Y Axis Belt Tensioner for 40x40mm Aluminium Extrusion (Ender 3 Pro)

Y Axis Belt Tensioner for 40x40mm Aluminium Extrusion as used on the Ender 3 Pro

This came about after I replaced the Y axis rail that came with the ctc a13 (ender 3 clone), with the rail from an ender 3 pro. I didn't have the belt tensioner for it and since other printed belt tensioners I tried had failed, this is what I came up with. So far it's solid as a rock.

Comes as 2 parts, the main tensioner block and the optional faceplate which attaches to the end of the extrusion.
You can use either the 4x m5 nuts to adjust the tension of the belt OR a stack of m5 wshers (or other spacer) to leave a fixed gap (or no gap) between the tensioner and the faceplate.

To adjust the gap, simply loosen (anticlockwise) the m5 bolts, then tighten the nuts(anticlockwise) to increase the gap, or loosen (clockwise) to reduce the gap. Then tighten the bolts. Use a spanner to prevent the nuts from turning with the bolts.

The gap for the pully is 10mm, which is a very tight fit. I have included both 10mm and 10.5mm gap versions.

The original version 1 uses 2x standard upper bolts and 2x countersunk lower bolts, because that's what I had when I designed it.
Version 1.1 moves the top bolts back a bit.
The "all countersunk" versions replace the upper 2x bolts, with countersunk bolts
The "No Countersunk" versions replace the lower 2x bolts with standard bolts

All of the above versions come in 4mm and 5mm Idler Pully Inner Bore versions. There are a total of 16 versions of the tensioner block to chose from depending on your preference / parts available.

The faceplate comes in two versions:
v1a WITHOUT m5 washer recesses
v1b WITH m5 washer recesses

Also, the plate might need a little "pursuading" with a hammer to fit the end of the extrusion. It's intentionally tight to provide a solid fit. As are the recesses for the 4-8x m5 washers either side of the adjustmemnt nuts.

All washers are assumed to be 10mm in outer diameter or smaller.

Requires:
2x 30-35mm m5 bolts (upper holes)
2x 20-25mm m5 Bolts (lower holes)
4x m5 nuts OR stacks of m5 washers OR nothing for no gap
1x 40-45mm m4/m5 bolt (Idler)
1x m4/m5 nut (ideally nylock)
4x 10mm diameter m5 washers (recessed in the main idler block)
1x 10mm wide GT2 idler for 6mm belt width. Either 4mm or 5mm inner bore diameter. Will accomodate a 24 tooth GT2 idler.

Optional:
4x m5 washers (recessed in the the faceplate)
2-4x m5 washers (between the pully block and the head of the bolts)
2x m4 washers for the pully axle bolt and nut

Material: PLA
Layer Height: 0.2mm
Perimeter Walls: 3
Top/Bottom Layers: 5
Infill: >70% (needs to be strong)
Supports?: Yes

Print both parts, adjustment-nut side, down. Support the washer recesses, the pully cavity and probably the m4/m5 holes on either side of the pully.