Fig. 69 shows an assembled frame in position in a frame-drilling jig.
Any errors in the frame are taken care of by the locations being made^self-
centring and compensating. Two Hammond double-arm drilling machines
cover all the holes, the machines being bolted on channel irons. Special
shanks are used for all the various drills to bring them to their correct levels,
and thus avoid vertical adjustments of the machines. The shanks are used
jn conjunction with quick-acting " Gronkvist" Swedish drill chucks, which
allow the drills to be removed without stopping the machine. The drilling