On 11/09/2015 13:39, stuart noble wrote:
On 11/09/2015 11:14, Tim Lamb wrote:
In message ,
goodolpete writes
On Monday, September 7, 2015 at 4:28:37 PM UTC+1, Richard Conway wrote:

Thanks for all replies.
Richard.
Bought these components from ToolStation. I will buy a
"PTX Bi-Metal Holesaw (Dia) 35mm" from B and Q.
I already have the central drill for this, but obviously
there is no material for the central drill to go through,
so the 35mm bit will just hit the plastic full on.
Have you or anyone any suggestions on how to make this a
successful operation, as I can see the drill slipping about
and making an even bigger hole in the side of the barrel.

IME hole saws tend to make an overlarge hole in thin material.

Often because the pilot drill flutes are trying to support the hole saw
teeth rather than the drill shank.

Perhaps you could wedge (hammer in) a roughly shaped plug to suit your
bodged hole and use that as a hole saw support.

Somewhere in my accumulated tool store I have a kit for creating holes
in plastic water tanks. After drilling a pilot hole you fit from inside
a threaded disc which is larger than the intended hole and has a
circular groove to match. An external threaded spigot secures this to
the tank side. The cutters are similar to a hole saw but with many fewer
teeth and, guided by the spigot, rotated by hand to cut the hole.


+1. It's what I used many moons ago. A doddle to use and not expensive,
but what the hell was it called?

Sounds like a q max cutter more usually used for punching holes in metal:

http://www.amazon.co.uk/Q-Max-Sheet-.../dp/B0055KJGW8