I designed this strongbox as a project for the kids to assemble and "work on" with plastic tools. I used 123D Design and Tinkercad to complete the design.
There are two Zip files that contain the appropriate STL files – one for a large strongbox that is 280 mm long and one for a small one that is 160 mm long. The files are also listed individually. The large strongbox size (280 mm) was selected to fit within the limits of an FLSUN i3 (300x300x420) printer. I scaled down the large strongbox using Tinkercad to produce the small (160 mm) strongbox design for printing on smaller build volume printers. I have only printed the large strongbox, but the small one should print just as well.
I included a design for a small wrench to tighten and loosen the bolts. If you use the wrench, make sure you avoid over tightening and twisting off the bolt heads. The bolt heads are roughly 20 mm across the flats - the wrench is about 22 mm to provide a loose fit. The wrench was designed using Tinkercad.
The bolts and nuts used in this project were designed using NUT JOB – Nut, Bolt, Washer and Threaded Rod Factory by mike_mattala (www.thingiverse.com/thing:193647). An exploded view assembly drawing is provided to show how the parts fit together. Each strongbox requires a total of 27 bolts:
20 – 17x11mm bolts for the top, bottom, ends, and front corners
6 – 20x11mm bolts for the back hinges
1 – 25x11mm bolt for the front hasp
The bolts, hinges, connectors, and end pieces are the same size for both the large and small strongbox designs. All hinges should be printed with the narrow edge against the build plate and using a 3 mm brim. I found this worked better when cutting away support material to enable the hinges to rotate. Be careful when cleaning up the hinges to avoid breakage.
FLSUN Pursa RepRap i3 CPlus and HICTOP DC11
Bolts and hinges should be printed with at least 35% infill. The front, ends, and back can be printed with 20% infill. The Right, Left, and Center Connectors should be printed with at least 30% infill. The Top should be printed with at least 25% infill.