Cutting foam

[snowyskiesau]

I bought some camera foam (high density) to install in an aluminium case I have and
was after ideas for the best way to cut it:

Sharp knife?
Jig saw?
Hot wire cutter?

I want the job to be as neat as possible given that the foam was not cheap. Previous attempts to cut foam with a knife have not been pretty

[Striker (Tony)]

I remember someone saying put the foam in the freezer then use a sharp knife to cut it.

Dont know how well it works but worth a try

[Dennis]

I have successfully used utility knives with very sharp blades, a steel ruler and a vertical sawing action to cut out rectangular areas for e.g. camera bodies.

I have also used a drill press with 1 1/4 and 2 inch bits for eyepieces, to drill round holes, with the foam sandwiched between 2 sheets of thin ply.

It is not easy and can quite easily go wrong! Even taking great care, my efforts do not look as nice as the OEM die cut foam inserts, but they are functional and do restrain and protect the equipment as intended.

Here are some articles on CN:
http://www.cloudynights.com/item.php?item_id=419
http://www.cloudynights.com/item.php?item_id=389
http://www.cloudynights.com/item.php?item_id=398

The last one may be the one Striker refers too?


Cheers

Dennis

[bloodhound31]

Snowyskiesau,

Check out joe's foam dome page,

http://www.orednet.org/~jgarlitz/geodome.htm

His construction pages detail a hot wire cutter.

Hope this helps.

Baz

Barrys home made observatory

http://members.iinet.net.au/~armstead

[Miaplacidus (Brian)]

Originally Posted by Striker

I remember someone saying put the foam in the freezer then use a sharp knife to cut it.

Dont know how well it works but worth a try

I've heard this too, but I thought you were meant to soak the foam in water first, then freeze it, then cut it, and then dry it. Why it shouldn't then rot I've got no idea.

[DavidH]

Hi Snowy,

Cutting foam - Not sure what high density camera foam is, but have some experience cutting polystyrene foam for model aeroplane wings. Best done with a nichrome wire heated with an electric current. Normally use 24v over about 900mm of wire. Nichrome wire can be from an old jug element or you can get it at Jaycar or Smick Dith's. If, however, camera foam is more like sponge rubber, would suggest a band saw or even an electric knife. A Dremel type high speed rotary tool may also be useful if you are hollowing out small sections.

Regards,
David.

[acropolite (Phil)]

An electric carving knife also works reasonably well.

[snowyskiesau]

Thanks for all the suggestions so far. To answer a few questions:

I was told by shredder (when I bought his surplus telescopes the other day ) that a
hot knife or an electric carving knife will cut this stuff. A hot knife certainly does but it's
too difficult to control the temperature. Don't have an electric carving knife to try.

I had some nichrome wire so made up a quick and dirty hot cutter. This works well but
needs some voltage control to regulate the temperature other wise the cut is irregular.

The cutter that Clark Rubber use has a blade like a fine hacksaw. I tried a hacksaw but
it left marks, a suitable blade in a reciprocating saw might do the job. (perhaps a jig saw?)
A hole saw leaves a jagged hole no matter what speed you use, .a forstner bit in a drill
press was also a failure
I didn't think to try a Dremel so that's something else for tomorrow.
[Update: Just tried the Dremel with small grinder disk. It gives a really clean cut]

I think the hot cutter is the go but I can't see how to cut holes for eyepieces. The nichrome
wire is too thin to hold a shape. Once I get hold of a better power supply, I'll try some stainless steel
wire as suggested on one web site.

[The high density foam sold by Clark Rubber (as camera foam) is more like sponge rubber
than polystyrene foam. It's available in 25, 50 and 100mm thicknesses.
Price for the 25mm was around $8 for a 300mm x 300mm piece cut, not sure if you save
much just buying a larger sheet uncut.]

[Merlin66 (Ken)]

For eyepiece holes a wad punch is the way to go. They come in 1 1/4" and 2" ; line it up where you want the hole resting the foam on a wooden cutting board and a quick smack with the hammer does it every time.
For odd shaped holes I just use a extended sharp cutting blade with a sawing action; hold the foam as compressed as you can with a sheet of wood.

[Orion]

I wonder if a router bit spinning at a high velocity would catch on to the foam? (maybe a bit dangerous)

[snowyskiesau]

Originally Posted by Orion

I wonder if a router bit spinning at a high velocity would catch on to the foam? (maybe a bit dangerous)

Not dangerous but certainly messy

There is a bid of drag as you push the foam through the router ( I have the router mounted on a router table) and in pushing, the foam is distorted so the cut ends up off the mark. The cut was quite clean though.

[snowyskiesau]

After trying most of the methods suggested here, I'd rank my results as follows:

1. Hot wire cutting.
This gives a nice clean cut. No obvious melting shows on the cut surface (I think I was lucky with the temperature) Only useful for straight cuts as the wire is too thin to hold a shape

2. Stanley knife.
The one I used is actually an Olfa, the sort with a blade you break off to get at the next sharp bit. This has a nice rigid blade which I used fully extended. Nice clean cut. With care, it's possible to cut curves as long as the foam is not too think. (I used 25mm for the tests)

3. Dremel
The abrasive cutoff disk makes a perfect cut but as it only has a 20mm diameter, the cut is quite shallow. Using a small grinding tool, it's possible to carve the foam as well as drill holes. No tools marks were noticeable, probably because the Dremel spins at 37000 rpm.

[sheeny (Al)]

Apart from all the techniques so far described I have made my own hand cutter for 1 1/4" eyepieces...

I use a 35mm film canister, and sharpen the top edge with a file or rasp, and then cut small teeth in the sharp edge with a stanley knife.

Place it where you want to hole, and gently rotate it back and forwards. Cuts like a beauty...

Al.

[rogerg (Roger)]

Originally Posted by acropolite

An electric carving knife also works reasonably well.

That's what I've always used. Works really well as you can make sharp corners etc quite easy and neatly because it's doing the sawing action for you so you just hold it steady and carve precisely as you want.

[74tuc]

Cutting polystyrene foam accurately is an art. I use to construct wing cores (upto 2.8M across), for all types of RC models, out of foam. My suggestion is to look at aero-modeller and model aircraft construction for the best tips. Do a search for "patern aircraft" and see what you can find,

Jerry,

[74tuc]

sorry about the typo

Patern should read Pattern

Jerry