Has anyone any bright ideas how to make shallow, blind holes in closed
cell foam? It is Plastazote foam so quite dense and stiff.

I want to make 12mm or 15mm diameter depressions about 3mm deep (the
foam is 10mm thick).

I was wondering if using a plunge router or a pillar drill with a
forstner bit might work. I have a router and a small, quite high
speed, pillar drill. I don't at present have any forstner bits.

So I will probably try the router but opinions on the forstner bit
instead would be welcome.

--
Chris Green
·

On 08/04/2024 16:33, Chris Green wrote:
> Has anyone any bright ideas how to make shallow, blind holes in closed
> cell foam? It is Plastazote foam so quite dense and stiff.
>
> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> foam is 10mm thick).
>
> I was wondering if using a plunge router or a pillar drill with a
> forstner bit might work. I have a router and a small, quite high
> speed, pillar drill. I don't at present have any forstner bits.
>
> So I will probably try the router but opinions on the forstner bit
> instead would be welcome.
>
Something hot?

On 08/04/2024 16:33, Chris Green wrote:
> Has anyone any bright ideas how to make shallow, blind holes in closed
> cell foam? It is Plastazote foam so quite dense and stiff.
>
> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> foam is 10mm thick).
>
> I was wondering if using a plunge router or a pillar drill with a
> forstner bit might work. I have a router and a small, quite high
> speed, pillar drill. I don't at present have any forstner bits.
>
> So I will probably try the router but opinions on the forstner bit
> instead would be welcome.
>

A router will give you a flat bottomed hole, and accurate control of the
depth. You could probably stick a router bit in the pillar drill if you
wanted...

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

John Rumm <see.my.signature@nowhere.null> wrote:
> On 08/04/2024 16:33, Chris Green wrote:
> > Has anyone any bright ideas how to make shallow, blind holes in closed
> > cell foam? It is Plastazote foam so quite dense and stiff.
> >
> > I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> > foam is 10mm thick).
> >
> > I was wondering if using a plunge router or a pillar drill with a
> > forstner bit might work. I have a router and a small, quite high
> > speed, pillar drill. I don't at present have any forstner bits.
> >
> > So I will probably try the router but opinions on the forstner bit
> > instead would be welcome.
> >
>
> A router will give you a flat bottomed hole, and accurate control of the
> depth. You could probably stick a router bit in the pillar drill if you
> wanted...
>
"A router bit in the pillar drill", that's an idea which will be easy
to try, thank you. I may actually get round to trying it later today.
I will report on results.

--
Chris Green
·

Chris Green wrote:

> Has anyone any bright ideas how to make shallow, blind holes in closed
> cell foam?

red-hot poker?

Chris Green <cl@isbd.net> wrote:
> John Rumm <see.my.signature@nowhere.null> wrote:
> > On 08/04/2024 16:33, Chris Green wrote:
> > > Has anyone any bright ideas how to make shallow, blind holes in closed
> > > cell foam? It is Plastazote foam so quite dense and stiff.
> > >
> > > I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> > > foam is 10mm thick).
> > >
> > > I was wondering if using a plunge router or a pillar drill with a
> > > forstner bit might work. I have a router and a small, quite high
> > > speed, pillar drill. I don't at present have any forstner bits.
> > >
> > > So I will probably try the router but opinions on the forstner bit
> > > instead would be welcome.
> > >
> >
> > A router will give you a flat bottomed hole, and accurate control of the
> > depth. You could probably stick a router bit in the pillar drill if you
> > wanted...
> >
> "A router bit in the pillar drill", that's an idea which will be easy
> to try, thank you. I may actually get round to trying it later today.
> I will report on results.
>
It worked pretty well in that it cut away the foam neatly but it
didn't produce a flat bottomed hole, it cut a neat circular channel. I
think maybe some Forstner bits may get closer to the flat bottom I'm
after.

