If you have trouble making a new key hole in your old spring you may want to consider buying a used or new spring. Remember these springs from the Model 10's are around 70 years old. Some are now brittle and tend to break. Others are fine but become damaged due to mis-handling. Never let the spring "retract" without keeping it under control. The spring used in the Model 10's are the same spring used today in the Mark V and Mark 7. If you choose to buy a new spring from Shopsmith it only comes in the spring housing so it must be removed from that and installed in the Model 10 housing. It is part number 521875 and it is $33.37 + S/H. Good luck.
Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.