[Unofficial] LowRider 4 CNC: HIDDEN BELTS MOD - Hide/protect wheel side Y axis belt inside metal strut / unistrut / superstrut (v2.0)

Only for LowRiders that are riding on metal strut (unistrut / superstrut). This mod moves the long axis belt (on the wheel side, not the rail side) down inside the metal strut, which both hides and protects it. In my case, this also makes it easier to load material as I don't have to disengage the belt to do so. 

Note on pics: the sharp looking blue LR4 in the pics is a make by fellow V1E maker Ty Paff - @TyPaff_3138536. Thanks for the pics!

The belt move is accomplished by adding a new, printed stepper motor mount, which allows the stepper to be installed while the toothed pulley gear is already attached. The new mount attaches to the LR4 side assembly by inserting the top of the new mount into the place where the stepper motor used to be! 

The mod also provides:

• new belt mounts and new belt tensioners (allows tensioning adjustments on both front and rear of the machine)

• new end stop, which is adjustable (currently, I think it only supports homing to the front of the machine, i.e. supports homing to Y-min. If you need to home to Y-max, then a remix of the far, rear endcap part will be needed, I think.

While this mod is for the wheel side (aka non-rail side), for the rail side to be attached to metal strut, you can use my “table extenders, rail clips, and rail placement jig v1.0” available at: https://www.printables.com/model/1178649-unofficial-lowrider-v4-diy-cnc-for-use-with-unistr  

NOTES

There was a version of this mod for LowRider v3, and it worked great for me for a long time and many jobs. See that listing here: https://www.printables.com/model/422468-lowrider-3-cnc-hidden-belts-mod-hideprotect-either 

In the attached photos of my unit, please consider that my own full-size LR4 is deviated from normal default in several ways, namely:

• Mine is mirrored, which puts my rail side and wheel side (non-rail side) opposite from normal

• Mine has X and Y axis swapped, aka as though my full-size table is rotated.

• And, obviously, mine has the hidden belt mod on the wheel side. 

Also note, this basic approach was initially conceived and designed during late 2024 and early 2025, although not finalized until late 2025.

HELPFUL TOOL

It really, really helps if you have a set of nice, long allen key drivers such as this one (Amazon affiliate link): https://amzn.to/3JVuYJM — in fact, at least one step cannot be done without a long reach allen key.

EKLIND 55166 Cushion Grip Hex T-Key allen wrench - 6pc set Metric MM sizes 2-6 (6In shaft)

Note: I designed a real nice holder for the above set: 

INSTALLATION

• Disengage your wheel side belt on the long axis. Remove the original, stock, printed tensioner parts/end-lock parts. Save the M3 screws that got used for locking in the belt loops — for reuse in the new setup.

• Remove the belt from the side assembly. Save for reuse.

• Disconnect wiring for long-axis stepper motor on wheel side, from your control board, and fish the wiring out so you can work with it. TAKE NOTE OF HOW IT IS ATTACHED, and bear in mind that it will need to be flipped 180 degrees later, because the stepper will get flipped around! 

• Prop up gantry, and disconnect the side assembly (on the wheel side) from the machine. Three M5 screws and M5 nylock nuts. Save the hardware for reattaching later.

• Remove the two smooth pulleys from the side assembly. Save them for use in the new mount (but different screws will be needed).

• Remove the limit switch. Disconnect switch from its wiring so you can fish out the wiring from the “final” terminal-end wiring tunnel of the side assembly. The wiring will eventually go from the bottom of the side assembly over to the new mount.

• Remove the front wheel well, and the stepper motor.

• [If I'm missing any steps, please let me know!]

• Prep the new printed stepper motor mount (part name: "LR4 Hidden Belts Mod, Wheel Side") 

  • Insert four M3 nylock nuts into the four capture slots. They will show a hex ridge facing out dead center when inserted correctly.
    
    

    

     

    • CONFESSION: currently the design only allows for use of three of them, due to lack of access, sorry. These nuts allow the new mount's printed upper part to “replace” the stepper motor in the original LR4's side assembly (later step!), and to thus be attached to it by the way the stepper motor used to be held in, with the exact same length of M3 screws.

  • Install the stepper motor into the new printed mount. Attach it with four M3 screws, from the bottom, exact same length as the screws originally holding it before. No need to remove the teethed pulley!

  • I think I delayed install of the limit switch until after I had installed the new mount into the side assembly.

  • Run/route the stepper wiring up through the new printed mount, feed it back into the side assembly for reconnecting it to the board, leaving some slack until the mount is installed soon.

  • Insert the two smooth pulleys, and pin them in place with flush-mount, aka "flat-head", M5 screws that are exactly 20 mm in length. These are to simply “self thread” into the printed part, and there are no nuts needed. Gravity will help hold them in place even. There is not room for nuts because the side groove opening in the metal strut does not allow enough space. If the flush-mount, aka "flat-head", screws don't sit flush with the printed part, then remove them and sand or grind their heads down a bit, and reinstall. It's very important that the 20 mm tall printed part (and the 20mm screws holding the pulleys), all be able to roll back and forth in the final assembly while making no contact with the metal struts. VERY IMPORTANT. NO TOUCHY! 

