I don't keep a complete set of letter drill bits and odds are that I won't have the right number bit that I need to tap a hole at 11:00 at night. So here is a chart that gives decimal and fractional equivalents. Keep in mind that the fractional bits may be a little under or oversized for a given tap but the work well enough for general work.

Where?

A lot of industrial suppliers give tapping charts-tap drill charts away for free as advertisements. We have several throughout the shop. I also have several plastic tap drill cards in various tool boxes.

I often buy extra drill bits of the tap drill sizes when I buy taps. The only thing worse than a dull drill bit is searching the shop to find one. Most people have a drill index with half the drills missing usually because they broke the one they needed then the one that was close then the one that was almost big enough. When you are at the INDUSTRIAL supplier ask them for a chart.

you can tap at 65% without a problem and as low as 50% thread in some of the harder alloys. Also machinery's handbook has all that info and much more

My tap and die set has the chart on the inside of the cover as do the taps and dies individually. Some of the oft used taps have the drill size worn off.

Frosty the Lucky.

The only thing worse than a dull drill bit is searching the shop to find one. Most people have a drill index with half the drills missing usually because they broke the one they needed then the one that was close then the one that was almost big enough.

Anyone else here use a Drill Doctor? I think they're great. I keep several drill organizers full of sharp bits. If the first one is dull then grab the backup and put the first one in the 'to be sharpened' pile.

By my drill press I have all of my drill "stuff" which includes my steel bits & wood bits in an organizer, portable drills, battery drills and other assorted goodies. I also keep a row of Plastic peanut butter jars labeled on top and side with sizes of most used taps with their drills and an assortment of bolts that all fit together. It has just been a time saver for me to have it all in one spot. Tap drill charts are great but IMHO when I can grab the jar and have it all, it's just to simple. If I was a big shop I might do it different. I usually only use about 8 sizes regularly.

I used a drill doctor to the point where it was worn out. Not the wheels, I replaced them a couple of times. The plastic parts just wore out. I replaced the smaller chuck once but eventually the alinement sections gave it up. I still loved that tool and found it useful enough to not even think twice about buying another one. It continues to pay for itself in bit savings. But to be honest I do drill a lot of holes in a year.

When I sharpen old drill bits I get them close at the grinder and then make the final cut in the Drill Doctor. Saves wear on the Drill Doctor wheels. Drill bits have varying angles ground into them. I try to at least match that angle to the DD and get close to sharp while at the grinder. That way it just takes a few turns in the DD to finish up.