3D Printing for Gunsmiths

I first started 3D printing over ten years ago on October 25, 2011 with one of the earliest consumer machines, a Solidoodle 1. At the time, I wasn’t a gunsmith. I started as an airsmith by modifying airsoft guns and I bought the printer to make airsoft gun parts. About a year later I started learning gunsmithing and began the quest for a durable printed AR lower, which is still an elusive goal. Here are the fundamentals. A 3D printer works like a hot glue gun if it were being moved around by a robot arm.

It squirts out semi-molten plastic which is fed into it in wire form like a MIG welder. This plastic wire is called filament and it resembles weed trimmer line. You can buy filaments made from many types of plastic and even blends of different plastics and composites made of plastic plus additives or fillers. You can also make your own with a do-it-yourself extrusion machine and some people have had success just using trimmer line, which is nylon.

A 3D printer works by adding layer by layer, with each layer being across-section of the part at a particular height, hence why this is also called additive manufacturing. The 3D printer "draws" this cross-section onto the build plate (also called the bed) and then moves the bed down one layer and draws the next layer. This process is repeated until the entire part has been finished, from bottom to top. This process is called Fused Deposition Modeling, or FDM.

There are other kinds of printing processes, with SLA (Steriolithography) being the second most widely used behind FDM. SLA printers are also called resin printers because they use UV light to cure a liquid resin like your dentist uses. FDM is the cheapest and easiest process, so it will be the focus of this article. Printer Hardware We’ll start with the hotend, which is the nozzle, heater block, heater cartridge, and thermistor.

The heater is driven by a 12 volt or 24 volt heater cartridge to melt the filament just before it reaches the nozzle. On the cold end is the heatsink and fan that prevents heat from creeping up the filament path and melting the filament too soon. The heat break is a threaded pipe made of a low heat transfer material like stainless steel or titanium. This connects the hot and cold sides and slows down the transfer of heat. The extruder is a stepper motor driven hobb gear and sprung idler pulley.

Filament is pinched between the gear and idler so it can be pulled off the spool and pushed into the hotend. There are direct extruders and Bowden extruders. Direct extruders are mounted on top of the hotend while Bowden extruders are remote mounted and push filament to the hotend through a Teflon tube. The motion system, also called the gantry or "kinematics", is the linear bearings, rods, rails, stepper motors, lead screws, and belts/pulleys that drive each axis of motion.

Usually, the Xand Yaxis are belt driven while the build plate/bed (Z axis) is moved up and down on lead screws. The bed is where the first layer is deposited and most models are heated from underneath. The part fan cools the freshly extruded plastic; too much cooling makes the print weaker while not enough allows the resolution to become reduced because fine details will droop. On the software side, the file formats for printed parts are usually.stl, or.obj.

The STL file format was native to stereolithography computer aided design software and has since spawned several backronyms such as "Standard Triangle Language" and "Standard Tessellation Language" while OBJ is stands for object. You need a program called a slicer, which slices the part file into layers and generates the G-code the printer needs to draw each layer.

This is the same G-code used by computer numerical controlled machines, the only difference is where S#### would be spindle speed on a mill, for a 3D printer it is hotend temperature. The bed is also heated, which helps ensure first layer adhesion. If the first layer fails, the whole print fails. All printer software uses the metric system, millimeters for movement and degrees Celsius for the bed and hotend. The type

of plastic filament you use determines the print temperatures. For most prints the default slicer settings will be okay, but be sure to select the right material because the default settings differ between materials. Also related to software is the design aspects of 3D printing. You don’t have to learn a CAD program to print, however, it helps you to understand the structure of the part you are printing, as well as allows you to modify parts or create your own.

When I started, the best free program was Sketch Up, so that’s what I learned and still use. It is probably the easiest to learn. To use Sketch Up, you just draw a 2D profile of your part, extrude that profile into a 3D shape, then start modifying with things like radiuses or filleted edges, holes, grooves, etc. You can even add engraved or raised text to apart.

Today, a better CAD program is Fusion360, but be warned, Autodesk has a history of abruptly jacking up the price on cheap or free programs, switching to a subscription license model, or just abandoning some of their past programs just as they became popular. Even Sketch Up has switched to subscription or cloud based services, but you can still find standalone, offline installers for their older versions (2018 and earlier).

