On Saturday, 27 May 2017 17:32:21 UTC+1, PeterC wrote:
On Sat, 27 May 2017 09:41:52 +0100, John Rumm wrote:

It's the hole into the side of the door that the latch body slides into,
not the one that the spindle goes through :-) I need to make it wider
and deeper to take a larger latch body.

Many years ago I had to do the same. Used a step drill to get the initial
diameter correct (only a few mm depth of course) then a spade bit the rest
of the way.
Looking at other comments in here, I reckon I was lucky to get away with it.
An auger-type bit would be less likely to bounce around, but might be too
viscious and pull in.

Augers tend to pull in due to the effect of the worm drive on the
front[1]. In this application that will be spinning in free space, and
so not having any effect.

[1] A common trick to "tame" an auger is to pre-drill with a smaller bit
such that you leave less or nothing for the worm to engage with.

I was thinking of the cutting edges 'picking up' the wood, rather like a HSS
bit does on plastic. At work we had a few backed-off bits, but doing that to
a 25mm auger is a bit expensive for 1 hole.

FWIW Bosch multiwotsits are already backed off, no alteration needed. It helps them survive the masonry busting action better.


NT