I am attempting to build an add-on for my lathe. Some decades ago I drilled and tapped some holes in the end of the bed. This was to extend the centre to centre dimension for a job. Now I want to reuse these holes for a different purpose, the question was, what are the relevant off sets to the leadscrew.

I poked a series of drill into the tapped 8mm holes and found that a 6.6mm went through but was a rattling fit, but 6.7 would not go in. The other hole was 6.9 and 6.8mm. A better plug had to be found!

I faced of a bit of 8mm studding, leaving a tiny pip on its centre. I then hacksawed a screwdriver slot across this face as close to the pip as possible.

So now I screwed both studs into the holes , put a piece of ali across them and tapped it with a hammer. Two perfect centre dots, bit easier to measure now. Poking a screwdriver into the offset slot allowed me to unscrew the studs.

Frank