I have read something similar ……may have been Tubal Cain…..where you drill the hole three or four sizes smaller then increase the drill size one size at a time until you reach the desired dimension. I have only used this once or twice and used metric drills in 0.1mm stages but did get a very good result. I don't think that it would be a good substitute for cylinder boring though

Mick

Yes I've done it more than once, you round off the 2 'sharp' corners to ensure there is less of a tendency to cut oversize.

Drill undersize & just take out a small amount with the final 'sizing' drill.

Tony

Another way I have finished hole sizes is to drill undersize then press a steel ball throught the hole.

Use an end mill that cuts straight. Choose one of the correct size. Better, than a twist drill in smaller sizes, any day. As above, if a bigger hole, bore it.

Hi chaps, have used the drill technique many times, in his youth my dad worked for a firm who made standard drill bushes to make up production if things were slow, in adult life I found myself in precisely the same position so he downloaded all his wizard wheezes to me, first drilling to size, stone outer corners to a visible radius, remember you are trying to turn the drill into a reamer, drill initial hole having centred the stock, peck drilling if needed, as you approach final size its permissible to bore a short distance to ensure a true start with your reamer/drill even if you have to face that bit off if finish is not up to scratch, remember you are reaming, slow speed coarse feed, got good results down to three sixteenths inch diameter this way, all specials for Catapillar Tractor Belgium. Had similar fun with larger headed sleeve type component that been peck drilled through, my second op. was to render the hole to size with a finish slightly better than one resembling a little dogs bottom, tool 3 flute core drill again with stoned corner rad. position tools, start 0.040" feed, chamfer bore after drill has started to cut, broadface flange, chamfer o/d, job done with mirror finish.

Finally, sizing machined bores with a large ball is called ball burnishing, used to get accurate size & fine finish when ie brass bushes have been pressed into bosses & flanges, end result precise size, fine finish, blink of an eye.

Cheers Bob.

Ray I was taught the same method. I was trained in a small jobbing toolmakers where invariably you did not have the right size reamer, and the job did not justify the cost of buying one let alone the time involved going and getting it. The advantage is with this method you will get a better finish than with a straight drilled hole, just remember to forget the old rule for reaming of half the speed and twice the feed, you are using a drill not a reamer. Just leave .005"/.010"to come out of the hole. It works every time.

If there are any Toolmakers or precision machinists still going it will be a well known dodge.

Tony