You could use this frequency counter, and paint 60 white marks on the lathe driver, that would give you a direct reading of rpm,
http://m.ebay.co.uk/itm/Crystal-Osc...-LED-PIC-DIY-Kits-Ho-/371445747930?nav=SEARCH
Its going to be a lot cheaper to buy a ready-made one.
http://m.ebay.co.uk/itm/Crystal-Osc...-LED-PIC-DIY-Kits-Ho-/371445747930?nav=SEARCH
Its going to be a lot cheaper to buy a ready-made one.