--
Chris Green
·

On 09/04/2024 17:51, Chris Green wrote:
> Chris Green <cl@isbd.net> wrote:
>> John Rumm <see.my.signature@nowhere.null> wrote:
>>> On 08/04/2024 16:33, Chris Green wrote:
>>>> Has anyone any bright ideas how to make shallow, blind holes in closed
>>>> cell foam? It is Plastazote foam so quite dense and stiff.
>>>>
>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
>>>> foam is 10mm thick).
>>>>
>>>> I was wondering if using a plunge router or a pillar drill with a
>>>> forstner bit might work. I have a router and a small, quite high
>>>> speed, pillar drill. I don't at present have any forstner bits.
>>>>
>>>> So I will probably try the router but opinions on the forstner bit
>>>> instead would be welcome.
>>>>
>>>
>>> A router will give you a flat bottomed hole, and accurate control of the
>>> depth. You could probably stick a router bit in the pillar drill if you
>>> wanted...
>>>
>> "A router bit in the pillar drill", that's an idea which will be easy
>> to try, thank you. I may actually get round to trying it later today.
>> I will report on results.
>>
> It worked pretty well in that it cut away the foam neatly but it
> didn't produce a flat bottomed hole, it cut a neat circular channel. I
> think maybe some Forstner bits may get closer to the flat bottom I'm
> after.
>

A Forstner bit would certainly be my first choice. Even they have a
small locating spike in the middle, so the bottom won't be totally flat
unless you grind off the spike.

Aldi and Lidl often have cheap sets which would probably be sufficient
for your purposes.
--
Cheers,
Roger

On 08/04/2024 16:33, Chris Green wrote:
> Has anyone any bright ideas how to make shallow, blind holes in closed
> cell foam? It is Plastazote foam so quite dense and stiff.
>
> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> foam is 10mm thick).
>
> I was wondering if using a plunge router or a pillar drill with a
> forstner bit might work. I have a router and a small, quite high
> speed, pillar drill. I don't at present have any forstner bits.
>
> So I will probably try the router but opinions on the forstner bit
> instead would be welcome.
>
If a heated rod can't be used then:
- make a D bit. Take a rod (drill, silver steel, bolt) of correct
diameter, grind off a section so that the profile is a D shape (flat
section just less than the diameter), file a bit of relief on the
leading edge (might not need that for foam).
or
- buy a slot drill of the right size (google)

Roger Mills <mills37.fslife@gmail.com> wrote:
> On 09/04/2024 17:51, Chris Green wrote:
> > Chris Green <cl@isbd.net> wrote:
> >> John Rumm <see.my.signature@nowhere.null> wrote:
> >>> On 08/04/2024 16:33, Chris Green wrote:
> >>>> Has anyone any bright ideas how to make shallow, blind holes in closed
> >>>> cell foam? It is Plastazote foam so quite dense and stiff.
> >>>>
> >>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> >>>> foam is 10mm thick).
> >>>>
> >>>> I was wondering if using a plunge router or a pillar drill with a
> >>>> forstner bit might work. I have a router and a small, quite high
> >>>> speed, pillar drill. I don't at present have any forstner bits.
> >>>>
> >>>> So I will probably try the router but opinions on the forstner bit
> >>>> instead would be welcome.
> >>>>
> >>>
> >>> A router will give you a flat bottomed hole, and accurate control of the
> >>> depth. You could probably stick a router bit in the pillar drill if you
> >>> wanted...
> >>>
> >> "A router bit in the pillar drill", that's an idea which will be easy
> >> to try, thank you. I may actually get round to trying it later today.
> >> I will report on results.
> >>
> > It worked pretty well in that it cut away the foam neatly but it
> > didn't produce a flat bottomed hole, it cut a neat circular channel. I
> > think maybe some Forstner bits may get closer to the flat bottom I'm
> > after.
> >
>
> A Forstner bit would certainly be my first choice. Even they have a
> small locating spike in the middle, so the bottom won't be totally flat
> unless you grind off the spike.
>
> Aldi and Lidl often have cheap sets which would probably be sufficient
> for your purposes.

The hole in the middle won't matter. I've ordered a cheap set from
Amazon for the princely sum of £14.99. it has the 10mm, 12mm and 15mm
diameters I need (plus 16 others!).

