Tom Gardner wrote:
How did I ever live without this? In my little world, I have had to mark
and drill holes for bolts, threads and pins and have gotten lucky and not so
lucky. The mark of a good machinist is how well he RECOVERS from little
inaccuracies. My designs have always included fudge-factors for eyeballed
holes, as setting-up edgefinders and using the BP for drilling every hole is
just too time consuming and relies on accurate edges, good math and
back-lash problems. My thanks to the person that came up with the optical
center punch, it sure fills a spectrum of jobs. I think this should be one
of the first tools in a machinist's box!

If the base is accidentally moved between lining up the mark and
exchanging the optic rod for the centre punch, presumably you don't find
out until you've punched the wrong place? I guess people don't find this
a problem...

Chris