On Sat, 07 Jul 2018 16:27:01 +0200, Emanuel Berg
wrote:

Are there any secrets to drilling holes in
steel bike frames? I have a couple of discarded
ones I can test on but I thought I'd
ask anyway.

Do you use normal power hand tools like
a drill-screwdriver and/or a drill press (if
possible with the desired bolt position)?

Use a drill press and a tubing drilling jig. I use one of these:
https://www.trick-tools.com/Center_It_Drill_Jig_CI_1_1154
I've had bad luck using an electric drill. A drill press (or vertical
mill) is best.

Do the normal rules apply, e.g. to get
a threaded hole for an M6, you first drill with
a 5.0mm drill?

The tubing is probably too thin for threading the hole. You need at
least 3 full threads wall thickness tubing to keep the mounting screw
from stripping the threads out of the hole. For an M5x0.8, that's 0.8
mm per thread. So, the minimum tubing wall thickness would be 2.4mm.
However, since the tubing on your bicycle is probably around 0.5mm
wall thickness, the tubing wall will never be thick enough to support
threading. To get more threads to grip is one reason why builders use
braze on bosses for mount points.

You should have a drill chart available. Print one and hang it
somewhe
https://www.google.com/search?q=tap+and+drill+chart&tbm=isch

And you can use chainsaw oil, right?

Maybe. High tack oil can be applied to the boss and left to harden
into a passable glue. In a few months, it should be sufficiently
hardened to support an empty water bottle for a few miles before it
falls off.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558