Getting Started This might all sound pretty complicated but running the printer is easy once you get the workflow memorized. The first step is to select the STL or OBJ file of the thing you want to print. You can download a file made by someone else, possibly for free, or design your own part and save it as a suitable file. Open that file with a slicer program like Slic3r, Cura, or Simplify3D.

Position the part where you want it on the build plate, then open the settings menu to select the material you want to use, and click "slice". This will generate a G-code file. Save this to your desktop, then put it on a micro SD card or other suitable storage device. Make sure the print bed is leveled, use the manual controls on the printer to bring it up to temperature, then pull some filament off the spool and load it into the extruder.

The extruder arm is spring loaded; hold it open and feed the filament in by hand until you feel it reach the nozzle and start melting. Keep pushing some filament in and watch it extrude to make sure the nozzle isn’t clogged. Spray some cheap hairspray or rub a glue stick onto the bed as this helps the first layer stick. For most printers all that’s left is to insert the SD card, select the G-code file you saved on it, and hit print.

Some older printers are fed G-code from a computer connected over USB (Universal Serial Bus). Watch the 3D printer print the first layer and make sure there aren’t any problems. Once you see

the second layer properly fuse to the first, it’s hands-off from there, however, you should stay in the room and keep an eye on it while you work on something else. There is a remote chance of afire hazard. If the print comes off the bed and sticks to the nozzle or if a heater wire shorts, it can catch on fire. Filament Types PLA (Poly Lactic Acid) is the cheapest and most common filament. It is the lowest temperature printing material at 190-210C.

It doesn’t need a heated bed because it doesn’t warp, making it the best choice for fine details if you use a greater than 50% speed on part cooling fan. It’s one of the highest tensile strength materials and is very stiff, but it can also be brittle. PLA parts usually fail by cracking. Its major flaw is service temperature. One of my first majorly printed gunsmithing projects was a Groza bullpup AK conversion kit for an AMD-65. It had lots of printed parts in direct contact with the barrel, trunnion, and gas tube.

These held up great during shooting, even after a few mag dumps, but softened and warped in my truck on a hot day. Almost no consumer products are made of PLA. ABS (Acrylonitrile Butadiene Styrene) is the second most common material. On paper it is weaker than PLA, however, it has better impact resistance and is not as brittle, so in practice the parts seem to be stronger. It prints at higher temperatures (225-245C) and requires a heated bed at 60-80C.

It also needs an enclosed printing chamber because the parts will warp and lift off the bed in room temperature air. To avoid warping they need to be cooled down slowly after the printer is finished. It’s usually okay to just leave the door closed and let the chamber cool down. Lego bricks and many other consumer products are made of ABS. An alternate version is called ASA (Acrylonitrile Styrene Acrylate or Acrylic Styrene Acrylonitrile) which is better for outdoor use because it is more UV resistant.

PETG (Poly Ethylene Tetraphthalate-Glycol modified) is the third most common filament and its properties area middle ground between PLA and ABS. It prints around the same temperatures as ABS but doesn’t warp as badly so it doesn’t need an enclosure, only a heated bed. This material is similar to the types of clear Polyethylene used in water bottles. Nylon is a more advanced material. It prints at 240-260C with a heated bed set above 80C. It warps like ABS and also requires an enclosure.

Like PETG, Nylon is an excellent all-around material but with much higher strength. It has the tensile strength of PLA and the impact resistance of ABS but its major flaw is low stiffness, being lower than PLA but higher than ABS. This can be eliminated with fiber fillers like carbon fiber or glass fiber, both types are available as composite nylon filament. Glass filled Nylon is the material of choice for most polymer framed pistols and gun accessories like grips, handguards, and stocks.

PC (Poly Carbonate) is a very advanced material with properties are similar to ABS but much stronger. PC requires a very high temperature printer, printing at over 280C in the nozzle, an over 100C bed, and needing an actively heated enclosure. The previous mention of heated enclosures were passively heated by the bed heater. Polycarbonate is used to make Blu-ray discs, safety glasses, car headlight housings, and electrical equipment due to its high service temperature and insulating and flame retardant properties.

