Place the blade-and-guard assembly against the antler handle to see where you need to drill the hole. Clamp the handle in a padded vise and, using a small bit, drill the hole for the tang. Enlarge the hole, using progressively larger bits, then finish excavating the slot with files until the tang and assembly fit into the hole. Don't worry if the tang fit is a little sloppy (it leaves more room for the glue), but make sure the blade-to-guard fit, and the guard-to-handle fit, are exact before proceeding further. Cement the tang in the slot using two-part 30-minute epoxy.