They should arrive today so we'll see! :-)

--
Chris Green
·

On 10/04/2024 09:35, Chris Green wrote:
> Roger Mills <mills37.fslife@gmail.com> wrote:
>> On 09/04/2024 17:51, Chris Green wrote:
>>> Chris Green <cl@isbd.net> wrote:
>>>> John Rumm <see.my.signature@nowhere.null> wrote:
>>>>> On 08/04/2024 16:33, Chris Green wrote:
>>>>>> Has anyone any bright ideas how to make shallow, blind holes in closed
>>>>>> cell foam? It is Plastazote foam so quite dense and stiff.
>>>>>>
>>>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
>>>>>> foam is 10mm thick).
>>>>>>
>>>>>> I was wondering if using a plunge router or a pillar drill with a
>>>>>> forstner bit might work. I have a router and a small, quite high
>>>>>> speed, pillar drill. I don't at present have any forstner bits.
>>>>>>
>>>>>> So I will probably try the router but opinions on the forstner bit
>>>>>> instead would be welcome.
>>>>>>
>>>>>
>>>>> A router will give you a flat bottomed hole, and accurate control of the
>>>>> depth. You could probably stick a router bit in the pillar drill if you
>>>>> wanted...
>>>>>
>>>> "A router bit in the pillar drill", that's an idea which will be easy
>>>> to try, thank you. I may actually get round to trying it later today.
>>>> I will report on results.
>>>>
>>> It worked pretty well in that it cut away the foam neatly but it
>>> didn't produce a flat bottomed hole, it cut a neat circular channel. I
>>> think maybe some Forstner bits may get closer to the flat bottom I'm
>>> after.
>>>
>>
>> A Forstner bit would certainly be my first choice. Even they have a
>> small locating spike in the middle, so the bottom won't be totally flat
>> unless you grind off the spike.
>>
>> Aldi and Lidl often have cheap sets which would probably be sufficient
>> for your purposes.
>
> The hole in the middle won't matter. I've ordered a cheap set from
> Amazon for the princely sum of £14.99. it has the 10mm, 12mm and 15mm
> diameters I need (plus 16 others!).
>
> They should arrive today so we'll see! :-)

Although nothing in the size you want, the hole cutters made of plastic
used for cutting shallow holes in (exterior) foam insulation are
somewhat open probably to allow balled up foam to easily escape during
drilling.

https://www.shopewi.co.uk/product/plastic-ewi-router-for-eps-insulation-boards/

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

On 10/04/2024 10:23, alan_m wrote:
> On 10/04/2024 09:35, Chris Green wrote:
>> Roger Mills <mills37.fslife@gmail.com> wrote:
>>> On 09/04/2024 17:51, Chris Green wrote:
>>>> Chris Green <cl@isbd.net> wrote:
>>>>> John Rumm <see.my.signature@nowhere.null> wrote:
>>>>>> On 08/04/2024 16:33, Chris Green wrote:
>>>>>>> Has anyone any bright ideas how to make shallow, blind holes in
>>>>>>> closed
>>>>>>> cell foam?  It is Plastazote foam so quite dense and stiff.
>>>>>>>
>>>>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
>>>>>>> foam is 10mm thick).
>>>>>>>
>>>>>>> I was wondering if using a plunge router or a pillar drill with a
>>>>>>> forstner bit might work.  I have a router and a small, quite high
>>>>>>> speed, pillar drill.  I don't at present have any forstner bits.
>>>>>>>
>>>>>>> So I will probably try the router but opinions on the forstner bit
>>>>>>> instead would be welcome.
>>>>>>>
>>>>>>
>>>>>> A router will give you a flat bottomed hole, and accurate control
>>>>>> of the
>>>>>> depth. You could probably stick a router bit in the pillar drill
>>>>>> if you
>>>>>> wanted...
>>>>>>
>>>>> "A router bit in the pillar drill", that's an idea which will be easy
>>>>> to try, thank you.  I may actually get round to trying it later today.
>>>>> I will report on results.
>>>>>
>>>> It worked pretty well in that it cut away the foam neatly but it
>>>> didn't produce a flat bottomed hole, it cut a neat circular channel. I
>>>> think maybe some Forstner bits may get closer to the flat bottom I'm
>>>> after.
>>>>
>>>
>>> A Forstner bit would certainly be my first choice. Even they have a
>>> small locating spike in the middle, so the bottom won't be totally flat
>>> unless you grind off the spike.
>>>
>>> Aldi and Lidl often have cheap sets which would probably be sufficient
>>> for your purposes.
>>
>> The hole in the middle won't matter.  I've ordered a cheap set from
>> Amazon for the princely sum of £14.99. it has the 10mm, 12mm and 15mm
>> diameters I need (plus 16 others!).
>>
>> They should arrive today so we'll see! :-)
>
> Although nothing in the size you want, the hole cutters made of plastic
> used for cutting shallow holes in (exterior) foam insulation are
> somewhat open probably to allow balled up foam to easily escape during
> drilling.
>
> https://www.shopewi.co.uk/product/plastic-ewi-router-for-eps-insulation-boards/
>
>
>
That is simply a hole saw. and if the pilot hole it leaves is not an
issue why not get a proper set..?

