Updates

11/09/23 Added FoxguardV2 - stem-bkt.stl (32mm to suit other bikes, older bracket was 30mm). Added link to my new front splashguard here:
[https://www.thingiverse.com/thing:6211522]

23/12/20 "Part Foxguard V2 - mudguard.stl"
Strengthened the mid bracket mounting point since V1 snapped after I sat on it following a jump. Also reduced the wall thickness from 2mm to 1.2mm so V2 is lighter and much more bendy.

Description

This is my design for a rear mudguard that fixes to the 30mm seat post of a 1996 Muddy Fox Monarch mountain bike.

I tried printing the most common flexible mudguards on Thingiverse but felt that they did not stop enough of the water and spray that spatters onto my back. One of the problems with these mudguards is that they do not extend very far from the frame and another is that they can only be a tangent to the wheel since they must be bent to fit across the frame. I considered one of the types that fit under the saddle but I think that these could get in the way.

This mudguard is 260mm long and must be printed diagonally on printers like the Ender-3 which has a 250 x 250mm bed. The mid bracket is approximately 100mm from the seat-post stem bracket, so the whole assembly has a reasonable reach for maximum protection and it sits well below the level of the seat.

Ultimaker Cura slicer settings:
Wall thickness, top & bottom = 0.8mm.
Infill = 25% triangles.

The mudguard was placed diagonally on edge and sliced with 'Support overhang angle' set to 51 degrees to prevent excessive support generation.

I printed each item separately, using a 3mm brim to help the mudguard stay put and prevent the thin end of the mid bracket from warping. It's probably worth trying a lower percentage fill for the mudguard to make it lighter.

Final assembly:
One M4 x 12mm pan head screw is required to fix the mudguard to the mid bracket.
One M4 x 25mm pan head screw is required to fix the mid bracket to the stem bracket.
Two M4 x 25mm pan head screws are required to clamp the stem bracket to the seat post.
There is a provision for plain M4 nuts in each component but I found that the printed screw threads were adequate and nuts were not needed.