On Sun, 16 Aug 2020 20:01:00 +0100, williamwright wrote:

Have you noticed, though, how the hammer action is less effective with a
heavy bit?

Is this a normal "hammer" drill or SDS?

Unless the substrate is pretty soft (ordinary brick/block) "hammer"
drills aren't very effective anyway.

With SDS if you don't apply enough pressure the bit just chatters in
the hole, barely making any progress. With enough pressure you get
that satisfying BRRRRUUPPP as the bit "engages" and you might be able
to back the pressure off a little as the bit sinks into the material.
In the former, the mass of the drill absorbs the energy of the
impacts as it rattles up and down the hole. With the latter you have
a Newtons Cradle effect and the impact energy just passes down the
drill with it's mass having very little effect as it's barely moving.

I used to have to drill through brick and stone walls very often, and I
found that if the material was hard and the hole was quite wide it was
quicker to drill as far as possible with a short bit, then change to a
longer one when necessary. The reduction in drilling efficiency when
changing from, say a 12mm x 150mm bit to a 12mm x 400mm.

Can't say I've noticed but then I'd normally start with a shorter and
probably smaller bit to start the hole simply because it's easier to
see the starting position and is easier to control. My long bits are
1000 mm though. B-)

--
Cheers
Dave.