Hot Wire Foam Cutter

Someone had posted a nice and easy set of instructions for a 12V wall outlet type hot wire cutter using lightbulbs, etc. but it’s been removed from the discussion board. I just need to know the placement of the bulbs along the electrical cord and how to hook up the dimmer switch. I’m a pretty smart person but electrical stuff is lost on me. Maybe a simple line drawing would be in order. Thanks for any help out there. Happy holidays n’ drive safe

You could do it the old-fashioned way using nichrome wire and an electric train transformer.

Yes, but those train transformers are not as plentiful as they used to be. I scour the flea markets every weekend looking for them

Sounds like you could use any old DC converter - those little wall plug adapters with the boxy plug (that you see on answering machines or other small electronics). Then go get yourself a hevy duty potentiometer or rheostat… probably have more luck finding a rheostat that’s strong enough… try a Marvac, or Orvac, or anything else with a ‘vac’ in it. Just make sure you ground it… a quick blow fuse might not be a bad idea either.

They sell hot wire variacs at wicks.com. They cost about $120 and are a very nice piece of equipment. We are looking into selling them as well, possibly after the first of the year.

I just tried an eBay search for “variac” and got a page full of hits from hobby level low cost to whopping industrial size rheostats-- and that’s not really even trying very hard. There are obviously plenty out there. Of course, you could also pretty easily build an improvised rheostat with a long coil spring and a couple of sizable alligator clips. Make sure it’s insulated pretty well and experiment to find your target voltages and you could just solder up a permanent tap at the sweet spot for each wire size/length of cutter. If you get electrocuted, then this wasn’t the career for you anyway. ;^) -church

I have the train switch. Now what? Just hook up a wire with alligator clips? What guage of wire? What’s the next step?

You can generally get blocks of foam locally from insulation foam suppliers. The rocker templates are made from 1/8 inch masonite. They are attached to the block with nails and you then slice the foam with a harp, strung with a piece of nicrome wire, that is powered by a variac. A variac is a voltage regulator. For the foam, look in the yellow pages under insulation and look for a supplier of foam. Almost every major city has at least one. For the variac, they are available from Wicks aircraft. They have a nice voltage regulator for hot wiring for about $100. I think they also have wire. We use 25 guage nichrome. They have an online catalogue at www.wicks.com. The harp is just a piece of plywood cut in a U with the wire strung across the open end. It has to be wide enough to fit across the foam your cutting and deep enough to cut the thickness of the blank. Give yourself lots of room on that one. Ours is about 16 inches deep. You attach the voltage regulator to each side of your harp (we use alligator clips), turn the regulator up to about 25 volts and your ready to cut. Set the wire on the templates that are attached on either side of the foam block and push the wire slowly through the foam. When you finish the deck, hook the wire under the templates and pull it through the bottom. It helps to have a fan blowing down the block of foam to cool the exposed wire that’s outside the block otherwise that portion of wire super heats and you break a lot of wires. After you’ve cut your blank, set it on a shaping rack bottom up. Get a piece of hot wire long enough to reach the length of the blank and about 2 feet extra. Attach a piece of wood (these are handles) to each end of this wire. Now attach the voltage regulator to each end of the wire. Now you need to find the middle of the blank and mark it on each end. You need a friend to hold one end of the wire while you hold the other. Set the voltage at about 70. Stretch the wire from end to end on the marked center of the bottom of the blank and turn on the variac and slowly pull the wire from the bottom of the blank to the deck. You now have the blank cut for the stringer. You need five bar clamps to glue up with. For a stringer you can use 1/8 or 1/4 inch Luan plywood which is available at Home Depot. This stuff doesn’t shape great but its easy to find and works. You can also use 3 mil PVC which comes in 4x8 sheets and is available from sign supply companies. Comes in colors and looks great. For gluing Luan you can use good old Elmer’s glue. For PVC there is a glue called Roo Glue that works well. You can probably find that on the web. When you glue up, you wet both sides of the stringer and both sides of the blank, line up the parts and then bar clamp it together. And that’s about it.

