in a concentric pattern. You can play around to find what works for you, but below are my support settings that I like to start with when using PLA Pro, and they should work as a great starting point for you:

Bonus Tips

We will be back in our next article coveringb some slicing setting tips that can improve the print quality and strength of your 3D printed firearm!