Even if you use best unibit (step drill bit), it will dull with use, so for best results, the tip and flute should be sharpened periodically.
Freehand Step Drill Bit Sharpening
If you don’t drill until the cutting edge becomes really bad, the appropriate results can be achieved just by regrinding the flute, and it is really easy to do with a coarse diamond hand lap. Sharpening step drill bits that are really bad would take forever, so keep them sharp, and the tool will cut nicely for a long time.
After a tough work, when you run too fast in hard material, the tool become completely dull, so you can’t perform unibits stepped drill bits sharpening without a power tool. One of the ways to do it is using a rotary bur. You just run the burr along the unibit cutting edge to make it square again.
Sharpening step drill bits with a bench grinder
It’s a step drill, not a close tolerance reamer. So yes, a step drill bit can be sharpened by the bench grinder wheel. 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 the 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 unibits till they become really bad, just regrind the flute, it’s really easy to do by hand with a coarse diamond grinding stone. It’s not the way to restore a really worn out one, because in this case it’s too time consuming task. But when it just starts to drill little worse than sharp, it’s very easy to keep the step drill bit cutting nicely for a very long time!
Using die grinder is also possible. But you should practice on cheap and dull bits to to get some skills. Special sharpening attachment makes the process much easier (see the video below)
Of course, setting the angle and grinding with a fixture looks nice, especially if you are a professional and work with step drill every day. But for me using a hand stone or diamond on the flute is enough.
Of course, the easiest way is to buy a new bit
If you are are wondering “can a step drill bit be sharpened?”, you have already appreciated the faster and more efficient drilling with it.
Consider the material you work with when choosing the bit. High-speed steel unibits are good for wood, plastic and sheet metal and titanium coating helps them to stay sharper a little longer. Carbide tipped step drill bits are more expensive but they are more durable, and cobalt tools are ideal for metals.
My advice is to buy HSS unibits of well-known brand and use them at at low speed and with cutting fluid. When the bit begins to cut worse, use diamond sharpener, do not drill until it overheats. And the bit will work for years and will save you a lot of time, effort and money.