Hook up the light bulb to any light socket fixture and wire it somewhere on the cord between the wall outlet and your loom. Cut one of the wires and attach both ends to the socket, one on each terminal (make sure the cord is NOT plugged in when you do this!)You can cut the hot or neutral wire. Gary Geist

pretty much, yep… you need both copper wire and nichrome wire in addition to those alligator clips - use http://www.wiretron.com/nicrdat.html to get the appropriate size for the length of nichrome you want to use,given your transformer and so forth. I have also used a big doorbell transformer very successfully. A variac is the best setup, no doubt. You might also be able to take the guts out of a clapped out soldering gun. Bear in mind that melting it’s way through a chunk of foam cools it off considerably, so calculating wire sizes you might go up a temperature range. Other considerations- very thin nicrome tends to stretch as it heats and goes through foam. And when it does, the wire itself gets thinner, which means it heats up and stretches more, which eventually means your wire can part on you. Good idea to go lightly on the pretensioning. Work in a ventilated area - foam fumes are not exactly the scent of rosebuds. Careful of ‘dragging’ around a curve - the wire bends and you don’t get a nice straight line. hope that’s of use doc… http://www.wiretron.com/nicrdat.html

Mr. Loehr, could you please tell all of us exactly how you make your epoxys. Step by step now, please don’t leave any little thing out. We would like to get into the epoxy manufacturing business, and this is the perfect place to find out everything that we need to know about everybody elses techniques,formulas, and results. Thanks in advance, as usual. P.S we really only want to waterproof all of our styrofoam swimming pool kickboards for next summer. We figure that with all of our allowances pooled togeather, we should be able to offer epoxy with our own label too, and some coated kickboards as successful samples of all of your detailed instructions. Thanks again, Mr. Loehr

Success! Cheap man’s hot wire cutter is now completed and working. Two 250 watt lightbulbs seem to create the perfect juice flow when combined with whetever guage stainless steel wire it is that I’m using. Now, can anyone tell me once and for all, IS EPS really closed cell or open cell? and how can I tell the difference between extruded and expanded foam (if there even is one). The only foam I can buy locally is the blue, polystyrene dock billets and I can’t seem to blow air through even a small slice of it.

Good for you… is that stainless wire or nichrome? Closed cell foam - think cheap cooler, lotsa little pellets of foam like a ball of cooked rice squashed together. Open cell foam is more like , well, Clark foam or the foam on top of a beer - a base material with bubbles in it. There is a lot of confusion between the two - the above is the industry definition. hope that’s of use doc…

My two cents. EPS -(Expanded Polystyrene) - up close - has the look little spheres of foam stuck together. when rough cut will rain little foam spheres. XPS - (Extruded Polystyrene) - up close - has the look of a resin or glue with tiny bubbles through-out. Looks alot like Clark (PU) foam but is somewhat more elastic and rubbery, whereas PU foam is more brittle. When cut you get dust, not spheres. Is the blue stuff Matt has XPS? Some confusion, for me anyway, comes from the fact that closed cell foam has more open voids to fill than open cell foam. Which just sounds backwards to me. The Kids should go home now. Eric J

Although EPS is beaded the EDRO machined EPS sands as smooth as PU. The cooler stuff will tear out. Gary Geist

matt, the foam in your coffee cup or wetsuit is called closed cell. the foam in your seat cushion, pillow, mattress, or polyester surfboard is open cell. the main types of foam you will come in contact with in daily life are ester, ether, urethane, styrene, and neoprene. your ester, ether, and urethanes are open cell. the other two are closed. the foam industry adds hardeners, and flame retardents, different foaming gasses and or agents. these additives affect the hardness, stiffness, rigidity, flexibility, compressability and flamability of the various foams. a dense foam can also be flexible and have limited compressability while a less dense foam can have the same compressability by adding hardening agents but it will be more rigid and, therefore, not as flexible. softer denser foams (especially polyester) are considered high quality in the industry because of their purity and are thus very expensive. styrene foam makes good coffee cups because it is cheap, light, an excellent insulator (i’ve seen expanded polystyrene coffee cups used to hold liquid nitrogen), and waterproof. i’m sure this fully confuses everyone. clark foam is a cheap foam with a huge profit margin. that’s good for grubby. eps is cheap too but you or anyone can buy the eps in bulk as greg mentions above and benefit from the savings. that’s good for everyone. plus with greg’s method you get a very square blank. not the twisted blank you can often get from clark which you have to straighten out first by removing foam or returning to the distributor, and good luck with that.

