Can someone tell me what size thread the set screws are please in standard American format & also the size of the adjusting nut .
IE 10-32 or whatever it is, as the for the grub screws threads are impossible to identify, for the hole is cone shaped from misuse/ damage ( not mine I may add).
When I adjusted the taper roller bearing last week during the annual servicing of the lathe I realised one of the grub screws are missing , the one present was direct onto the thread . The grub screw itself is a very badly worn slotted head it took several light grinds on the grind stone to make a sharp cutting edge on the screw driver to extract it .
I think I'll try and get the new nut and turn it down as suggested , make a simple ring spanner on the lathe , weld a handle to it out of 1/2 " thick mild steel plate and tap it for putting in a small high tensile steel bolt as has been suggested & make some lead or Black Delrin seating plugs to fit the holes
On second thoughts ….. would it be possible to only turn off enough of the nut flats off to give clearance on the gear teeth & leave the rest of the hex nut in place so you can put a big bi hex spanner on it instead , drilling & tapping out the two locking grub screw holes as well ?