TPE (Thermo Plastic Elastomer) is used to print flexible parts, like recoil pads for a rifle stock. It can be difficult to print with and can’t be printed on a Bowden extruder type printer. Its nozzle and bed temperatures vary widely because there are many different chemical formulations of TPE, but what they all have in common is they have to be printed slowly and with a lot of cooling fan speed (>75%).

I’m not sure what consumer products are TPE versus regular rubber but TPE filament feels a lot like a rubber band. PVA (Poly Vinyl Alcohol) is used as a support material in dual extruder printers because it melts in plain water. This makes cleanup of complex prints much easier, because the alternative is to print supports (like scaffolding) of the same material as the part, which bond to the part and have to be filed or Dremeled off. PVA is the main ingredient in Elmer’s glue.

On to blended or alloy filaments. These combine two chemically-compatible polymers to form an alloy with combined properties. The two that are most common in printing are PC blends and anew type of filament that manufacturers refer to as PLA Plus, Tough PLA, or impact modified PLA. The PC blends are usually PC- ABS, but the Polymaker brand doesn’t specify the other polymer.

They deserve specific mention because their line of PC blends are the strongest materials I have tested and they print at lower temperatures, meaning they can be printed on cheaper printers. The PLA Plus style blends are also mostly unspecified, but I believe they are blended with ABS or PETG. They sacrifice some tensile strength and stiffness for higher service temperature and better impact resistance. Some of them also warp, so a heated bed and enclosure are needed.

There are two main types of composite filaments: fiber filled and powder filled. Both can be made with any type of plastic, however, powder-filled composites are usually PLA and the most common carbon or glass fiber filled filaments are nylons. Fiber-filled composites have much greater stiffness and slightly greater tensile strength. Powder additives may include sawdust, powdered minerals, and metal powders. They are usually added for aesthetic purposes, which is why PLA is the main plastic of choice.

You can find composite PLA filaments that look like many different kinds of wood, stone, magnetic iron, stainless steel, bronze, copper, brass, aluminum, and even bismuth/tungsten, which is used for printable radiation shielding. I’ve printed handguards with wood PLA that are hard to tell apart from real wood, especially if you orient the print so the layer lines look like wood grain, and then sand and stain it. Your First Printer Should you buy a printer?

A gunsmith has a lot of uses for a 3D printer, even if not the obvious "print a gun". You can do customized grip panels, 1913 rails, or M-Lok accessories, stocks, handguards, cheek risers, magazine extensions or base plates, AR or AK pistol grips, even recoil pads and elastic buffers. You can also prototype your own designs and make special tooling, jigs, and fixtures. I would not advise printing whole guns or receivers for customers, although it’s not illegal as the media would have you believe.

If you are an FFL 07 Manufacturer, serialize the receiver on an inset metal plate and record it like any build. The problem is liability and customer satisfaction. Using current technology, 3D printed receivers just won’t last as long as a traditional metal gun and might break at a bad time. Another good reason to buy a 3D printer is they have gotten much cheaper. When I bought my first one in 2011 it was $1,400 and filament was $60 per kilogram.

Today, you can get a decent machine for just under $200 on Amazon and some filaments are as cheap as $15/kg. The most popular printer right now is the Creality Ender-3. I bought one recently and have been using it to print samples for filament testing. That way I know whether or not a certain filament can be printed by the majority of the printer community, who use cheap printers similar to the Ender-3. Just like any industry, printer filament manufacturers are known to exaggerate in their marketing materials.

For the most part you’re not going to find a bad filament and they all print okay, but some of us are looking for the absolute strongest material we can print with. Because of this I started aside project to independently test as many high strength filaments as I can. If you want to support my testing efforts and see the results, check out my Patreon page at Patreon.com/Print- Science. 3D Project Example Additive manufacturing is a useful and increasingly accessible method for making tools and parts.

There are a lot of things you can build with a 3D printer. Here’s how I designed and made 3D printed firearm wall hooks. These wall hooks for guns I recently made area prime example. You could spend anywhere from $15-50 on a pair of metal hooks, or, if you have a printer, you can make some for less than $2. Whenever I want an item and think that it could be made with a 3D printer, the first thing I do is check Thingiverse.com to make sure somebody else hasn’t already designed it or something similar.

