Yesterday i needed an M8 tap. When i was at the shop, i was thinking to myself, that this single tap, (cheap quality) would be lost or broken very soon. I ended up buying an M3 upto M12 tapping and cutting set, in a very nice suitcase so i can directly see when something is missing. (and yell at any person who failed to return it after use)

Price was 210 euro, but i said it was too expensive for my likings, as i came into the shop to buy just a single tap.. Shop supervisor then said he could give me 10% discount, or a price of 185 Euro. Then i replied " you know, SPENDING money is what people do in the pub. Buying lifetime quality tools, is INVESTING it."
I think he liked what he heard, as he promptly gave me another 5 Euro rebate by saying he'll sell it for 180...
Anyways, back on topic: I needed the tap to cut a threaded hole onto the sprockets of the street sweep i'm building, i cut off the shafts, and lost the ends with the keyways. I simply drilled and tapped an M10x30 bolt into each sprocket/shaft, in axial direction. This way it functions just like an official shaft key, only my version is round and threaded, so i dont need a mill and a broach to cut keyways
drawback is that you can only attach a sprocket to a shaft with this method, when the sprocket is on the very end of the shaft.