3D Printed Gears: How to Make Them

3D printing gears is possible, sometimes even preferable! Easily learn how to make 3D printed gears that fit your needs.

Gears are one of the most basic components for transmitting motion in mechanical assemblies. They date back to at least the 4th century BC in China and today can be found in many applications, from small clocks to bulky automotive transmission boxes.

Although it may seem counterintuitive at first, 3D printing gears is not only possible, but also very useful. Although 3D printed gears are inherently weaker than their metal and plastic counterparts, they are still suitable for a wide range of applications. However, we must consider their limitations in terms of material and dimensional accuracy.

Whether it's a newly designed project or replacing parts, designing and 3D printing gears is always a good choice. In this article, we'll go over some important tips, starting with a brief overview.

Gear 101

Gears are awesome, useful and obviously fun. But how do they work and what can they achieve?

In their most basic form, gears use meshing teeth to transfer and transform rotary motion between them. Gears of the same size simply transfer rotation from one gear center to another, while gears of different size can change speed and torque.

One of the most basic principles in mechanical gears is that one tooth of rotation on one gear corresponds to one tooth of rotation on its partner. Consider, for example, meshing a 15-tooth gear with a 60-tooth gear. A ratio of 60:15 equals what it is called gear ratio (in this case it is 4), which means that the small gear rotates four times for each rotation of the large gear.

The slower rotation of the 60-tooth gear gives it more turning power, known as torque. In this case, speed is traded for force, and this is just one example of how gears can combine to create complex mechanical interactions.

Tip #1: Plan ahead

To successfully make 3D printed gears from scratch, planning and testing is highly recommended.

First, you'll need to determine your goals. Where will these parts be mounted? Will they be used for a short or long time? For replacement parts, what materials were used on the original parts? All these aspects will affect both the design and the choice of materials further down the line and should be considered from the start.

Test your printer

It is very important to know the limitations of your 3D printer in terms of tooth size. The example in the photo above, of this test gear impression, is a great starting point. Check for accuracy and be sure to use the same material you plan to use for the final gears.

Size matters

Once you know how small you can go, you also need to know how big you can go. Larger gears allow larger teeth for the same ratio. Larger teeth are also stronger, can better handle tolerance errors, and are easier to post-machine.

On this note, keep in mind the face width, which is the "height" of a gear if it is laid flat on a table. Often defined using various rules of thumb, width is directly related to gear strength and should therefore be well thought out.

Joining the shaft

Finally, consider the shaft join. This is how the gears will be attached to whatever shaft you are using. This interface plays a major role in the transfer of motion and is very likely to be a point of failure in your design since shafts are usually made of metal, especially in motors.

A non-circular joint such as a hexagon is a good alternative, along with the use of ball bearings and other device mounts.

Tip #2: Design

3D printed gears are easy to prototype, but well-functioning ones depend heavily on some key parameters. Modern facility design is a 100-year-old discipline that involves a lot of physics. And although there are many gears, the involute spur gear is the most common.

When designing a classic gear, important parameters include pitch diameters, pressure angles, face widths, center distances, modules - the list goes on. Although we won't go into detail here, there are many online sources and interactive tools.

Nevertheless, the most basic principle in the design of involute gears is that the mating surface between two teeth occurs at a single point. And this is possible only with the help of a certain tooth profile made of involutes on a circle, hence the name.

Designing a gear from scratch will require spending some time learning gear parameters and using tools like Gear Generator. This website creates cylindrical gears based on dimensions entered by the user. These details include the number of teeth, pitch diameter, diametrical pitch and pressure angle. Since these terms are a bit specific, you will need some knowledge of gears to use the Gear Generator successfully. However, if one parameter is changed, all related dimensions will be changed proportionally by the website, so functioning equipment will be produced regardless. Once the gears are designed in Gear Generator, they can be downloaded as a DXF or SVG file.

Gear Generator isn't the only handy option you can use to generate gears. Fusion 360 there is a Spur Gear add-on available that requires knowledge of several design parameters in addition to those mentioned for the Gear Generator. Modulus, Backlash, and Fillet Radius values are required, making the Spur Gear plugin flexible but slightly more demanding to create gears.

If you are a beginner, Tinkercad can also be a useful option. You can use the program to create cylindrical gears, which are available in the Shapes library. This is the simplest option we mentioned, and requires significantly fewer parameters to create gears. Just be aware that testing may be required to ensure the product is working properly, as results are usually less accurate. Otherwise, simple facility designs for new projects can be obtained through online repositories such as McMaster Carr, 3DContentCentral, and GrabCAD.

