Generic Linear Actuator With Built-in Tension Spring





Introduction: Generic Linear Actuator With Built-in Tension Spring

1/24/2018 Update: The STL files have been updated with a stronger belt grip.

3/17/2018 Update: Added STL files for openBuilds 2020 rail.

After building the Cantilever printer (instructable here: I decided to design a more generic linear actuator. Unlike the cantilever printer the belt would run entirely on the inside of the aluminum extrusion. Unlike the cantilever printer that uses belt tensioner clips, this actuator will have a tension spring inside the idler end.

The current design has the electronic end stop build in to the NemaEnd. The STL files will have a Nema End without end stop holder

The design was created in Fusion 360 and can be downloaded from

The implementation in the attached video uses a nema 17 0.4A stepper and can reach 11000 mm/min before skipping. Adding a stronger stepper should get you more speed.

Step 1: Parts List

below is a list of all parts (non 3d printed) with Amazon links for download. I have to point out that shopping directly from China (i.e. AliExpress) could bring cost down.

8020 1003 series
Belt tensioner spring


stepper nema 17 0.4A

Linear Rail MGN12 250mm

Square nut

hex socket screws:

Idler 3mm bore:

2020 t-nut:

GT2 timing belt:

Step 2: Assembly

Once all parts are printed assembly speaks for itself.

Wire the End-stop prior to sliding into the Endstop case

Add Idler to Idler End with a 25mm hex socket screw

Add tension spring inside the Idler End and slide onto aluminum extrusion

Slide Nema End on opposite side of Aluminum extrusion

add nema stepper motor into Nema End but don't screw down yet as you will need to measure and attach belt

Wrap long piece of GT2 belt around idler and nema pully and mark were end meet at belt clip BUT before markign make sure there is tension on the spring (the spring is 20mm, I recommend pushing it in some 7-10mm when measuring belt).

Cut belt and insert ends into belt clip (meeting at the center)

remove nema stepper and loop belt all around the Aluminum extrusion.

Tension the spring which will leave enough room to push through the Nema Pully.

Screw down nema and release tension.

Step 3: Test Actuator

Once assembled you can test the actuator by connecting it to a RAMPS 1.4 setup connected to an application like Pronterface.

Make sure that the axis your using is configured within the boundaries of the actual actuator. You can configure the Marlin software accordingly.

In the video attached the Ramps is executing the print of a vase. The Linear Actuator represents the X-axis

Once you've build one or two of these connect them (with attached Slider Clamp) and have fun

If you liked this check out my other instructables or visit my website at

Step 4: Parts at Work

In case you're wondering what to do with it, check out this video



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    also which power supply do you suggest off amazon for something like this or your other printer?

    I had one burn out the other day and replaced it with this one Seems to be working well less than $20. If you're printer is going to be around kids you can go with a brick like this one : (not enough amps to heat bed though, I think)

    might just have to build this for my plotter conversion. if i can't get the original gantry to work, Ill replace it with this! thankfully the HP extrusion can be unbolted from the main superstructure. might need to do some minor fabrication of brackets that would allow this to be bolted on in its place. very good design, clean, and simple.