There are more comprehensive posts along these lines but I just thought I would share my experience.
I found all kinds of posts about how to make a hotwire cutter from scratch using transformetrs and light bulbs along with soldering this and that but Im not very comfortable with electricity as Ive never taken the time to truly understand how volts, amps and watts relate and effect each other and what that means in terms of safety for a person making a hotwire cutter.
The best (read simple) guide I found said the most important feature is that your hotwire cutter should be LOW VOLTAGE as a first priority. The range of 9-14 volts was given as a guide and amps of 1.5 to 3. But it didnt list any quick and easy ways to achieve this other than a battery charger. But what battery charger I have about 6 different types and this was a bit ambiguous.
What I found out is that a car battery charger without smart charge converts into a hotwire cutter instantly if you simply clip the crocodile clips onto each end of a thin, single filiment, metal guitar string. My car battery charger has 12.5v at 2.5 amps - perfect.
I tested the suitability of my charger/wire combination by connecting the clips to the wire, laying them out on my bench so nothing was touching anything conductive/flamible and turning the charger on. I then picked up the clips by holding the insulated handles so the wire between them was stretched tight and I did a small test cut (15cm long through 3" eps) and it worked really well - like butter. I now know Im not wasting my time building the frame.
serving suggestion:
Cut a U frame from some ply and tap a nail into each tip of the U
Wrap the wire around each nail leaving a little excess (10cm or so)
use cable ties to secure your chargers crocodile clips to the arms of the U
connect the crocodile clips to the excess wire at each end of the U
Plug the charger into the wall and flick the switch
Another variation a I saw was a frame made from PVC plumbing pipe with all the wires and clips running inside the pipe so the only exposed item was the hotwire - great idea and I’ll probably do this as it also means you could have several lengths of pipe on hand and use like lego to change the geometry of your cutter for different tasks (ie make it smaller for rail bands or bigger for rocker cuts.
Anyway…
hope that helps someone trying to find out where to start with hotwire set up - car battery charger and a guitar sting - easy.
I should have mentioned that I have not done any serious cuts with this - only the test cut mentioned…
I plan to do a few more tests once I have my frame built and everything set up.
I suppose the object of the above exercise was to test if I had the right idea using the car battery charger as this was the most elegant solution I could find.
I really didnt want to be cutting and soldering wires or starting the build from scratch as I dont think I’ll use it enough and I just want to start shaping.
I’ll stop past the electrical supply place and pick up some better wire to do some tests with.
I use fishing leader wire from Walmart or Academy. It’s a stainless nickel/chrome alloy and won’t stretch much when heated. Carries current well and last a long time. Just run something like a hard piece of plastic across the wire after each cute to clean the residue off. The thickness I use is .018 dia. and .022 dia. The brand name is Malin from Academy, and Mason from Walmart. Both work equally well and are cheap. The commonly called nichrome wire gets hotter I think but I’ve found it’s much more brittle and subject to breaking when heated and streatches too much as well. Oh and the stainless safety wire used in the aircraft industry is the worst wire to use. Very soft when heated. I’ve broken it many times when I didn’t have anything else around and was trying to make a cut. Don’t use it unless you just have to take the risk.
I also use a 10 amp battery charger so I can heat a longer wire and control the current with an adjustable ceiling fan switch. I mounted one into one of those blue double wall plug boxes and connected a wall plug and ceiling fan switch together with a replacement lamp cord from Home Depot. Takes 15 minutes to make if you have the parts. You can adjust the current by simply adjusting the ceiling fan speed control and it also works to turn power on and off as well. Been using this for years now.
For a bow I made one using galvanized electrical conduit and bent it into a bow shape with a tubing bender. You can do it on a vise if your careful. I used ceramic electric fence insulators on the ends to wrap the wire around. You can get them at Home Depot or Lowe’s. Just drive a wooden dowel into the ends of the conduit after its bent and use sheet rock screws to hold the insulators on. The springiness of the conduit holds the wire tight when heated and helps to prevent wire lag.
The main thing to getting a good cut is light steady pressure. Adjusting wire temperature so you just get a slight sizzle sound as it moves through. You want it to melt the foam and not cook it. If it’s turning black the wire is too hot. Good smooth templates and letting the wire do the work and not getting in a hurry will take care of the rest.
I use fishing leader wire from Walmart or Academy. The thickness I use is .018 dia. and .022 dia. The brand name is Malin from Academy, and Mason from Walmart. Both work equally well and are cheap.
Just went to Wally World and all they had was nylon. Went to “outdoor” shop and they had uncoated wire leader but only rated in pounds. No diameter given. I got 40 pound and it barely warmed up. Any idea what the above leaders would be rated in pounds?
Also, I have a 12 volt 6 amp battery charger…enough to drive a cutter? Or am I needing MORE POWER?
–Stand back, rookie electrition who at least knows what not to touch and how to pull the plug if it starts to smoke!
My battery charger is 10 amp. at 12 volts. It will heat a wire pretty well up to about 2 feet in length. Anything longer than that and you will need a larger one. At 6 amps. you may still be a bit small. The Mason brand .018 dia. is 69lb. test chrome nickel alloy stainless leader wire. The .022 dia. is 105lb. test. They can be pulled pretty tight when hot without breaking.
