On Thu, 06 Feb 2020 19:31:35 -0000, "Commander Kinsey"
wrote:

On Thu, 06 Feb 2020 19:08:24 -0000, Ralph Mowery wrote:

In article , says...

On 2/6/2020 1:36 PM, Thomas wrote:
98mm is under 4 inches. What do you consider short?

Depends on size, thinner are shorter. You can find a few 18" ones here
https://www.mcmaster.com/extra-long-drill-bits




Just getting into this, at work we had some 1/8 inch bits and a few
other sizes up to about 1/2 inch that were about a foot long, some 1/4
and 5/16 inch bits that were about 5 feet long.

I bet those snapped easily.

Without a doubt, longer bits are often more vulnerable than shorter
ones in all sorts of situations, especially if the shank is the same
diameter all the way up.

Doing your drilling in a pillar drill with the job firmly held and
when taking it easy then it might be less of an issue but a longer
(especially thinner) bit can have more whip, less rigidity (especially
when first starting to drill) and more likely to snap if it binds as
there is less torsional rigidity to push the cutting face passed it's
stalled point (so the bit can 'wind up' more).

Using a long bit in a hand held drill is more difficult than a short
one (again, as a function of the diameter, specifically the smaller
diameters) as they would be more likely to get caught on stuff and
hence broken in general use (I've broken a brand new bit in a cordless
drill by just putting it down).

Also, because they are more flexible than shorter bits you can often
over flex them if trying to 'steer' the bit into the workpiece and
similar if you don't keep the drill parallel with the hole, once the
bit is in the workpiece (you don't get as much feedback because the
bit is more flexible than it's shorter counterpart).

I know I've been lucky if I'm able to put a longer / thinner bit back
in it's box after using it than I am a std / shorter one. Part of that
is because they are usually more expensive and secondly because they
aren't as easy to obtain as 'std' bits (so if you break the last one
before you have finished the job you could be stuck, even if the
hardware shops are open).

As an aside, I was surprised to snap a quality 13mm HSS bit whilst
drilling though some thinish steel the other day. I was in a hurry and
so pushing things faster than I might (like increasing the size of a
hole in more suitable increments) but was surprised it happened with a
cordless drill (Stanley Fatmax). [1]

Cheers, T i m

[1] I think I had the drill on the slower speed (more torque) because
of the amount of metal I was moving (and without coolant etc) and
because there was little rotary inertia, when the bit tip snagged it
twisted the drill sideways slightly causing a bending moment on the
drill shank and hence it snapping.