Any unibit (step drill bit) dull with use, so for best results, the tip and flute should be sharpened periodically.
You can use special sharpening attachment (see the video below)
And the step drill bit can be sharpened with an ordinary bench grinder
Grasp shank firmly in one hand so you can rotate drill while supporting body with another hand.
Position drill tip at 45-degree angle to grinding wheel. Touch leading or cutting edge to a wheel. Maintain light contact while rotating drill clockwise, finishing at trailing edge. Follow factory contour as closely as possible. Trailing edge must be lower than leading edge by at least 1/32” to cut cleanly without rubbing.
If tip breaks, or if repeated sharpening grinds away first step, a new tip can be created by following above instructions.
Flutes can be easily sharpened with a proper sharpening stone. Grind cutting edge side of the flute to match factory contour in relation to the centerline of the drill.
If you don’t use them till there really bad I have had great luck just regrinding the flute, it’s really easy to do freehand with a coarse diamond hand lap. It’s not the way to restore a really bad one, would take forever, but when it just seems to be a little worse than sharp, it’s easy to keep em cutting nicely for a very very long time with just occasional lappings!
But the easiest way is to buy a new one, when using at low speed and with cutting fluid it will last long