https://www.diy.com/departments/carbon-steel-5-piece-holesaw-set/1732845_BQ.prd

Hardly a bank breaker

But I see you already spent more at amazon :-)

--
“It is dangerous to be right in matters on which the established
authorities are wrong.”

― Voltaire, The Age of Louis XIV

On 10/04/2024 10:45, The Natural Philosopher wrote:
> On 10/04/2024 10:23, alan_m wrote:
>> On 10/04/2024 09:35, Chris Green wrote:
>>> Roger Mills <mills37.fslife@gmail.com> wrote:
>>>> On 09/04/2024 17:51, Chris Green wrote:
>>>>> Chris Green <cl@isbd.net> wrote:
>>>>>> John Rumm <see.my.signature@nowhere.null> wrote:
>>>>>>> On 08/04/2024 16:33, Chris Green wrote:
>>>>>>>> Has anyone any bright ideas how to make shallow, blind holes in
>>>>>>>> closed
>>>>>>>> cell foam?  It is Plastazote foam so quite dense and stiff.
>>>>>>>>
>>>>>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep
>>>>>>>> (the
>>>>>>>> foam is 10mm thick).
>>>>>>>>
>>>>>>>> I was wondering if using a plunge router or a pillar drill with a
>>>>>>>> forstner bit might work.  I have a router and a small, quite high
>>>>>>>> speed, pillar drill.  I don't at present have any forstner bits.
>>>>>>>>
>>>>>>>> So I will probably try the router but opinions on the forstner bit
>>>>>>>> instead would be welcome.
>>>>>>>>
>>>>>>>
>>>>>>> A router will give you a flat bottomed hole, and accurate control
>>>>>>> of the
>>>>>>> depth. You could probably stick a router bit in the pillar drill
>>>>>>> if you
>>>>>>> wanted...
>>>>>>>
>>>>>> "A router bit in the pillar drill", that's an idea which will be easy
>>>>>> to try, thank you.  I may actually get round to trying it later
>>>>>> today.
>>>>>> I will report on results.
>>>>>>
>>>>> It worked pretty well in that it cut away the foam neatly but it
>>>>> didn't produce a flat bottomed hole, it cut a neat circular channel. I
>>>>> think maybe some Forstner bits may get closer to the flat bottom I'm
>>>>> after.
>>>>>
>>>>
>>>> A Forstner bit would certainly be my first choice. Even they have a
>>>> small locating spike in the middle, so the bottom won't be totally flat
>>>> unless you grind off the spike.
>>>>
>>>> Aldi and Lidl often have cheap sets which would probably be sufficient
>>>> for your purposes.
>>>
>>> The hole in the middle won't matter.  I've ordered a cheap set from
>>> Amazon for the princely sum of £14.99. it has the 10mm, 12mm and 15mm
>>> diameters I need (plus 16 others!).
>>>
>>> They should arrive today so we'll see! :-)
>>
>> Although nothing in the size you want, the hole cutters made of
>> plastic used for cutting shallow holes in (exterior) foam insulation
>> are somewhat open probably to allow balled up foam to easily escape
>> during drilling.
>>
>> https://www.shopewi.co.uk/product/plastic-ewi-router-for-eps-insulation-boards/
>>
>>
>>
> That is simply a hole saw.  and if the pilot hole it leaves  is not an
> issue why not get a proper set..?

It is not a normal hole saw since it has radial teeth as well - it is
designed to mill out a cylindrical pocket, not just cut the annulus.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 10/04/2024 11:11, John Rumm wrote:

> It is not a normal hole saw since it has radial teeth as well - it is
> designed to mill out a cylindrical pocket, not just cut the annulus.

Usage
https://youtu.be/96WN8AtAvNg?t=752

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

The Natural Philosopher <tnp@invalid.invalid> wrote:
> >>> A Forstner bit would certainly be my first choice. Even they have a
> >>> small locating spike in the middle, so the bottom won't be totally flat
> >>> unless you grind off the spike.
> >>>
> >>> Aldi and Lidl often have cheap sets which would probably be sufficient
> >>> for your purposes.
> >>
> >> The hole in the middle won't matter.  I've ordered a cheap set from
> >> Amazon for the princely sum of £14.99. it has the 10mm, 12mm and 15mm
> >> diameters I need (plus 16 others!).
> >>
> >> They should arrive today so we'll see! :-)
> >
> > Although nothing in the size you want, the hole cutters made of plastic
> > used for cutting shallow holes in (exterior) foam insulation are
> > somewhat open probably to allow balled up foam to easily escape during
> > drilling.
> >
> > https://www.shopewi.co.uk/product/plastic-ewi-router-for-eps-insulation-boards/
> >
> >
> >
> That is simply a hole saw. and if the pilot hole it leaves is not an
> issue why not get a proper set..?
>
> https://www.diy.com/departments/carbon-steel-5-piece-holesaw-set/1732845_BQ.prd
>
> Hardly a bank breaker
>
> But I see you already spent more at amazon :-)
>
A hole saw doesn't work for blind holes. It would simply cut a slot
round the piece of foam I want to extract but it wouldn't remove the
middle.

I have lots of hole saws, very useful for cutting holes right through
things but not for blind holes.

--
Chris Green
·

On 09/04/2024 17:51, Chris Green wrote:
> Chris Green <cl@isbd.net> wrote:
>> John Rumm <see.my.signature@nowhere.null> wrote:
>>> On 08/04/2024 16:33, Chris Green wrote:
>>>> Has anyone any bright ideas how to make shallow, blind holes in closed
>>>> cell foam? It is Plastazote foam so quite dense and stiff.
>>>>
>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
>>>> foam is 10mm thick).
>>>>
>>>> I was wondering if using a plunge router or a pillar drill with a
>>>> forstner bit might work. I have a router and a small, quite high
>>>> speed, pillar drill. I don't at present have any forstner bits.
>>>>
>>>> So I will probably try the router but opinions on the forstner bit
>>>> instead would be welcome.
>>>>
>>>
>>> A router will give you a flat bottomed hole, and accurate control of the
>>> depth. You could probably stick a router bit in the pillar drill if you
>>> wanted...
>>>
>> "A router bit in the pillar drill", that's an idea which will be easy
>> to try, thank you. I may actually get round to trying it later today.
>> I will report on results.
>>
> It worked pretty well in that it cut away the foam neatly but it
> didn't produce a flat bottomed hole, it cut a neat circular channel.

What kind of router cutter was it (straight flute, or up cut / down cut
spiral)?

Also small router cutters normally expect fairly high RPMs - 20K ish -
so the cut may not be as clean at drill speeds.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

John Rumm <see.my.signature@nowhere.null> wrote:
> On 09/04/2024 17:51, Chris Green wrote:
> > Chris Green <cl@isbd.net> wrote:
> >> John Rumm <see.my.signature@nowhere.null> wrote:
> >>> On 08/04/2024 16:33, Chris Green wrote:
> >>>> Has anyone any bright ideas how to make shallow, blind holes in closed
> >>>> cell foam? It is Plastazote foam so quite dense and stiff.
> >>>>
> >>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> >>>> foam is 10mm thick).
> >>>>
> >>>> I was wondering if using a plunge router or a pillar drill with a
> >>>> forstner bit might work. I have a router and a small, quite high
> >>>> speed, pillar drill. I don't at present have any forstner bits.
> >>>>
> >>>> So I will probably try the router but opinions on the forstner bit
> >>>> instead would be welcome.
> >>>>
> >>>
> >>> A router will give you a flat bottomed hole, and accurate control of the
> >>> depth. You could probably stick a router bit in the pillar drill if you
> >>> wanted...
> >>>
> >> "A router bit in the pillar drill", that's an idea which will be easy
> >> to try, thank you. I may actually get round to trying it later today.
> >> I will report on results.
> >>
> > It worked pretty well in that it cut away the foam neatly but it
> > didn't produce a flat bottomed hole, it cut a neat circular channel.
>
> What kind of router cutter was it (straight flute, or up cut / down cut
> spiral)?
>
It was a 'straight' cutter for making parallel sided round holes. It's
from a set I bought many years ago (20+) from Screwfix I think. It
cut quite well (i.e. cleanly) the issue is that the cutters on the
sides project a couple of mm beyond the cutter on the end that removes
material from the hole. Thus for my 2mm or 3mm deep holes it didn't
work too well.