well then, what do you call wetsuit foam after it has been sliced on a cutting machine? what does the surface of those cells now look like? well then, what do you call a clark surfboard blank after you slice off the skin? what do those cells now look like? ring a bell!!! still closed cell foam with the surface layer sliced in half!!! mis-information, is worse than none to begin with. eh-s

Thanks for everyone’s insight on closed vs open cell foam. I thought I could tell the difference between the two simply by looking, and generally still think I can. The name basically says it all. HOWEVER, I’m not convinced that my DuPont extruded foam billet is open cell because while it looks open cell to the naked eye, it won’t allow air to pass through a freshly cut section. Also, wouldn’t dock billets have to employ some kind of closed cell structure to prevent the positive pressure from surrounding water to eventually penetrate, at any tempurature? I guess I just want someone to say, “yeah, don’t worry, that blue shit you bought is closed cell and will never absorb water”. Then I can sleep good at night. I only make boards for myself and all expenses are eaten my moi.

First you find all the information you can, Internet, books, industrial guides, etc., and work yourself through a reading program so intense that you basically wreck your eyesight. Then, as you begin to understand the processes involved, you begin making hundreds of small test batches until you come up with a basic working formula (this takes many months or even years). Now you muster up all your guts, and all your available cash, and sink it into numerous drums of chemical based on the guesses you made during the small batch process. Now you are ready to finalize your custom mix but first you have to throw away a significant amount of those expensive chemicals because big batches never come out like small ones. But that’s not all, I need to tell you that at this point you have to go back and start again because you just finished ONE HALF of your mixture. You still have to do the other half. After this ordeal you are now ready to make some boards! But first you have to throw away some of the first ones because you realize that you did something wrong during the mixing process. And then, after a time, as you realize that your mix has other flaws like discoloration from UV, incorrect modulus and incompatible hot coats, you get to replace a significant number of the boards that you did manage to sell. Also, you have to remember that epoxy doesn’t work just like polyester so the boards won’t come out quite the same and when you have the audacity to comment on the lack of quality you get to hear the glass shop employees tell you what a f*#kin’ idiot you are for forcing them to change and some even try to sue you. At the same time the leading urethane foam manufacturer is writing scare stories and circulating them throughout the surfboard industry telling everyone that you are going to single-handedly “ruin the surfboard industry” because your an “idiot” and then black ball you and some of your customers because they bought from you. At the same time others interested in stealing what little business you do have, try knocking off your formulas and then undercut your prices with inferior product, thus giving epoxy boards another black eye. Meanwhile, in the surf shops, any shop that doesn’t carry your product has a perfect opportunity to bad mouth yours because it’s “different” and no one should be allowed to be very “different” in the surfboard industry, right? Many shops will then refuse to take your boards on trade using the moment to again tell consumers that you an idiot and that they were fools for ever buying such a product in the first place. Other manufacturers will also chime in with this because they don’t want change and this is a perfect route around this most abominable outcome. Some will even publish longwinded rants about your evil doings. Still more will refuse to build the product because it lasts longer and they will not get as much return business. And then finally the day comes along when you meet swaylocks for the first time and you are able to tell some of the more knowledgeable in the industry your side. You get to dispel rumors, lies and untruths. You get to finally tell it like it is to people who are ready to listen. And on that day you finally get some measure of understanding and respect from an industry who has turned a deaf ear to you and your product out of fear and ignorance for over 20 years. And at that moment you get to decide if it was all worth it. So now you know how it’s done. Ready to start?

You paint a dismal picture Greg. However, I will never regret embarking on my mission to make a surfboard to ride. I live in Eastport, Maine, where most people have never even seen a surfboard, let alone a surf shop or supplier of anything resembling surfing. But with enough background in composite materials and various water sports, I managed to procure everything to make a sick little EPS/epoxy hybrid. Right from the fins down to the leash plug. 100% made by my bare hands with locally-supplied materials. After all the sweat, cuts, foam dust inhalation, and epoxy rash, I never once regretted doing it and was never happier when it slid down the first wave. So if the industry sucks, which most industries eventually tend to, there is at least some human, creative element that is more important. Money is junk anyway