The ISO 702-2 norm for the spindle nose has incredibly tight tolerances. Only 0.008mm (three tenths for fans of a base 12 system) tolerance field on the major diameter of the taper, which is a point in space you can't actually measure. I had a thread discussion on this, and the way to gauge it is supposed to be a air gauge, but that will be just as difficult to machine accurately.
google "iso 702 download" there is link halfway down the page to a pdf download here on madmodder.
Thanks Mark, I did that, looking at the document I do see what you mean. However, I think that if one were making a spindle nose from stock, you'd cut the major diameter to dimension, then set the cross slide over & cut the taper REALLY carefully, sneaking up on the final dimension until the cutter just about brushes the final diameter. Then you'd cut the pictured reliefs in.
Also, looking at that diagram, I think I'd be making a size 5 nose, which gives me a whopping +0.01mm /-0mm tolerance; so as long as I leave it a "gnat's todger" oversized, I'll be golden. Of course, whether I can actually turn anything to these sort of tolerances on a worn out 1950s lathe with wobbly chucks remains to be seen!
Matt - Interesting! I've having my chuck jaws ground before (John Bogs gave it a go on his surface grinder, some years ago), which unfortunately made no difference to the parallelism; which suggests the wear is in the scroll. Your technique would certainly give me accuracy at the given diameter, but given the scroll is obviously worn wonky (there's a tight spot at around 1.75" ish as well, which adds weight to this theory), I'd need to make a set of those for every diameter I ever wanted to cut accurately, and I'd soon run out of jaw! I could convert these from hard to soft jaws, of course, but it's all starting to sound like a lot of work every time I want to use the machine.... The camlock nose adapter sounds like a hell of a lot of really quite complex work too, but at least it's a one-off project which - done right - will give me accuracy for years to come... Well, maybe...
I'm a long way off starting this project yet... I need some more tooling & in particular some of those rather excellent "ultra sharp" inserts that Chronos/Glanze do. They're supposed to be for aluminium but I use them for pretty much everything these days
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