Cutting polystyrene board

[tefer2]

How is everyone cutting rigid polystyrene board ? I thought maybe the table saw ?

[BlueBee]

I have used a table saw and I’ve use a hot wire cutter, the table saw is definitely easier!

I would urge safety first when cutting foam.  I always wear a good respirator, goggles, earplugs, and gloves.  Yes, I‘m a bit of a safety freak, but it’s easier to replace foam than body parts.  Also beware that thick foam has a tendency to bind the blade on occasion.

[tefer2]

Yea, I had the feeling that tiny particles would be everywhere with the table saw. Thanks

[Robo]

+1 for tablesaw.  Makes a real nice clean cut.

[bulldog]

definitely use the table saw. i used to work in a plastics factory, cut all kinds of plastics with a table saw. just take your
time and cut slow ( don't push it through to fast ) or as i always say let the blade do the cutting. otherwise it could chatter and crack on you. and i'd also agree on wearing a mask. you don't want to breath that nasty stuff.

[Michael Bush]

A sharp knife and a quick break.

[BlueBee]

Yep, a sharp knife works.  I can remember cutting some with a knife in the Home Depot parking lot when it was 19F outside and blowing the wind!  Brrrrrr.  I didn’t have the trailer and needed to cut it down to size to fit in the car. 

Normally they will cut foam for you at HD if you ask.  Normally they use a dull knife and a quick break.  I believe it is against store policy to cut the stuff on their panel saw because of the particulates it puts into the air. 

How about a bonus question for this thread? 

How do people glue polystyrene together?  What sticks?  What doesn't?

[Keskin]

Polyurethane marine glues are my favourite.

[Michael Bush]

>How do people glue polystyrene together?  What sticks?  What doesn't?

Styrene glue (model car etc.) would seem like it would but it just melts it into oblivion.  Oil based paints have the same effect so if you're paining use latex based.  I've had good luck with Elmer's exterior carpenter glue and then paint with latex to keep the water out.

[S.M.N.Bee]

I use PL 300 foam board adhesive. Made by Loctite. Sold at Menyards. Works good.

John

[JRH]

Having tried the table saw - problems and dangerous catching in the blade - AND having tried hot wire cutting - the FUMES are deadly - I recommend a good sharp knife.  If you want a nice cut that's square from top to bottom and side to side, I suggest cutting two pieces of plywood to the length and width of the finished piece you want as a template.  Sandwich the foam in between, clamp, and cut.

[windfall]

I agree the 2" foam is a bit sketchy on the table saw. You have to really pay attention to your feed direction and pressure since the foam does expand slightly when compressed, unlike wood. Lot's of folks tend to keep a good bit of pressure when cutting wood against the fence...and it works well. You can't do this with foam. Just enough to keep it tight and the rest of your push in line with the blade.

[BlueBee]

JRH is right about the fumes if you try to cut the stuff with a hot wire! 

I have done it outside, but the fumes are still an issue and the kerf of the cut varies when using a hot wire.  If you slow down, or stop, you get a wider cut as the heat has more time to work against the foam.  You get a faster, cleaner cut with the table saw.

I find cutting the 2” stuff to be the most liable to bind the saw until you get a feel for it, as Windfall says.  The thinner stuff, like ¾”, cuts very nicely on a table saw.

[derekm]

For cutting polystryene foam I used a jig saw with a scalopped knife blade designed for the job.
for cutting polyurethane foam  band saw, table saw, router all work well. polyurethane is much easier to work tha polystyrene. In fact its used to teach CNC

[bulldog]

ok i'm confused. are we talking about polystyrene ( a rigid plastic ) or polystyrene foam ( aka styrofoam ) ?  if the latter than i'd go with a straight edge and a razor knife.

[PeeVee]

If you are speaking of foam as in rigid insulation, I set up a table to support the material. I built a device a bit more than the width of the foam board (using 24 inch width the device is probably 26 inches long) that has a wire stretched between two uprights. The wire being tight. Using my automotive battery charger, the wire gets hot. Do not touch the wire! Mark the foam where a cut is to be made. I prefer the supports to be high enough that the foam rests under the wire. Draw the foam up and a clean cut is made.

[BlueBee]

PeeVee, are you using a commercial hot wire cutter, or something you rigged up yourself?  Are you using any special kind of wire, like NiCr?  What is the gauge of the wire? 

I’m just curious.  I built a homemade wire cutter last spring and powered it with a computer power supply.  It cut foam OK, but mine didn’t cut as clean or as fast as a table saw.  Always interested in better ways to do things.

[PeeVee]

BlueBee - I rigged this up myself. I would need to check but I probably used a piece of 12g copper from a chunk of Romex. The battery charger gets it hot! The foam is easily cut as fast as you can pass by the wire. This is technology I learned in a machine shop back in 1970. Maybe I can take a picture and post here.

[BlueBee]

Very interesting post, PeeVee.  I think you’ve pin pointed a problem I have with my hot wire cutter!

My hot wire cutter used NiCr wire (from eBay) which has a higher resistance than copper and gets hotter with less current flow.  P = I*I*R.  NiCr is also the wire used in toasters and heating elements.  

Anyhow, my hot wire cutter glows red hot when running, but I used 22 gauge wire and not the thicker 12 gauge stuff you’re talking about.  That might explain a problem in my design.  

When I’m cutting at a slow pace, the wire glows red hot and cuts like a hot knife through butter.  However when I try to pick up speed, the heat from the wire gets sucked out too fast by the foam, the wire cools, and you can’t force the cut any faster or else you’ll break the wire.  With your thicker wire, it might be less prone to lose heat to the foam and hence let you feed stock at a much faster rate.

What happens with your cutter if you don’t feed the foam through at a constant speed?  Do you get a variation in the kerf of the cut?

[boca]

I also use a NiChrome wire to cut PS. It is 60cm long, so I can slice even parallel to the surface.
It works with both low density PS (isolation board) and high density PS (100 kg/m3 ready made beehives). HDPS needs a higher temperature (almost red, visible only in complete darkness).
To calculate the length/voltage/temperature, I found very useful the info at hotwirefoamcutterinfo.com especially the calculator page.

What happens with your cutter if you don’t feed the foam through at a constant speed?  Do you get a variation in the kerf of the cut?

I manage to get a fairly smooth surface manually.  However it requires a constant speed to move. Maybe I will make a simple board moved by two threaded rods, driven by stepper motors at a constant speed (probably never gets to the top of my priority list).

[Bee-Bop]

Not being the sharpest tack in the box !!

In the above posts no one has mentiomed what size/type saw blade is used  !!

Bee-Bop

[windfall]

 Foam being foam...no fiber orientation and super soft...I don't think tooth type or number will matter much. Size blade will be irrelevant unless you are cutting 3+" thick.

[BlueBee]

I agree with Windfall.  I happen to use a general purpose Freud 10” 40 tooth Diablo blade for most everything I do on the table saw.  They’re thin kerf and readily available at my local hardware store.  I’m not a fine wood worker; the Diablo is good enough for my crude work.

BTW…. BeeBop, thanks for the waxing tips a while back for coating the PF plastic frames.  I did exactly what you said and it worked like a charm.