We needed black-out blinds for a loft window. The inclined nature of the window, being set into the roof of the house, would have necessitated expensive specialist blinds with guide rails or similar. Since the window was not of a standard size (i.e. not VELUX or similar due to the buildings age) most off-the-shelf blinds would not have worked.

I found a set of blinds which could be cut to the width of the window (simply using scissors and a junior hacksaw) and set about creating a catch for the bottom end of the blinds. The blinds we went for, Argos Blackout Roller Blinds £12.99 http://www.argos.co.uk/static/Product/partNumber/1896275.htm, have a pvc tube at the bottom with a rounded rectangular profile. I drew up a fitting in Fusion 360 to capture this profile with a pair of screw-holes to affix the fitting to the window frame.

3D print two of these fittings and fix them to the window frame (double-sided tape might be sufficient in some cases, I screwed them to the wooden frame). The blind is lowered and raised by a cord/chain and can maintain some tension on the blinds.

It doesn't block out all the light (see photo) but it makes a significant difference.

Ultimaker

Ultimaker 2

No

No

0.1 or 0.2mm

100%

Could be printed hollow but for all the time/material difference I went for a solid part.

Autodesk Fusion 360