Step 4: Vambraces
I measured my wrist and my forearm for circumference and length. Then I drew a shape like a thin conic section to fit the measurements. On the CMS cardboard, though, I forgot to allow space to glue the vambraces together so I had to start over.
Note the diagonal scoring I did, again with the cap of a pen and the metal ruler. This allowed me to easily bend the cardboard into a conic section that would fit my arm, instead of a straight tube that would not.
If you have large hands compared to your wrists you may want to make the wrist area larger and maybe tape the vambraces to a pair of gloves to keep them on. In fact having worn these, I strongly recommend gloves! My writes got rather chafed on the edge of the cardboard.