For those looking for replacement parts, Stephan from the CNC Kitchen YouTube channel has a video that covers how to design a replacement gear using reverse engineering and the Fusion 360 add-on.

Tip #3: Materials

Let's face it: 3D printed gears will never be as strong or durable as injection molded or machined parts. However, given the wide variety of plastics available for 3D printing, there are many applications for which 3D printing can be suitable or even superior in functionality.

In terms of durability, Nylon (Polyamide) is the first choice, especially for lubrication-free operation. Although relatively difficult to 3D print, polyamide has the strength and flexibility needed to make durable plastic gears.

To reduce printing hassles, more common 3D printing materials such as PLA+ ABS or PETG can also be good choices. They are recommended over the more popular PLA, a brittle material that easily "snaps" under stress. PLA+ is recommended because it offers improved strength and flexibility and can be used for functional parts. PLA+ parts tend to provide more flexibility and withstand pressure better than traditional PLA, making them preferred for 3D printing devices.

PETG is a better option than PLA because it won't break as easily under pressure and has good resistance to heat generated by friction.

Tip #4: 3D printing

It's finally time to materialize your gear. Here are a few things to keep in mind when it comes to 3D printing:

• Orientation: Print gears face down. The way the layers are deposited in this orientation will make the teeth stronger.
• Parts cooling: Especially in the case of PETG, turning on the fan to cool parts can actually weaken 3D prints. Turning it off allows the layers to fuse together and increases strength along the Z axis.
• Flat bed: Make sure you have a perfectly level print bed. When printing gears face down, any unevenness in the bed will create distortions that will likely affect functionality.
• Height of the first layer: Adjusting the initial layer height is another way to improve part accuracy. Increasing the initial layer height one step higher, for example up to 0.25 mm for a 0.2 mm layer height, can reduce elephant foot and improve functionality. If the nozzle is too close to the bed, the first layer will come out crushed and generate tooth deviations that will not allow proper bonding. Alternatively, consider using  rafts.
• Layer height: Even though stress is placed on the XY-axes (assuming the gear is printed face down), layer height can still affect the overall strength of the part. Lower layer heights, such as 0.1 to 0.15 mm, will make for a stronger and more homogeneous structure.
• Hot end temperature: The higher temperature of the hot end will improve the adhesion of the layer, similar to the way it reduces the fan speed to cool the part. 210-220 °C is a good starting point for PLA and 230-250 °C is good for PETG, although it is important to note that different brands have different manufacturer recommended settings.

• Filling: As one of the most important settings for printing gears, proper filling will greatly improve the strength of the part and potentially save a lot of frustration. It is recommended to increase the percentage from 50 to 100% and use  cubic, gyroid, or some other strong fill pattern.
• Printing anomalies: Eliminate spots, strings. These defects in the tooth surfaces will cause the gears to mesh incorrectly.
• Other section settings: For example, higher nozzle temperatures will make the layers adhere better.
• Post-processing: 3D printed gears often require some post-processing to get them cleaned up and ready for use. You may need to use a knife to clean the teeth, and it's a good idea to sand parts with a file or sandpaper to remove inaccuracies and small blemishes.
• Annealing: Although not a setting you can change in your slicer, annealing is a post-processing technique that can make 3D prints function more like injection molded parts. By remelting the plastic, it is possible to make the part more homogeneous and have the same strength in all axes. This is particularly effective for PETG, although it can make PLA+ parts more brittle.

Most of the tips above apply to overall printer calibration. Alternatively, if you want to leave the printing to the professionals, you can try 3MG Bonev Ltd's 3D printing service.

Equip yourself

3D printed gears are feasible and can serve many different purposes. You can find inspiration and many examples of them on the Internet. One common application is 3D printing custom hobby gear like RC cars. It is also possible to 3D print gears for specific tools you are making. For its double gear carpentry vise.

Another common reason to 3D print gears is to repair broken parts. Gears that have been damaged by prolonged use can be repaired, keeping the intact parts of the component from the junk. For example, RWGresearch 3D printed a replacement gear for their motorcycle speedometer. There are even more applications for 3D printing gears, but these are some great examples of what's possible.

Regardless of the end use, we hope this guide has provided enough information to encourage and help you make these classic mechanical components.