I know it's been a while but I have been holed up in my house for over a week now so I thought I'd post my latest project. I have posted similar items before, but nothing on this scale. It is a hybrid device that uses both bow arms and surgical tubing to get maximum velocity over a relatively short draw. Even so, this is one of the largest devices I have built, 20" draw length and 30" total length. You can see the many pieces it was assembled from here, I have to work within the size restrictions of my printer and the build plate (250mm x 210mm x 200mm).

No idea what to call this device, I think the technical term might be a sling-crossbow as it combines features of both (unlike a sling-bow it has a trigger and a locking mechanism so it can be loaded and then held at the ready without effort).

Pieces

Printing time was roughly 5 full days or 110 hours.

Unloaded

Early versions would flex far too much when fired, hurting the accuracy. So the underside was designed to provide additional stiffness, it also gives a good way to handle the device that keeps your hand well below the movement of the string (since this typically held like a rifle) -- one hand on the front or on the first foregrip.

Loaded with a 3D printed bolt

Here is the device loaded with a 3d printed dart, I haven't had a chance to fire it outdoors yet (all the places I would go are shut down) but my indoor testing clocks the dart at 120 to 150 ft/sec depending on the size of the dart. So that is at least starting to get into the low end of archery speeds, and possibly higher as more adjustments are made. The velocity can be decreased (or possibly increased) by adjusting the size of the spacers (yellow the photo) to set the pre-tension on the tubing. But as they are, I am running pretty close to the limits of the bow arms, which can fail if they are overflexed.

The original device that inspired it:

A small toy crossbow that the kids enjoy, used to play a re-creation of an old board game from the 80's where you built and destroyed castles using medieval siege equipment such as ballistas, catapults, etc. In this video you can see it destroying a wall made from loosely fitting 3D printed blocks.