Hole drilling problem

On or around 20 Mar 2007 02:19:10 -0700, "Anzaniste" enlightened us thusly:

drills are bastards. 3-flute ones make better holes, but not that good, especially in thin material, and they need a pilot hole and are more of a tart to sharpen correctly.

Mind, make sure your brand new drill *is* sharpened correctly - I had a brand-new 20mm one the other day which was so badly sharpened that it drilled a hole about 21mm. mind, it wasn't the best quality.

for accurate fit, you need a reamer.

which brings me neatly to something I was wondering... I've got a 20mm reamer, to get accurately round 20mm holes. How much material is it reasonable to expect a reamer to take out? Obviously, the hole you start with has to be under 20mm (in this case), otherwise the reamer doesn't do anything, but how much is acceptable?

"Austin Shackles" wrote in message news: snipped-for-privacy@4ax.com...

About 10 thou for a reamer that size. It isn't very critical as long as there's enough material for the reamer to cut rather than just rub. You could probably get away with less if the hole is accurately drilled or double drilled.

Nothing went 'wrong'. It's a drill not a precision tool. It isn't meant to cut to an exact tolerance. That's what a reamer's for. Also all drills tend to wander about a bit. If you really needed a true straight hole to an exact size you should have drilled to about 0.25mm under and reamed to size.

steel

drills tend

Or he could have bored it in his vertical mill as it was already set up

AWEM

Much harder to work to a tolerance though, especially a small hole that long and a lot slower than drilling and reaming.