Thank you. I definitely am under powered then. I got some 40 lb and 2 feet gets barely warm enough to tell that it is warm. Oh well, a free power source was a nice idea.
My $.02. In my lack of knowledge I bought a Variac @ 1.5 amp off ebay… blew the fuse every time before getting warm. Got two different car charges, but they were to fancy and wouldn’t work with out a batteries feedback. The “Pro” I saw in action was using a 10amp Variac, and was doing 10’ center cuts @ 50 volts.
I guess I’m looking at going back to ebay and applying my new gained, and not cheap Ha!, knowledge.
One thing I thought of - Saw the “Pro” heading this way to. boght 2 blocks 8’x11"(width)x16" (about 5 boards thick) - The theory is, the machine cut is perfect, and I’ll only have to cut rocker and foil into less than a foot - easy to manage alone, and no center cutting to do either.
Yeah, the car charger kind…automatic needs battery feedback and has uncontrollable variable output. The manual kind just belts it out at full volume all the time. Likely that kind would work.
Contemplating on way to work…I know zip about electricity but I think it is the Amps that is key. Lowish voltage not a big deal, its the amps that heat the wire???
Hard to get one (amps) without the other (volts). Here’s how they are related:
Volts = Ohms X Amps
To get a wire to a certain temperature, you need a certain amount of amps. To get those amps, you need volts.
So, if you know the resistance (Ohms) of the wire, and you know how many amps you need, you can then figure out how many volts you need to get the amps to cut the foam. Then you just dial that voltage into your variac and go. Most people (including me) just do it by trial and error, finding the voltage setting you cut best with.
Some wires have more Ohms per foot than others, so each wire will have a different amps setting it will cut best at. As far as I know, car battery chargers self-adjust voltage (or it is set up previously by knowing the internal resistance (Ohms) of the battery) to get the amount of amps they need flowing into the battery. That’s why 12v battery chargers have amp ratings.
Hard to get one (amps) without the other (volts). Here’s how they are related:
Volts = Ohms X Amps
To get a wire to a certain temperature, you need a certain amount of amps. To get those amps, you need volts.
Sorry but this is a bit off. The equation is Watts = Amps X Volts. So if you’re putting out 6 amps at 12 volts you’re dissipating 72 watts.
The resistance of the wire goes to how much current is allowed to pass in a given time. Basically the wires you’re talking about are fairly low resistance wire so they pass most all of the current.
Watts are a measure of power, Voltage is the force and Amperage is the “mass”.
What it boils down to is you can get the same work (in watts) from 6 amps at 12 volts, as you can from 3 amps at 24 volts, etc.
You are correct, but both equations are valid, depending on circumstance. V=IR (Volts=AmpsXOhms) is Ohm’s Law. What you are talking about P=VI (Watts=VoltsXAmps) is the power equation. Power is Joules/second because Volts (V) are Joules/Coulomb and Current (I, Amps) is Coulombs/second. The Coulombs (unit of charge) cancel out when you multiply Volts x Amps, giving you Watts.
Ohm’s Law has to do with resistance, which is not taken into account in the power equation, unless you use Ohm’s Law to backtrack.
If using stainless steel wire, yes, resistance is very low, not the case with resistive wires like nichrome, which is what I use for cutting…
Either way, in order to get a current through the wire, a voltage must be applied. By Ohm’s Law, a current will flow through that wire. For every voltage across the wire, a current will be generated. For a given current through the wire, the wire will attain a certain temperature. Power for each case can be calculated with the power formula, but in my opinion, it is not the place to start, unless you are using a wire with such low resistance that the only way to control temperature is to control current, because any voltage applied will result in a giant current (due to the very low resistance). Nichrome wire has a set value of resistance per foot, so I start with voltage. For stainless steel wire, I would try to regulate current instead, by different means (probably a transistor if a DC circuit, or no need for transistor if using a Variac w/ mains power).
Two ways to explain the same thing depending on the type of wire you are using is all…
Me and my buddy Tim are using a 12v 5amp charger with a 2 foot bow with a 12gage top E guitar string, it does work but it is a bit slow. We tried a 10 gage string but this was crap. You do need to be patient with this set up and not pull it as the string will ping.
Very nice summary. I was trying to make it simple for those that didn’t know much about electricity.
This is a very interesting subject, as I have been out of shaping and glassing for some time. It’s good to see that smart people are making things better all around.
I am a kook shaper at best, but the hotwire and router make for easier ways to get the rocker and outline you want if you are like me (artistically challenged). I don’t think I could shape polyurethane blanks well at all, having to dial in the rocker by hand… If I want a slightly different rocker, I screw/pin my templates into the side of the foam block with a little bend in them up or down, and you can get lots of variation that way, without having to touch the planer at all, just depends on where you screw/pin the template in first before you start bending…
Let us know if you make yourself a setup, and how you did it; I can always stand to learn something new, as everyone has a slightly different approach to things…also, if you get stuck somewhere and have a problem, this place is great for getting great ideas on how to solve it…
