I prefer to fit the wheel to the axle before drilling for the taper pin. My jig is illustrated below, a simple piece of brass faced off at 31.25 (S7 BB) with a reamed 3/16" hole. I usually press one axle end on in the lathe completely and just start the other until almost through the wheel face. Both are put in the jig and the 2nd pressed fully home. This ensures that the two parts of the axle touch in the middle with the wheels at the correct BB. If you make the axle slightly over length it is easily faced of and centre popped leaving it flush or slightly proud of the wheel face depending on prototype. To quarter I drill through the crankpin hole in each wheel at the appropriate quartering and throw for each wheelset. A pin each side then locates the wheel ready for drilling. Nothing seems to be standard on the locos I build, hence the plethora of holes on the end, hence there is another blank made ready for the next set of wheels. There are also a number of differing positions for the taper pin depending on whether the gearbox gets in the way or not. Ian.