Thingiverse is a wonderful resource for many different types of 3D printing projects. While firearm parts and accessories are officially against their rules, you can still find tons of stuff like AR or AK grips, Picatinny, Key Mod, M-Lok rail accessories, and even bipods and stocks. These are usually labeled as "airsoft" parts. There are other websites to look for files as well. GrabCAD.com, Yeggi.com, STLFinder.com, and Cults3D.com are good sites to search for projects.

Grab CAD isn’t necessarily geared towards printable models but there are thousands of them on there. Yeggi and STLFinder are search engines that aggregate the 3D models available from many sources. Cults3D is the closest to Thingiverse because it has exclusively printable 3D models. The main difference is Cults allows artists, engineers, and designers to charge for their models, so sometimes you find some cooler stuff on Cults.

So I searched "gun wall hooks" and many variations thereof (hanger, mount, holder, etc.) on Thingiverse and found about a dozen models.

I printed these in ASA, which is around 4.8 cents per gram, so $1.66. Some of those were direct wall mount, others for pegboard or Open Armory system, some square, some curved, however, none of them were particularly of interest me. I was looking for something that looks cool, minimizes material usage, and is strong enough to hold heavier guns. So I decided to design my own. I did a little research on the shape of wall hooks.

If you look at some skeletonized designs they resemble what you’d see in a roof truss, with the long sections that form the perimeters being reinforced by a crossmember at the spot where they would most likely buckle. What’s different with my design is the crossmembers are replaced with circles, also called hoop reinforcements. If you load the center of an arch, it transfers that load to the edges. A circle is just an infinite arch, so the load is transferred to every other point the circle touches.

This is stronger and uses less material that the normal truss type reinforcement s. The curve on the front face of the hook works the same way; in order for the hook to flex forwards, the curved part would need to either buckle inwards towards the circles or outwards. Either way it is reinforced by the circles, as they would have to stretch or collapse before the hook can fail. If this were milled from aluminum or cut from wood, it would just look like a hook with holes in it.

However, these were printed with no walls so you can see the internal honeycomb structure, which is unique to 3D printing. Printers can make parts that have solid perimeters, tops, and bottoms (also called shells) and internal infill patterns of varying density. These hooks were printed with 35% infill in the full honeycomb pattern. The honeycomb pattern has a line every 120° and these lines zig-zag at 60° and align on top of each other to form hexagon cells.

Fast honeycomb skips one line on every other layer, while full honeycomb prints a fully enclosed hexagon cell on every layer and doubles one of the zig-zag lines side-by-side so that every single width line in a layer is sandwiched above and below by a double width line, making it very strong.

At bottom, grid infill. On right, triangle infill. Other infill patterns include rectilinear, grid, and triangle. Rectilinear is a tight grid pattern with lines that alternate 90° every layer, so up-down lines on layer one and sideways lines on layer two. This is fast but weak as they only bond at the vertices. Grid is a little better as it is a larger pattern of squares that are filled in more solidly, similar to full honeycomb. Triangle is probably the best compromise between speed and strength.

It lays a solid line every 120°, every layer, and they fuse very well at the points where they overlap as well as along each line. Also, all these patterns can be manipulated by adding solid layers every so often and by doubling up layers. Solid layers are sort of like firewalls in a building; they enclose parts of the model’s internal structure with solid bulkheads and can be added at different layer intervals at around every 50 layers or so.

Doubling means printing two or more layers of perimeters or shells before the printer lays down the infill. If your layer height is set to 0.1mm and the interval set at two layers, the printer will print two layers of perimeters before it starts to print the infill. When it does it will print the infill at double the layer height (0.2mm) to make up for the skipped layer. This makes the infill stronger and saves print time, while still allowing for fine detail resolution on the outer skin (or shell) of the model.

As for the wall hooks, they can be printed with any settings you want. I only omitted the outer shells to show off the infill pattern and to prove their strength. So far they have held up a SPAS-12 shotgun weighing 11 pounds with no problems. If you print them with enclosed walls they will be even stronger—just be sure to use good drywall screws! You can see this design at Thingiverse.com/thing:4910792 and my other designs at Thingiverse.com/ giterdunn. AG