I played around a bit. 1 ingot of metal makes a boss and a couple of other small pieces. 2 ingots (and 3 ingots as well) makes the ring to the shield, but I couldn't figure out how to make the main part of the shield.
Entire Logs must be placed onto the Carpentry station located across from the furnace/smelter. - then a menu will pop up to select type of shield (OR CRATE, which is awesome) - This menu looks reminiscent of a vr ui or Chat bubbles that the npcs deploy.
Then you make a 2 ingot frame (3 ingot should be disabled) which you can cycle through till you match it to the wood part
Then you make a single ingot (3 times) until you have a boss, arm, and hand attachments- all in the same metal tier as the frame
Wood -> rim/frame -> boss -> arm -> hand (assumed order, may be totally irrelevant)