The grand kids are coming for a holiday. I have a composition
material medicine cupboard with no lock. What is the best bit to use
the make a clean, 20mm cylindrical hole in the door?

I have a Forstner bit which I've used for some stopped housing jobs
but to go all the way through, wouldn't I need to drill a pilot hole
which has tended to cause loss of Forstner bit centering in the past.
Is there a more suitable bit?
--

Mike

On 21/07/2023 07:04, Mike Halmarack wrote:
> The grand kids are coming for a holiday. I have a composition
> material medicine cupboard with no lock. What is the best bit to use
> the make a clean, 20mm cylindrical hole in the door?
>
> I have a Forstner bit which I've used for some stopped housing jobs
> but to go all the way through, wouldn't I need to drill a pilot hole
> which has tended to cause loss of Forstner bit centering in the past.
> Is there a more suitable bit?

The Forstner bit has its own centering tab so no pilot hole is needed.

You will need to securely clamp a piece of scrap wood to side of the
door that the bit exits so that you don't get breakout and to give
something for the Forstner bit centering tab to bite into for the last
5/10mm of the cut.

Consider the clamped bit of scrap wood as just making the door thicker
so effectively you are not drilling through the complete thickness of
this combined material.

The above assumes that what you are drilling through is not hollow
beneath the door skin.

Probably put some masking tape on the front surface of the door which
may/will prevent cosmetic damage when drilling.

If you can use a stand drill you stand a better chance of keeping the
hole 90 degrees to the door front.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Friday, July 21, 2023 at 7:22:58 AM UTC+1, alan_m wrote:
> On 21/07/2023 07:04, Mike Halmarack wrote:
> > The grand kids are coming for a holiday. I have a composition
> > material medicine cupboard with no lock. What is the best bit to use
> > the make a clean, 20mm cylindrical hole in the door?
> >
> > I have a Forstner bit which I've used for some stopped housing jobs
> > but to go all the way through, wouldn't I need to drill a pilot hole
> > which has tended to cause loss of Forstner bit centering in the past.
> > Is there a more suitable bit?
> The Forstner bit has its own centering tab so no pilot hole is needed.
>
> You will need to securely clamp a piece of scrap wood to side of the
> door that the bit exits so that you don't get breakout and to give
> something for the Forstner bit centering tab to bite into for the last
> 5/10mm of the cut.
>
> Consider the clamped bit of scrap wood as just making the door thicker
> so effectively you are not drilling through the complete thickness of
> this combined material.
>
> The above assumes that what you are drilling through is not hollow
> beneath the door skin.
>
> Probably put some masking tape on the front surface of the door which
> may/will prevent cosmetic damage when drilling.
>
> If you can use a stand drill you stand a better chance of keeping the
> hole 90 degrees to the door front.
>
>
> --
> mailto : news {at} admac {dot} myzen {dot} co {dot} uk

An alternative to clamping a back piece is to drill slowly and carefully. As soon as the tip of the forstner appears stop drilling and start drilling fom the othe side

Mike Halmarack <mikehalmarack@gmail.com> wrote:
> The grand kids are coming for a holiday. I have a composition
> material medicine cupboard with no lock. What is the best bit to use
> the make a clean, 20mm cylindrical hole in the door?
>
> I have a Forstner bit which I've used for some stopped housing jobs
> but to go all the way through, wouldn't I need to drill a pilot hole
> which has tended to cause loss of Forstner bit centering in the past.
> Is there a more suitable bit?

An Auger would produce a clean hole with a scrap piece clamped to the back.
The beauty of Augers is that having a lead screw as the drill breaks
through the lead screw tends to pull the scrap piece tight onto the back of
the piece being drilled.

Richard

On 21/07/2023 07:04, Mike Halmarack wrote:
> The grand kids are coming for a holiday. I have a composition
> material medicine cupboard with no lock. What is the best bit to use
> the make a clean, 20mm cylindrical hole in the door?
>
> I have a Forstner bit which I've used for some stopped housing jobs
> but to go all the way through, wouldn't I need to drill a pilot hole
> which has tended to cause loss of Forstner bit centering in the past.
> Is there a more suitable bit?
If you haven't got a drill press I think you will struggle to use a
Forstner bit in a hand-held drill (I haven't tried it) without making a
guide.

As an alternative you could use something like this:
https://www.screwfix.com/p/yale-door-security-bolts-polished-brass-76mm-2-pack/74618
Any damage around the holes is covered and you could use a simple spade bit.

On Fri, 21 Jul 2023 07:04:45 +0100, Mike Halmarack
<mikehalmarack@gmail.com> wrote:

Thanks all for the good advice. I'm going to go for the auger bit
option. The forstner bit might make a cleaner cut but for exit
purposes I'll feel more comfortable with the auger bit.
--

Mike

On Fri, 21 Jul 2023 15:08:58 +0100, nothanks@aolbin.com wrote:

>If you haven't got a drill press I think you will struggle to use a
>Forstner bit in a hand-held drill (I haven't tried it) without making a
>guide.

Naah....

But: so make a guide. Bit of wood, drill through at the angle you would like
(here: 90°). Don't do this on the workpiece, just make the hole.

Apply wood-with-hole to front of workpiece, adding a bit of undrilled wood to
the back of the workpiece. Clamp the lot.

Drill. Wood-with-hole guides & hold perpendiclular, wood in back prevents
tearing on exit.

Can't slip, can't scratch the surface, hard to get wrong...

Thomas Prufer