With all the foam work I’ve been doing I decided it was time to do something about dust control….the stuff gets everywhere. I decided to build a hot wire to rough cut patterns and resize planks and build a dust collection system for my overarm router. This thread is about the hot wire build. I added the dust collection system to my machining XPS thread here. http://forums.thehomefoundry.org/index.php?threads/machining-xps-foam-patterns.14/#post-1717 A year ago I bought a small transformer, three 10’ lengths of 24ga, 26ga, and 28ga 60/40 NiCr wire and I finally got around to building a hot wire. I borrowed a few ideas from a hotwire I saw while surfing around eBay. The eBay unit was $230. It had some nice features but looked pretty flimsy. I’ve got $35 into this one. I fished the bent 1” steel arm out of the scrap bin at work and had the positionable handles left over from an old project. The main features I borrowed were using the metal arm as part of the electrical circuit, the spring tensioner, and the wire spool. I added the insulated support arm to support and stiffen the wire. I just used some castable refractory as the insulator in the support arm so the length of resistance wire in the electrical circuit remains unchanged by the position of the support arm. You can move the wire support on the arm to make angle cuts and store wire on the spool to compensate for the change in length. The spring keeps good tension as the wire heats and changes length. The spool of wire is just convenience. For the power supply, I just used a dimmer switch in front of the transformer and get 0-9vac. I fused the 120vac input ahead of the dimmer at 5amps. The wire is 20” of 26ga NiCr. At 9vac it produces about 600f according to the Jacobs calculator. Best, Kelly
Looks good. The overhead eyelet will help keep the wire straight. Have thought about adding a couple ceramic eyelets to the top and bottom of mine. I find a digital amp meter indispensable. I use a clamp type. Even if your connected NiC wire length or voltage varies, the amps tell you how much heat and can be dialed back in exactly. A difference of as little as 1/4 amp can make a hue difference in how it cuts.
Funny you should mention that. My power supply is just a throw together right now. After I use it for a while I plan on making a more permanent version with enclosure. I do have a panel meter, the same one I put on my electric furnace, and it reads voltage, current, power and energy. My multimeter just failed and I ordered another one with the clamping current probe. My transformer is dual tap so I'll wire it to be selectable for either 12vac or 24vac. At present, I can only measure 10vac at full dimmer. At 9v it should be 600F but even at 10vac it still seems a bit on the cold side to me. The cut looks nice and clean though with no discoloration. Best, Kelly
I also ended up throwing together a hot wire when I started using a template for pulley sheaves. A 1/2"MDF table, 1x3 sides, 3/4 plywood cut in an arch for the arm. I used a piece of angle as an adjustable head to allow for squaring. My son gave me a broken guitar string and I wired it to an old model train transformer. I added a spring on top for tensioning and as a quick release for internal pattern cuts. I went with a 12" clearance should I want to attach a fence for reducing thickness. I was a bit concerned that the wire would bow with that much exposure, but if I don't rush pushing material it has no problem.
I like the quick release for internal features. Makes me think in the future, I might consider ditching the spool of wire and move my tensioning spring up to the arm for better accessibility. I'm using mine but still tuning and messing with it. It takes a pretty steady hand and you cant dwell on your cut line due to penetrating melt. I haven't tried a wide cut to resize plank thickness yet. Best, Kelly
Made some updates to my hot wire. The first was to make a box to house and mount the power supply. When I built the hotwire I just grabbed what I had on hand and mounted it to a separate board. I had originally thought I could use the power supply for other things but I’ve never used it for anything else in the 2 ½ years since the original build so I figured I wasn’t missing out on much. It was a PITA because I always had to move and disconnect two things. Now it’s out of the way but still easily accessed. I used to have a spool of NiCr wire here. In 2 ½ years I’ve never once drawn wire from the spool. I removed it and installed a wing nut to clamp the wire. This allows for it to be quickly removed and reinstalled to make interior cuts similar to Chancre’s set up in post #4. After clamping the wire with the wing nut the clamp can be positioned on the arm to tension the wire. The spring is in the same position under the table. I made a lower guide eyelet and installed it flush with the table surface and reduced the hole diameter in both eyelets to closely fit the wire diameter. This reduces deflection and maintains the wire position more accurately. This coupled with wire tension and setting the height of the upper eyelet close to the stock thickness makes for much more accuracy, especially for pattern cutting. I use 1/8” tempered hard board (some call it Masonite) for patterns. The wire is <600F and if you don’t dwell, it holds up just fine. I got tired of clamping my router fence to the table so I made a dedicated fence. The only thing missing is a status light. It was too much trouble and I always unplug it after use. It’s all just refinement but makes for a better performing tool that’s quicker to set up and store. Best, Kelly
I drilled a hole in the table saw for a teflon flanged bushing that the wire passes down thru. Metal tube upright with a base plate clamps to the table. Some holes drilled at slight angle downwards that I insert a fiberglass driveway reflector shaft which acts as the top insulator and a spring. A screw lug clamps the wire and the bolt hole goes over the fiberglass rod and sits in a groove to locate it. Use the rip fence already on the table. I have a variac but it is too twitchy without another transformer to cut the voltage down.
