1717's back in stock for a VERY limited time.

[brian015]

If you can use 14, 15, or 16t 6mm pinion, Kershaw Designs has them at a very reasonable price.

Otherwise I'd turn down the shaft to 5mm rather than attempt to drill out a pinion. Follow Neil's instructions:

Originally Posted by suicideneil

No worries, you can buy 6mm bore pinions, or you can just do like 99% of other guys did in your situation and grind the shaft down; all you need is padded vice and a metal file / dremel and some digital calipers. Stick the motor in a bag and poke the shaft through it to keep out the filings, then work back & forth along the shaft ( ahem.. ) and keep checking until your 5mm bore pinions fit snuggly. Either that, or sell your $70 motor for a large profit on a heli/ plane forum...

He doesn't say it explicitly, but you want to have the motor spinning while you hold the file up against it to turn it down - that should give you a perfectly round shaft.