Bicycle Top Tube Storage Box (for B-RAIL)

I designed this box to fit me better than official B-RAIL boxes. It uses Official B-RAIL Mounting Rail for attachment to bike, which I find great for this purpose. The box can be easily removed and swapped for another accessory or taken with you when you make a stop during a ride.

It features a sturdy latch mechanism, which will not open on accident and is waterproof (when a seal is installed). 16 x 7.5cm (probably a bit larger) phone fits on the side.

Box main body, lid and a latch was printed from CF-PETG, regular PETG should be also fine. There is optional TPU liner / organizer to stop stored items from moving around and limit rattling. To save weight, I printed it with 0 walls and infill only, to create partially hollow finish (inspiration TPU wallet) 

Another optional part is a seal, can be directly printed from TPU or molded from silicone (model for a mold is included).

I molded mine seal from general purpose, neutral silicone from home center. I used vaseline thinned with mineral oil as mold release (worked better than PTFE spray). The key is push the silicone into the mold without creating pockets of air, which is a bit tricky. But usable result can be achieved if you are willing to experiment :)

TPU seal looks better, but silicone is more compressible and supple, so will work better as a seal. But box can be used without a seal.

3 metal pins are required, 2x 3mm diameter and 1x 2.5mm diameter, 35 - 40 mm in length.

Main box parts:

TPU liners and seal:

Location of pins:

TPU liners inside the box:

In case you decide to use a seal, push it into the groove

Comparison of different seal option with closed lid: