We all know the problem about cutting foam insulation board with a saw -
the kerf is converted into showers of "snow".

The best tool I've found for this job is a bread-knife with a scalloped
edge. Having no teeth, it doesn't make a kerf, while the scalloping
helps with the sawing action. Second best is a fully extended snap-off
knife (trying to avoid the 'snap' feature). But in both cases the
narrow blade makes it difficult to follow a long straight line.

Is there such a thing as a broader blade that has no teeth but a plain
sharp edge, preferably scalloped like the bread-knife - either looking
like a small hand saw, or maybe a blade for the circular saw?



--
Ian White

In article ,
Ian White writes:

We all know the problem about cutting foam insulation board with a saw -
the kerf is converted into showers of "snow".

The best tool I've found for this job is a bread-knife with a scalloped
edge. Having no teeth, it doesn't make a kerf, while the scalloping
helps with the sawing action. Second best is a fully extended snap-off
knife (trying to avoid the 'snap' feature). But in both cases the
narrow blade makes it difficult to follow a long straight line.

Is there such a thing as a broader blade that has no teeth but a plain
sharp edge, preferably scalloped like the bread-knife - either looking
like a small hand saw, or maybe a blade for the circular saw?

I used an old break knife. I think you'll find a broader
knife gets difficult because of the extra friction.

Wash it very well after use. Many of these foam insulation
boards are expanded using nasty cyanide compounds (you can
smell them as you cut through). I don't know what risk that
brings, but I didn't risk it and haven't used the knife on
foodstuffs since.

--
Andrew Gabriel

Ian White wrote:

The best tool I've found for this job is a bread-knife with a scalloped
edge. Having no teeth, it doesn't make a kerf, while the scalloping
helps with the sawing action. Second best is a fully extended snap-off
knife (trying to avoid the 'snap' feature). But in both cases the
narrow blade makes it difficult to follow a long straight line.

I just use the "score'n snap" technique with a normal Stanley knife,
running the blade along a straight edge. Works fine for me.

David

Ian White wrote:

We all know the problem about cutting foam insulation board with a saw -
the kerf is converted into showers of "snow".

The best tool I've found for this job is a bread-knife with a scalloped
edge. Having no teeth, it doesn't make a kerf, while the scalloping
helps with the sawing action. Second best is a fully extended snap-off
knife (trying to avoid the 'snap' feature). But in both cases the
narrow blade makes it difficult to follow a long straight line.

Is there such a thing as a broader blade that has no teeth but a plain
sharp edge, preferably scalloped like the bread-knife - either looking
like a small hand saw, or maybe a blade for the circular saw?




I noticed a double glazing installer using a broken hacksaw blade to cut
back the foam round the edges of the window. Nice clean cut, and no
sweeping up. I think you need a kerf, but a small one.
There used to be a broad hacksaw blade on a handle, rather like a
padsaw, but I haven't seen them recently

Stuart Noble wrote:

Is there such a thing as a broader blade that has no teeth but a
plain sharp edge, preferably scalloped like the bread-knife - either
looking like a small hand saw, or maybe a blade for the circular saw?

The shops that cut foam into cushion size pieces use a jigsaw with a long
smooth blade. Don't know where they get them though.

I have also seen it done with an electric carving knife.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

On Sat, 15 Jul 2006 14:16:18 +0100, Ian White
wrote:


We all know the problem about cutting foam insulation board with a saw -
the kerf is converted into showers of "snow".

The best tool I've found for this job is a bread-knife with a scalloped
edge. Having no teeth, it doesn't make a kerf, while the scalloping
helps with the sawing action. Second best is a fully extended snap-off
knife (trying to avoid the 'snap' feature). But in both cases the
narrow blade makes it difficult to follow a long straight line.

Is there such a thing as a broader blade that has no teeth but a plain
sharp edge, preferably scalloped like the bread-knife - either looking
like a small hand saw, or maybe a blade for the circular saw?


Last time I needed to do loads of polystyrene, I rigged up a long hot
wire with a biggish battery charger and 0.8mm MIG wire with a sheet of
chipboard as a back-plate, bowed to act as a spring.

Well worth the effort if you have a lot to do. Dead straight cuts
along the whole length of a sheet in about 2 seconds and no mess
at-all.

Cheers,

Colin.

The message
from Ian White contains these words:

The best tool I've found for this job is a bread-knife with a scalloped
edge.

I made a hot-wire cutter. Much easier.

--
Skipweasel
Pay no attention to that man behind the curtain.

On Sat, 15 Jul 2006 19:38:31 +0100, Guy King
had this to say:

The message
from Ian White contains these words:

The best tool I've found for this job is a bread-knife with a scalloped
edge.

I made a hot-wire cutter. Much easier.

So did I, many years ago. I made a frame a bit like a fretsaw out of a
bit of plywood and a handle of a table-tennis bat (!), fitted two
screw terminals and a bit of flex wired to a 4V ex-wireless-set
transformer.
Worked a treat, as long as you didn't stop the "cut" for more than a
second or two - if you did, you'd develop a hole.

--
Frank Erskine

On Sat, 15 Jul 2006 19:56:33 +0100, Frank Erskine
had this to say:

On Sat, 15 Jul 2006 19:38:31 +0100, Guy King
had this to say:

The message
from Ian White contains these words:

The best tool I've found for this job is a bread-knife with a scalloped
edge.

I made a hot-wire cutter. Much easier.

So did I, many years ago. I made a frame a bit like a fretsaw out of a
bit of plywood and a handle of a table-tennis bat (!), fitted two
screw terminals and a bit of flex wired to a 4V ex-wireless-set
transformer.

Oh - and a bit of element wire from a nelectric fire!

Worked a treat, as long as you didn't stop the "cut" for more than a
second or two - if you did, you'd develop a hole.

--
Frank Erskine

Guy King wrote:

The message
from Ian White contains these words:


The best tool I've found for this job is a bread-knife with a scalloped
edge.


I made a hot-wire cutter. Much easier.

I can see that would work for jablite (i.e. polystyrene), but would it
work for foil covered PIR foam like celotex or kingspan etc?

--
Cheers,

John.

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

The message
from John Rumm contains these words:

I made a hot-wire cutter. Much easier.

I can see that would work for jablite (i.e. polystyrene), but would it
work for foil covered PIR foam like celotex or kingspan etc?

No. You'd have to slit the foil first.

--
Skipweasel
Pay no attention to that man behind the curtain.

Stuart Noble wrote:
Ian White wrote:

We all know the problem about cutting foam insulation board with a saw
- the kerf is converted into showers of "snow".

The best tool I've found for this job is a bread-knife with a
scalloped edge. Having no teeth, it doesn't make a kerf, while the
scalloping helps with the sawing action. Second best is a fully
extended snap-off knife (trying to avoid the 'snap' feature). But in
both cases the narrow blade makes it difficult to follow a long
straight line.

Is there such a thing as a broader blade that has no teeth but a plain
sharp edge, preferably scalloped like the bread-knife - either looking
like a small hand saw, or maybe a blade for the circular saw?




I noticed a double glazing installer using a broken hacksaw blade to cut
back the foam round the edges of the window. Nice clean cut, and no
sweeping up. I think you need a kerf, but a small one.
There used to be a broad hacksaw blade on a handle, rather like a
padsaw, but I haven't seen them recently

I used a small 'kitchen devil' serrated steak knife for that..

Thanks for all the suggestions.

Normally I would score and snap the boards too, but further into the job
it will be necessary to piece together some of the large offcuts, so it
would be nice to have straight, flat, full-depth cut edges.

Based on all the other suggestions have led to a cunning plan:

1. Use score-and-snap, the breadknife and possibly the tenon saw, but
only to line the workshop walls where the benches are going to be.

2. Build some workbenches (at last!)

3. Find wherever I packed the big low-voltage transformer and variac
before the house move... and then have some fun with a hot wire cutter.


Thanks again!
--
Ian White

Ian White wrote:

Thanks for all the suggestions.

Normally I would score and snap the boards too, but further into the job
it will be necessary to piece together some of the large offcuts, so it
would be nice to have straight, flat, full-depth cut edges.

Based on all the other suggestions have led to a cunning plan:

1. Use score-and-snap, the breadknife and possibly the tenon saw, but
only to line the workshop walls where the benches are going to be.

2. Build some workbenches (at last!)

3. Find wherever I packed the big low-voltage transformer and variac
before the house move... and then have some fun with a hot wire cutter.


Thanks again!
Don't hot wire cut Celotex stuff. NASTY fumes.

Ian White wrote:

Thanks for all the suggestions.


3. Find wherever I packed the big low-voltage transformer and variac
before the house move... and then have some fun with a hot wire cutter.




I needed to cut and shape some polystyrene and made a very simple hot
wire cutter from a steel guitar string ( the thinnest one you can easily
get ). The transformer was one from a low-voltage lighting system ( it
was about 120W @ 12 V, but didn't need to be that powerful ). Fne
control was with a variac controlling the voltage into the transformer
primary, just like you mentioned that you already have. The wire was
held under tension in a gadget that looked like an oversized fret saw.
The metal parts from electrical choc-block connecters made good
connections to the guitar string and also acted as a mechanical anchor
point to keep it under tension.

The fine control made all the difference to how efficiently I could make
it cut, but for anybody without a variac, they might find that using
bulldog clips and sections of a wire-wrapped 1KW bar element in series
with the cutting wire, it's possible to regulate the current as desired.

Safety police saying the bleeding obvious ...
Beware that the wire and regulator may get pretty hot.

The Medway Handyman wrote:

The shops that cut foam into cushion size pieces use a jigsaw with a long
smooth blade. Don't know where they get them though.

I modded a jigsaw blade with an angle grinder to remove the teeth (metal
cutting blade)providing just a sharp edge.
It was just long enough to all but pierce the opposite layer of foil, so
a follow-up with a stanley knife sorted that out.


--
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