Very neat. Just so I'm getting this right, the support rod is actually carrying the current and doesn't get hot because of lack of resistance, but is sufficient to carry the current to the wire which does get hot. So the whole thing is basically electrified, but low voltage makes it ok. It's not real complicated but I surely never would have thought of it. Pete
The cheaper the better. https://www.amazon.com/Newhouse-Har...sformer&qid=1586837876&s=instant-video&sr=8-7
I made one... Only thing I ever cut out on it was YOUR BP! I robbed the transformer off it when the one in my house died last year. The board now collects dust in the attic. Those of you with normal doorbells have a transformer hiding in some closet someplace.
Sometimes it's not it always what it looks like. Fit, finish, size are some other good attributes to be considered. Anything that has been personally customized usually takes on irregularities. Something about don't look a gift horse in the mouth... and if the shoe fits wear it. Pictures. We all like pictures.
That's correct Pete. It's 9 VAC at max dimmer setting and the current is low, so even though steel is a so-so conductor in electrical terms, there's plenty of it there in that 1"tube (.090 wall) to do the job. At 9 volts there is no shock hazard. Now if the transformer shorts through the windings, it most likely would go open circuit. If it did not, only briefly, the hot wire would quickly fail open, but the tube would be electrified. It's also fused at the source. The chances of shock are remote to say the least. I used a these guys and recommend them. Here's their how to: https://jacobs-online.biz/power_supply_design.htm They've been around for quite a while and cater to all the foam hobbys like sculpture, model rocketry and airplanes, cosplay, etc. Even though it's low power, it's enough that not any old dimmer won't do. It needs to be a slightly higher power version but still commonly available. Their kit saves the hunting around for transformer and suitable dimmer and then you can select your preferred wire. Have a look at their information tutorials on component selection. Even with something a simple as a hot wire has some nuance things that make a difference. I bought their Catalog# XFR0204E transformer and dimmer. Second one on this page. I also bought 3 wire gauges. They are very reasonable on small qtys and have a good selection of resistance wire. https://jacobs-online.biz/transformers.htm In my opening post I said 12vac but it's actually 9vac max. I fixed that. There's no reason to rectify it for simple resistive circuit. Model train transformers make good power supplies. You can even use a battery or battery charger but lose the ability to regulate unless you want to build a switching power supply. Lot's of transformers will do the trick as long as they can handle your amperage which may be as high as 3-4 amps. Not Kanthal. You can use it but it's actually not the best choice for a hot wire. You don't need the higher temp capability of Kanthal. You wan't good high resistance at very high strength. Rene' wire is actually the most desirable for a hot wire. You can read about is here. https://jacobs-online.biz/rene_wire.htm I have a lot of tension on my wire. It deflects that 1" arm over 1/2". The insulating eyelets allow you to vary the support length without changing the resistive length of the resistance wire. That tension and the close spacing of the eyelets limits wire deflection and makes for an accurate good performing cutter. I cut at a fraction of 9 vac most of the time and only use full power for very thick cuts. Like cutting anything, it's about feed and speed. In this case, cutting speed is voltage 9 (well, actually it's current but in a fixed resistance circuit voltage is proportional to current). When you reduce voltage it gives you much better control of your cut. I just dial it by feel. It's easy to do and altogether makes a huge difference in quality of result. Best, Kelly
Quick and dirty was my approach, a car battery charger and let the nichrome hang out the bottom, use the clamp to move it up and down the loose few feet wire to 'regulate the heat'. I'd favour doing a proper set up but it worked for me.
My sad little benchtop wood working bandsaw works pretty good for cutting out foam shapes. I make cleaner straighter squarer cuts with it than I ever did with my old busted hot wire table. So for a while I have been considering rebuilding it (not the bandsaw, the old hot wire table) into a horizontal hot wire table, for cutting slabs of foam to a desired thickness, rather than vertical for cutting out shapes. Jeff
Really? The quality of cut on my hot wire is far superior to any band saw blade I have. In fact, the only cut that may be better is that from a spiral multiple flute carbide router bit at 20krpm. Maybe a very sharp razor with a lot of rake and slicing action. Beyond that only finely sanded surfaces can be better. .....Me thinks Tobho Mott needs to hone his Valyrian wire sword to a finer edge! If the vast majority of what you would cut is resizing the thickness of foam plank, horizontal may be ok but otherwise, I would keep the wire vertical. The majority of what I do is resizing and cutting blanks/profiles to be machined and my fence is tall enough to easily cut a 10" plank to any thickness desired. Most of the time I don't even clamp the fence.....just hold it in place with my hand while I guide and cut the foam with the other hand. Best, Kelly
It never did work as well as I expected it to, but I always thought I could improve it if I ever got around to tinkering with it more. Likely would have made a point of it if I had space to keep it set up all the time. The little bandsaw doesn't flex as easily as my hot wire did and its cuts are easier to sand smooth because my hot wire left some hard crusty spots sometimes. It won't cut a straight line OR a curve in 1/4" plywood when you want it to, but it does ok for me in XPS. Just found out yesterday it works better for cutting gating off aluminum castings than for cutting wood too. Slow going, but nice. Jeff
