Stephen used his keyboard to write :
Hello,

I tried to drill a hole through a 500mm concrete wall yesterday. I was
hoping to put a 15mm copper pipe through to an outdoor tap (you may
remember my other thread about the old pipe freezing and bursting).

I was unsuccessful. I used an sds drill and I got through the wall
quick enough but although I (thought I) held the drill level, the exit
hole and the entry hole were at two different heights and passing a
pipe through was impossible.

Now that I know from the "one metre drill bits at Aldi" thread that
these bits are flexible, is it possible that the bit deflected inside
the wall?

How can I prevent this in the future? I drilled from one side straight
through. Should I have carefully marked each side and drilled from
each side, hopefully meeting halfway?

For drilling though brick I have used a 16mm bit for 15mm pipe in the
past. Do I need to use something bigger than 16mm in concrete to allow
for it not being straight?

The hole diameter needed to be larger, as others have said to allow the
pipe to be sleeved and to give the clearance to be able to get your
pipe through. Something like a round bit of wood with an out facing
pointy end, put in the pipe end - would help to align the pipe to the
second part of the hole.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk