How to 3D Print a Moving Part in a Single Build

One of the most common questions I get from our customers is “How do I print a part that moves right out of the machine?”

My answer – it’s simple. It just takes knowing the calculations needed to separate the moving pieces of your design (which depends on the layer resolution of the printer you’re using) to make sure your final part is fully functional.

Follow along with the steps below to see how I accomplished this with a set of gears in a single part.

SOLIDWORKS — DESIGN YOUR MOVING PART

I’m using SolidWorks for this design.

1. In the SolidWorks Toolbox, select ANSI Inch>Power Transmission>Gears. Right click on spur gear and click “Create Part”
2. Now configure the gear how you want. You can use two of the same sized gear, or create two different sizes. The key is to make sure they have the same pitch and pressure angle. In my case, I have created a single gear with 15 teeth, a pitch of 6 and a pressure angle of 20.
3. Click the check box to create the part.
4. create a folder where you will save the rest of the parts and save this part to that folder.
5. Design the connector that will hold the gears. It will have a top and bottom, and two pegs on each end. This pegs should be sized a little bit smaller than the hole in the gears. In my case, my gear’s hole is .3125” in diameter, so my peg is .3” in diameter to give my gear ample clearance to spin freely.
6. We will also need to determine how far to space the gears apart. The calculation for center distance between two gears is (N1+N2)/2P where N is the number of teeth and P is the pitch. In my case this is (15+15)/(2*6) = 2.5”
7. Now that we have our gear(s) and connector designed, it’s time to create an assembly. Save the connector to the same folder where we saved the gear, then go up to the File menu and click “Make assembly from part”.
8. Insert the 3 components into the assembly – connector and the two gears. Make sure you insert the connector first because the first component you insert into the assembly is fixed in space by default.
9. Before the next step, you’ll need to calculate the needed distance between parts to ensure the parts will move. Every 3D printing technology and machine has its own parameters, so this will vary. In this case, we’re using a uPrint FDM printer so we will account for a gap of .010 inches – or one thousandth of an inch – which is the layer resolution we plan to use for this part.
10. Place the two gears on the housing and mate them together. Do this by creating an offset mate between the face of the gear and the face of the connector. Again, this offset should be set to the layer resolution of your printer (in this case, .010 inches).
11. After you mate the gears to the connector, you should be able to click on a gear and drag it to move it around the peg. If you want to double check the assembly to make sure the gears mesh properly, you can turn on physical dynamics to see how the gears interact with each other. This is really useful to determine if the gears are properly spaced because it will simulate if the gears jam or if there is too much play.
12. Once you are happy with your assembly, go to File > Save As and select STL from the dropdown menu. Make sure you click the options button and in the next window check the box to save the entire assembly as a single STL file to ensure your design will print as a single part!

If you’d like to try printing the moving gear part we created, download our SolidWorks Gear Assembly below below.

Download SolidWorks Gear Assembly

CATALYST SOFTWARE – TEST YOUR DESIGN BEFORE PRINTING

Although we are feeling confident that we spaced our part properly, it would be nice to be able to verify that the part will print as expected. This is where CatalystEX can help. Catalyst is the software that slices STLs into layers that the 3D printer can use. You can think of it as the driver for the 3D printer. It is very simple to use, but has a few extra features that many people aren’t aware of. One such feature is the ability to look through your part layer by layer before printing.

1. Open your part in Catalyst software.
2. Orient the part so that the face of the gears are parallel with the top plane.
3. On the orientation tab, click Process STL to create the layer slices.
4. You’ll notice that some of the orientation tools that existed before you processed the file have been replaced by layer view tools. Click the “Bottom” button to view the first layer.
5. Now press page up on your keyboard and hold it. This will cycle through each layer in the part. You can press page down to move back down and just tap them to move a single layer at a time.
6. The goal here is to make sure that there is one layer of support material between each individual part in the assembly. If you don’t see that layer of support, it means you probably got the gap incorrect in SolidWorks and your part will fuse together during the print. Although we are printing a simple part right now, there is nothing more frustrating than printing a 20 hour build to only find out it didn’t work the way you expected. This feature can help save you time, money and aggravation, so it is worth your time to learn how to use it!
7. Once you’ve verified your part will move, click Add to Pack on the Orientation tab, move to the Pack tab, position your part on the tray and click print.

Don’t have SolidWorks but still want to print our part? Download our gear assembly STL file below.

DownloadGear Assembly STL File

This type of part works really well when made on an FDM or PolyJet printer that utilizes a soluble support structures. Machines that only use a single material for both model and support will not work very well because it will be impossible to clear the support material out of the inaccessible areas of the model. Once the part is printed, simply place it in your cleaning system to dissolve the support material.

If you’re using a PolyJet printer, you’ll need to take extra consideration during the design process about how the support material will be removed. More tips on this can be found in the Stratasys 3D Printing Curriculum.

Let us know how your final part comes out. Good luck!