Ender 3 Pro Y tensioner and extender

I am using a toolhead that moves the hotend forward a little, causing me to lose about 7mm of print space at the back of the bed.  I created this tensioner to allow the bed to move forward by an extra 15mm compared to stock in order to reclaim that space. There is a slight “bump” when the wheels go from the aluminum extrusion to the printed extension. This would probably create print artefacts, but it should be fine if the back 7mm of the plate is only used for skirts/brims. On a stock printer, this extension could allow the nozzle to reach behind the bed, for example for a cleaning brush or nozzle probe.

Required hardware:

1. M5x20mm countersunk screw and nut
2. Toothed idler pulley, 18mm diameter, 8.5mm width, 3mm bore
3. M3x20mm screw and nut
4. Stock M4 screws for mounting onto the 4040 extrusion
5. Longer belt

Notes:

1. On my printer (and on this model) the mounting holes for the Y tensioner are located 5mm and 15mm from the end of the extrusion. This is different than the Ender 3 Pro STEP file from Creality, so I'm not sure whether other units may have the holes placed differently. You can remix the model or use T-nuts to install the tensioner if the holes don't line up.
2. I adjusted the profile of the extension to match my 4040 extrusion as closely as possible, which resulted in the surfaces on which the wheels travel being offset by about 0.2mm outwards compared to the Creality STEP file. I'm not sure whether this is the same on all units.