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If you have no means of cutting your polystyrene other than a messy craft knife and can't justify forking out for an expensive hot wire cutter, try this.

Get a cheap, bog-standard soldering iron available from any hardware store (or ebay - that's where I got mine) and some domestic mains flex [pics below]

Pull a strand of the copper core from the flex and fix it to the soldering iron with the screw used to secure the solder tip. Wind the copper strand around the solder tip and vois las! A hot-knife for less than a tenner.

This'll slice through your polystyrene no problem and thinner copper will help you with the more detailed jobs.

SAFETY NOTE:- Polystyrene fumes are toxic so ensure your work area is outside or very well ventilated. Also, soldering irons are hot so please don't be a dick and lay it down on the nylon carpet or your leg. If you are too young or simply lack the mental agility to realise on your own that melting plastic produces fumes and hot things hurt when applied to your skin then I strongly suggest you don't try this...and if you do, I take no responsibility for the resulting inferno.

Also, please be aware that I am an adult (legally at least) and already proficient with a soldering iron. As such I know, for example, that the model of iron I'm using is suitable for this task and that the modification in no way compromises the grounding or other electrical fidgy-widgyness that would normally make the tool safe. If you're unsure that an iron is suitable, ask someone and if you have never used a soldering iron before, get instruction. And if you are going to have to borrow your Dad's tools, make sure he knows what you're up to and is ok with it.

What i could use is a good method to cleanly cut high density polystyrene aka hard pack wall insulation.

This'll work on insulation too but as for a "clean" cut - ie. without any imperfections at all - the only thing I can think of is a modeling knife and a lot of patience.

heard there is some sort of hobby cutting laser out there, people that build up scale models for architects have em. someone here on dakka dakka mentioned it along time ago, but it sounded like an expensive way to get precise cuts for styrene.

Please be aware that the fumes given off by melting polystyrene will severely feth up your sinus' for about 2 weeks. It is very much not good for you. Do this outside and wear a mask.

This seems a bit brutal, I still recommend a hot wire cutter it's more elegant and clean.

The benefit I see here is that you can custom shape the copper wire to make different cuts, which with extruded polystyrene would be fine.

aerethan wrote:Please be aware that the fumes given off by melting polystyrene will severely feth up your sinus' for about 2 weeks. It is very much not good for you. Do this outside and wear a mask.

Ah, yes. Apologies to everyone for not including some safety advice. I have now amended the original post with a safety note.

Howard A Treesong wrote:This seems a bit brutal, I still recommend a hot wire cutter it's more elegant and clean.

Indeed a hot wire cutter is designed for this task specifically but in principle there is no difference in the two tools (it's nothing more complex than heat passed through a conductive wire ) other than you can adjust the temperature on some models of wire cutter and they heat to a higher temperature. Be aware, though, that the hotter the wire, the more sure you have to be with your cutting as you have to be quick and any imperfections in the cut will be twice as obvious. On the other hand, too low a temperaature is time consuming and messy. You will have stringy crap coming off the polystyrene no mater what (just sand them off lightly with fine wet & dry paper) but if the wire is too cool it's nightmarish. I've simply found the soldering iron idea is a nice balance between the two.

This is only my opinion, which I've come to through experience but in the end the deciding factor is your own individual skill.

aerethan wrote:The benefit I see here is that you can custom shape the copper wire to make different cuts, which with extruded polystyrene would be fine.

Indeed but you can do this with purpose built cutters too. Although the wire is normally looped (so the heat doesn't dissipate toward the tip) on these but there's nothing to prohibit you from trying different shapes. Just make sure the bugger's off first

Dax415 wrote:heard there is some sort of hobby cutting laser out there, people that build up scale models for architects have em. someone here on dakka dakka mentioned it along time ago, but it sounded like an expensive way to get precise cuts for styrene.

This sounds so cool I might cry but I reckon if you can afford a laser capable of cutting anything at all, you can afford lackies to do it for you instead.