I'm finally getting around to doing some work on my hot wire table. I have a design which minimizes resistance with minimal connections of smaller metal components. It's gotten a little into minute fine detail of the design with a lot of steps which has me thinking, am I'm over thinking/designing this setup. I've watched a lot of videos of different makes/designs on idiot tube and repeatedly see people attaching their hot working feed wire directly to the metal over head arm above the table top. By doing so wouldn't that drastically increase the resistance of the setup?
No because your still dealing with pretty small current and even though steel is a relatively poor conductor compared to copper, there is a lot of material so the resistance is low compared to the skinny resistance wire you're doing the cutting with. I don't even think I can measure the resistance in my steel arm it's so low. IMO, all you need for a hot wire is The right gauge resistive wire, A structure that can hold the cutting wire in the position you want and in spring tension so it remains so when it expands yet still remains taught enough to cut accurately The ability to control low voltage and generate the optimum cutting heat. You just need to use a low enough voltage source that it's not a shock hazard and it doesn't matter if it's AC or DC. Mine is just a step down transformer and a dimmer switch running on 120vac into the transformer primary. I take it you've been here: http://jacobs-online.biz/power_supply_design.htm Best, Kelly
Thanks for the reply Kelly. My HWFC is a double miter setup. The works include a RC speed limiter, digital readout, ac/dc transformer (100-240V- 108A 50/60Hz) (19V - 3.42A) inline fuse, and a On/Of switch w/ a active light. Capable of achieving very high temps if ever needed. I also have an assortment of Kanthal wire. No I haven't been to that website but will just to make sure I don't end up electrocuting myself.
You just need to experiment with the heat that suits the material your cutting and your desired cutting speed. You want it cool enough that you load the wire but not so hot it creates melt puddle and an unclean cut. If you dwell with any level of cutting heat it produces cut defects. They really help cut down the dust and mess when re-sizing and profiling. It gets a little trickier when you use thick gauge wire for profiles that can hold their shape while cutting. Best, Kelly
I started out using a battery charger and now I use a 5 volt DC computer power supply. I have a variable resistor I use if I'm trying to be real accurate in my cuts. I don't use it to just cut blocks or trim up some parts but I have to move quickly or it melts more than I want. Cutting foam is very addictive almost like popping bubble wrap. I just take big pieces of foam and turn them into little pieces.
Surfing the net I ran across this chart others my find helpful in regards to electrical conductivity/ resistivity of different metals. http://www.tibtech.com/conductivity.php
I use a battery charger and vary the temp by adjusting the connection point on the nichrome wire. Pete
Hey David and Kelly, What do you 2 think about making a sticky under the LF casting section and adding the above info links on hot wire foam cutters and the metals which give the best results for construction?
I used a cheapy rotating light switch dimmer to control my foam cutter. Then it pulls double duty on my soldering iron for wax work. Hey John.... KISS. Keep It Simple Stupid
It doesn't have to be fancy. An old school battery charger and a light dimmer work great for me. I find a clamp on amp meter crucial for setting the current and repeatability.
You guys still don’t get it. Sincerely, OCD I’ll be using mine for more than just cutting piece for casting. Hence, why I’m going to the extreme in building this contraption. PS No, my parents didn’t have any children that lived. We’re all brain dead.
Cactus, is that thick pink foam in your video laminated to thickness or did you buy it that thick? If the latter, do you recall where you got it? I can special order the Owens Corning stuff in 4" thick 4x8 sheets at the big box stores but I haven't put that to the test yet. Best, Kelly
Talked to David and think stickies are a possibility here at HF but we don't want to get carried away with them. We can unsticky them if so but let's see how the thread develops. Right now all of the posts in the entire sub-forum still display on a single page so not much need for a sticky. There are only a couple threads on such and they both readily come up upon searching the term. Best, Kelly
