Externally Accessable Y axis belt tensioner for Taz 3-5 printers

One of the things I really enjoy tweaking on my 3d printers is belt tension. And it’s always bugged me that there was no really good way to adjust the belt tension on the fly since all the relevant parts are under the moving bed. I think I’ve solved that issue though, and all it took was a handful of parts and a new hole in a perfectly good plate.

Presenting: The long rumored but seldom posted Externally accessable Y axis bed tensioner of doom!

I wanted it to be easy to adjust, simple enough to install, wwork with my other modifications, and have a provision for mounting a Y maximum endstop. I think I have accomplished those goals.

The idler assembly now rides on the 4 1/4" threaded spacers, with an m4 bolt providing tension and adjustment. I will probably end up getting longer threaded bolts for the spacers and adding a washer on the end along with another nut to add “catestrophic bolt failure” insurance, but you get the general idea from the pictures. I’m still printing the new Bed belt mount wiht the Y maximum endstop target.

To install this:
Place the drill guide on the Idler end Y axis plate (prefferably with it dismounted from the machine) and hold in place with some stock M3 bolts and nuts from the stock Idler. Find a drillbit that fits the 4mm hole, drill it, then discard the spacer. You then insert 2 M2 heat set inserts into the Endstop holder (not pictured yet) and use threaded spacers and bolts to hold that part to the backside of the Y idler plate. Please note that the plate is directional, and you want the holes offset to the right with the assembly on the machine. Then you slide the new idler assembly over the pegs (some drilling to ensure smooth fit may be required) and insert the M4 lock nut in the hole and use the m4 bolt and washer to seat it. Then install the stock Lulabot idler hardware (m8 bolt and nut, 2 washers, 2 608zz bearings) and back the M4 bolt off a bit. you want to start with about a 12mm long m4 bolt and have at least 3mm worth of the spacers exposed to allow for tensioning. Then reinstall the plate and the belt getting it fairly tight. Now you can add additional tension by turning the M4 bolt. The belt will tend to self allign the idler assembly.

Not pictured: add a washer and a bolt on at least 2 of the 4, if not all of the spacer posts at the end.

As always, Open source Creative Commons: Attribution. If you want a different file format, just let me know. Thanks!
Belt Tensioner Drill Guide.stl (149 KB)
Belt Tensioner Z max Endstop.stl (79 KB)
Belt Tensioner Belt Mount 1_0_a.stl (72.4 KB)
Belt Tensioner Body.stl (127 KB)

Turns out I was overthinking the longer bolt thing. I just stuck shorter bolts with washers in the other side of the spacer instead. That should have enough holding power to keep things in place long enough to fix a catestrophic bolt issue.

More pictures