I love packable bags, but the arm straps by nature are uncomfortable. A sternum strap seems to place the arm straps in a good location which makes the bag much more useful.
I designed 2 different sizes. A 7.5mm x 1.5 mm which fit my SeaToSummit Ultra-Sil Daypack and a 10 mm x 1.5 mm version which fits my 10L Ultra Compact Quechua bag.
The prints were made on an Ender 3 V2 with Overature PETG, printed with a .4mm nozzle on high quality (.12 mm). I reduced the temperature from 240C to 237C to reduce stringing and had to lower the nozzle a bit for a good first layer (I am usually printing .2mm layers). The Z-offset was changed from -2.54 to -2.62. I just kept lowering the Z-offset until I got a good first layer. It is worth the trouble to get a structurally sound part. Use 100% Infill. Print time is quick at 5 minutes for the smaller version and 10 minutes for the larger version. Ironing is recommended to make it pretty.
The parts won’t experience strong loads, but the parts are made to be a small and light as possible, so they are experiencing strong loads relative to their size. The parts for the 7.5 mm was sized up until the part was strong enough not to bend easily with the angle of the webbing.
Clean the parts up well with an exacto knife as the tolerances are low. If you are having trouble inserting the webbing, cut it so it inserts easier and use a small tool like a needle or micro screwdriver to push it through. Melt any frays after. Melting makes blobs which increase the size of the webbing. The tolerances, especially on the 7.5 mm version are tight so they won’t fall off in the field and hold adjustments well. Buckling the parts together the first time may take some effort, but things loosen up perfectly after.
The author marked this model as their own original creation.