• Install the new printed mount into the side assembly. It should be a tight, snug, “press fit.” Take the slack out of the wiring as you do, and make sure the wiring is in the groove that's for it. Then use M3 screws (same length was what used to hold the stepper before), to lock it into the new mount. Again, limited access means only three of the four can be done, sorry. If any of you can sort out how to address that let me know. Three should be plenty good.

• Run the wiring for the limit switch as you see fit. There are several little holes/tunnels for either zip ties or the wiring itself! 

• Reattach the limit switch to its wires. 

• Install the limit switch.

• Run the belt into the newly positioned teethed pulley.

• Reattach the side assembly onto the gantry.

• Position the gantry in place on the machine, by first inserting the protrusion that will ride in the metal strut, then settling the rail side onto the rail.

• Using two M3 x 10mm screws and two M3 nylock nuts, install an "Adjustable End Stop" (shown below in red) as needed onto the correct “LR4 Tensioner Endcap” (shown below in dark gray) on the end where you'll be homing the machine. You can install an end stop on both but unless you have double limit switches for both Y-min and Y-max you only need one. 
  
  

  

  
   

• There is a single-layer thick “sacrifice layer” over the face of M5 screw hole in the “LR4 Tensioner Endcap” — this helps with printing, but now needs to be opened either by a drill, knife, or soldering iron. Open the M5 screw hole on both.

• Insert two M5 screws into the “LR4 Tensioner Endcap” parts - one tensioner screw in each. Can use either M5 x 30 mm or M5 x 45 mm, whatever you have. The longer the screw, the easier it is to catch the tensioner part later.    

• Install the two “LR4 Tensioner Endcap” pieces into your metal struts. They just slide in. If the fit is tight, tap with a rubber mallet. The set of two are mirrored from each other, and can work on either side of the machine. The part names/file names say “right” simply because on my table they are on the right side, but they will work on the left side, just flip the set around.

• Insert an M5 nylock nut into both of the “Tensioner Belt Clip” parts. If they are falling out, may a tiny dab of rubber cement or even CA glue after inserting them. 

• Install the “Tensioner Belt Clip” parts onto both ends of the belt. The set of two are mirrored from each other, and can work on either side of the machine. Push the belt through, loop it back on itself, and push the meshed double thick part back down into the slot. Just before the loop gets pulled in, put the M3 screw into it as a pin to keep it from being pulled all the way through. This is exactly the same as how belts get attached on LR4 elsewhere.

• On each end, reach in with the belt and tensioner clip, slide the clip into the endcap's groove, and catch the captured nut with your tensioner screw. Tension as needed.

• Whenever you get all tensioned, and buttoned up, and ready to test, have your hand on the power while homing for the first time, to power it down if your stepper is headed the wrong way. If it is moving the wrong direction, simply pull the stepper wire off the control board, flip it, and reconnect it!

• [If I'm missing any steps, please let me know!]

FAQ

• Q: Why only for the non-rail side? 

• A: Two reasons primarily:
  
  One is to preserve the LowRider method for failing gracefully if the bit should get caught immovable. Imagine that the non-rail side is the free moving side and the rail side is what is trapped. The non-rail side continues to move and the rail side then does a helical climb in place on the rail. Bottom line is the rail side needs to move upward as it does the twist. Now flip it. Imagine the non-rail side is what is stuck, and the rail side is still free moving. It will still need to spin and pivot up off the rail as a continuous forward or backward motion. Again we see that the bottom line is that either way it needs to be able to do a helical twist upward off the rail. If you have a plastic printed part protruding inside the opening in the unistrut on the rail side, it will prevent that upward movement. Note: This is not a problem at all on the non-rail side.
  
  Another reason is that if you have only one side hidden, it is still super easy to remove the gantry if needed. If both sides are captive inside the unistruts then you can only remove the gantry by sliding it all the way to the end of the table, and then sliding out the ends of the unistruts, and this would require first removing both of the belt tensioner / endstops at the ends of the unistruts.

Photos of my setup

Remember, mine is mirrored and my X and Y axes are flipped!

Change log:

• Nov. 21, 2025 - orientation corrected on some STL files. The .3MF files had correct orientation but some STLs were outputted without the correct side down. 

• Nov. 19, 2025 - initial upload of v2.0 (v1.0 designation is for my older version made for LowRider v3). 

Only for LowRiders riding on metal strut (unistrut / superstrut). Moves long axis belt (on wheel side, not rail side) down inside the metal strut. Accomplished by adding new stepper motor mount, new belt mounts/tensioners, and new end stops, which are adjustable. For the rail side, use my “table extenders, rail clips, and rail placement jig v1.0” available at: https://www.printables.com/model/1178649-unofficial-lowrider-v4-diy-cnc-for-use-with-unistr 

Change log:

• Nov. 21, 2025 - orientation corrected on some STL files. The .3MF files had correct orientation but some STLs were outputted without the correct side down. 
• Nov. 19, 2025 - initial upload of v2.0 (v1.0 designation is for my older version made for LowRider v3)