Super Simple Belt Tensioner

by berky93, published

Super Simple Belt Tensioner by berky93 Sep 22, 2016
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Super simple belt tensioner for the Wanhao Duplicator i3 (and clones). Using this you can have easy-install and easy-tighten belts without the issues caused by the built-in spring tensioners. It's a quick print and works on both the X and Y axis.

In addition to the two printed parts, you'll need:

  • 1x M3 22mm bolt -- You could use a different length, but 22mm is what I used. Any longer and you'll have to either modify the model or hold it steady by hand while screwing in the first few mms until the guide grooves engage. Any shorter and you'll lose variable length and have to use a tighter initial state for the belts.
  • 1x M3 nut -- Nylocs are preferred to keep the belts from loosening.
  • (optional) small zip ties -- For managing the excess belt length.

Installation is super simple:

  1. Print both parts. I recommend using thick walls and dense infill for strength, since you really don't want these breaking mid-print. Even completely solid both parts print in only about half an hour so it's pretty easy anyway.
  2. Install the nut into Part 2. This can be a bit tricky as the slot is rather tight and the nut needs to be oriented such that two flat sides are parallel to the sides of the slot, meaning there will be a point facing upwards. I find the best way to go about this is to place the part on a table and use the thinnest pair of pliers you have to push the nut into place just far enough that it will stay. Then flip the part over and push it against the table to push the nut in farther. Finally, use a small tool -- the hex wrenches included with your printer work nicely -- to push the nut in all the way. Don't be afraid to use a little force. The nut needs to go all the way to the bottom of the slot and will generally "snap" into place. You can test to see if it's aligned by inserting your M3 bolt into the hole on the flat side.
  3. Install Part 2 on your printer. This process is simple. unscrew the right bolt holding your belt in place (check the pictures if you're unsure which one is correct) and then put the screw through Part 2 before replacing it.
  4. Insert the free end of your belt into Part 1. The existing loop of material in your belt isn't tight enough so cut the small zip ties off. Remove the spring tensioner (the thing that looks like part of a clothes pin) as well. We won't be needing that anymore. Pull the free end so there is no slack in the belt and take note of where it is roughly 3mm from the edge of Part 2. Remember, this is a tensioner so being exact isn't necessary. Form a loop at that part of the belt (remember to check the orientation) and insert it into the slot in Part 1. Use zip ties to neatly tuck away the excess belt if you desire.
  5. Insert the M3 bolt through the hole in Part 1 and into the nut in Part 2. Screw it in until your belt feels tight. This is where this print really shines. Not only can you fine-tune your belt tension, you can do so from the front of the printer. Of course, you'll need a flexible screwdriver extension to reach the Y-axis tensioner without flipping your printer over.

Print Settings


Wanhao Duplicator i3


Doesn't Matter




Something tough

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Just tried to fit this on the X axis of my i3 plus and it does not fit. Not enough clearance with the bearing block.

Unfortunately I don't have access to an 13 plus so I can't really do much to help with that. However, .step files are included for this part so it should be easy enough for someone to modify in a CAD program, should they desire to.

I'm looking to do a y axis extension mod soon to go to 300mm build area. This will involve setting up a longer Y belt and I have not done anything with belts previously. Would this be suitable to make the process simpler? Any installations tips for Y directions specifically? The mod in question is this: https://www.thingiverse.com/thing:1495689

Wanhao Duplicator i3 Y-Axis extension

Well, it might help a little. My tensioner mounts using the same screws and brackets as the stock belt so the process is fairly similar. However, due to its design you can mount the belt with less tension and then tighten, making it easier to install than trying to install a fully tight belt like you would with the stock tensioners. The screw-in design also gives you two different ways you can install the belt depending on which is easiest: with the tensioner fully assembled, pulling tight to insert the large bolt, or with the mounted half of the tensioner already in place, pulling tight to insert the small bolt to join the halves.

For those wondering, like me where finding a 22mm long screw, an M3 X 20mm screw works great!

top of the tensioner is rubbing slightly on the upper belt, the bottom side is being partially blocked by a screw below it

Which axis did you install the mod on? As for the belt rubbing, I haven't experienced that (though I admit the tolerance is pretty low -- there's not a lot of room to work with and I really didn't want to limit travel by extending the mount horizontally) but if you are having issues you could simply file the top down a bit with some sandpaper or a file.

printed belt loop and bolt hole facing up, need to slice a 0.5mm or 1.0mm off the top and make a small nick on the bottom for a perfect. It was printed at 100% scaling

Interesting. I never encountered any rubbing but I see why it could happen with such tight tolerances. Any variation in extrusion rate or printer setup could easily affect it, for sure. I don't think a little bit of belt rubbing will affect your prints, though -- there's actually a fix for older Duplicator i3 belt rubbing issues that uses a printed shim over the aluminum.

Comments deleted.

This really is a great design.
I'm having some troubles getting the nyloc into place, but that may be because of the 0.6 nozzle I'm using.

Still, the printer currently uses this tensioner, untensioned really, because the nyloc is too lose (printed too large) and I can't properly tighten the belt, but even though the belt is somewhat lose (only tightened when inserting it into the tensioner, which was pre-screwed together) the (small and slow) re-print of the nut-part is looking great. No wobbling, as I'm sure there'd be with the spring tensioning.

I'm glad you like it! As for the nylocs, they're intentionally very tight (since otherwise they might slip around when tightening). I find the best way to get one in is to hold it with a pair of needlenose pliers so that one point is facing down and push it into the hole as far as you can. Then use something like a screwdriver to push it the rest of the way. I've never tested it, but you could probably up-scale the model a tiny bit and then put some strong adhesive in the hole both before and after inserting the nut to lock it in place.

Dec 18, 2016 - Modified Dec 18, 2016
Rejutka - in reply to berky93

I tried that with the pliers/screwdriver - was too tight, so I ended up cutting the hole wider with Tinkercad.
(As I said, it's probably because of the 0.6 nozzle, so no big deal.)

Finally installed the tensioner on the Y axis. (Took me a while, there's a reason I bought a pre-assembled printer, instead of a kit :-D)

I also printed a second tensioner for the X axis - only to realize that because I still use the original (aluminum) bearings, there isn't enough room for that :-(

Do you think it would be possible to change the design so they fit in that tiny space? There's not much room overhead, and the belt is going back as well, so it shouldn't scrape. Maybe making it (way) longer?

The tensioner should fit fine on the X axis as-is. One of the photos above shows it in that configuration (I use it on both X and Y on my printer). The clearance above is very minimal but should be fine.

You're having a 2.1 I suppose? I've got a 2.0, different bearings: https://lh3.googleusercontent.com/-rl5m99-lr_8/VWXLBpi_YbI/AAAAAAAAB_Y/dicTqB1Zm4U/s400/DSC03026.JPG (didn't find a better picture, but you get the idea).

Oh, I see. My bad. Well, as noted in another comment thread, .step files are included which should allow you to import the pieces into any CAD program to modify. Perhaps you could combine this mod with one of the bearing block replacements? Would simplify your printer and lighten the load at the same time.

I have been looking at all of the belt tensioner designs and this one seems really well made.
Would you mind adding the .step file or inventor files?
I have my own x-carraige and I would like to incorporate it.

Sure thing. I'm glad you like it! I've added .STEP files. Enjoy!

Thanks man!

Comments deleted.

This one works on both the X and Y axis (note that the first and third photos are in different locations).