> Also small router cutters normally expect fairly high RPMs - 20K ish -
> so the cut may not be as clean at drill speeds.
>
--
Chris Green
·

On 10/04/2024 17:19, Chris Green wrote:
> John Rumm <see.my.signature@nowhere.null> wrote:
>> On 09/04/2024 17:51, Chris Green wrote:
>>> Chris Green <cl@isbd.net> wrote:
>>>> John Rumm <see.my.signature@nowhere.null> wrote:
>>>>> On 08/04/2024 16:33, Chris Green wrote:
>>>>>> Has anyone any bright ideas how to make shallow, blind holes in closed
>>>>>> cell foam? It is Plastazote foam so quite dense and stiff.
>>>>>>
>>>>>> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
>>>>>> foam is 10mm thick).
>>>>>>
>>>>>> I was wondering if using a plunge router or a pillar drill with a
>>>>>> forstner bit might work. I have a router and a small, quite high
>>>>>> speed, pillar drill. I don't at present have any forstner bits.
>>>>>>
>>>>>> So I will probably try the router but opinions on the forstner bit
>>>>>> instead would be welcome.
>>>>>>
>>>>>
>>>>> A router will give you a flat bottomed hole, and accurate control of the
>>>>> depth. You could probably stick a router bit in the pillar drill if you
>>>>> wanted...
>>>>>
>>>> "A router bit in the pillar drill", that's an idea which will be easy
>>>> to try, thank you. I may actually get round to trying it later today.
>>>> I will report on results.
>>>>
>>> It worked pretty well in that it cut away the foam neatly but it
>>> didn't produce a flat bottomed hole, it cut a neat circular channel.
>>
>> What kind of router cutter was it (straight flute, or up cut / down cut
>> spiral)?
>>
> It was a 'straight' cutter for making parallel sided round holes. It's
> from a set I bought many years ago (20+) from Screwfix I think. It
> cut quite well (i.e. cleanly) the issue is that the cutters on the
> sides project a couple of mm beyond the cutter on the end that removes
> material from the hole. Thus for my 2mm or 3mm deep holes it didn't
> work too well.
Grind the protruding bits off the bottom of the cutters ...
>
>> Also small router cutters normally expect fairly high RPMs - 20K ish -
>> so the cut may not be as clean at drill speeds.
>>

The Natural Philosopher wrote:

> alan_m wrote:
>
>> https://www.shopewi.co.uk/product/plastic-ewi-router-for-eps-insulation-boards/
>
> That is simply a hole saw.

No, it does have "end" cutters on the cruciform section ...

Chris Green <cl@isbd.net> wrote:
> Has anyone any bright ideas how to make shallow, blind holes in closed
> cell foam? It is Plastazote foam so quite dense and stiff.
>
> I want to make 12mm or 15mm diameter depressions about 3mm deep (the
> foam is 10mm thick).
>
> I was wondering if using a plunge router or a pillar drill with a
> forstner bit might work. I have a router and a small, quite high
> speed, pillar drill. I don't at present have any forstner bits.
>
> So I will probably try the router but opinions on the forstner bit
> instead would be welcome.
>
.... and the forstner bits work well in my little pillar drill making a
neat, flat bottomed hole with a little depression in the middle that
doesn't matter at all as it's going to have a thin screw through there
anyway.

--
Chris Green
·