hot wire cutter theory

General Discussion
21

Hi Hunty!

I would say it´s a tricky thing to try discussing a practical design for a Hotwire on such a theoretical level. Eventhough i for myself really like every thinking in that overall direction, and am prepared to talk about the coulomb laws, the three kirchhoff laws and the movement of free electrons within metalbonding etc., i don´t believe the basic laws of physics will save you from making big mistakes if you fiddle with your fuseboxes at home for example. In that sense i´d say doc has given very good advice on the practical side, and was probably just simplyfiing the physical background in order for everybody to get a basic picture. Naturally the flaws get in there, but it´s no use discussing those. doc is right in pointing out, that the maximum amperes limit your system rather than the voltage. This is because we are talking about a metalwire here and not about something unconducting like for example air, which requires a minimum of 40000 volts per meter to get conductive.

Just put a big screwdriver between the poles of your car battery and watch it glow white in a second throwing sparks, if you think 12 volts are lame.

maybe the simplest way to go for you, is to take your bow and change one end, so you can push the main cable alongside your wire, to alter the length of it´s hot part. But you have to make sure, that the connection has enough contact, because otherwise it will be your hotspot (as doc has already explained). you could curl it around,if it´s a solid copperwire. This way you can adjust the temperature, try it on the foam, and see if the remaining lenght is enough. If it is not you could use your car battery for short term maximum power, for it has way more amperes than the charger.

Anyway as a kid my modeltraintransformer did hotwire the foam for a modelkatamaran very nicely, after i burnt lots of wire and my little fingers anyway. Later in the project i was horrified, when the paint dissolved my hard work.

regards - d.

22

5 amps will do it

but between 6 and 7 amps at 13 odd volts

will whip out a blank in a very short time ( few minutes perside)

nichrome can cut when its red hot

but i back it off so its not that hot

i get perfect cute regularly by hand with out assistance

nichrome and a variable power supply

i know its an extra cost but it will save a lot of drama

those power supplies do sell on trade me for cheap sometimes

23
Quote:

Hi Hunty!

I would say it´s a tricky thing to try discussing a practical design for a Hotwire on such a theoretical level. Eventhough i for myself really like every thinking in that overall direction, and am prepared to talk about the coulomb laws, the three kirchhoff laws and the movement of free electrons within metalbonding etc., i don´t believe the basic laws of physics will save you from making big mistakes if you fiddle with your fuseboxes at home for example. In that sense i´d say doc has given very good advice on the practical side, and was probably just simplyfiing the physical background in order for everybody to get a basic picture. Naturally the flaws get in there, but it´s no use discussing those. doc is right in pointing out, that the maximum amperes limit your system rather than the voltage. This is because we are talking about a metalwire here and not about something unconducting like for example air, which requires a minimum of 40000 volts per meter to get conductive.

yeah i completely see what your saying,but the reason i started the thread was because the other ones i read seemed to be very practical orientated all ready so i thought it might be good to get something going that digs a little deeper for those who want to talk/read about it.for me something like this is a bit more of a help cause if i dont think that I have it clear in my head about what im doing and why before i start.it makes me much less confident in doing it.and any info exchanges that help get it clear in my head i am grateful for.Some of the points doc has brought up

i hadnt grasped before and may have led to me making something that would not have worked quite right.

Quote:

Just put a big screwdriver between the poles of your car battery and watch it glow white in a second throwing sparks, if you think 12 volts are lame.

i dont think 12 volts are tame im just not sure that using 12v on my cutter the way it is and going and buying something to limit the current will definately work so i am not confident to go that way unless i have it making sense to me upstairs.

anyhow cheers for the input, its keeping things ticking over upstairs in the cheese factory.

james

24

sorry, i didn´t really listen to your headline then… I thought it was only about an improvement of your wiretemperature. I posted, because doc´s correct advice seemed to get lost in a lot of circuits,waterpipes and wireology.

i´ll try to help with simple thoughts:

doubling the votage will create exactly the same wiretemperature, than taking half the length of the wire. The current is proportional to both.

when the wire starts to glow it´s resistance increases a big leap. so it stays at the temperature quite stable, since the radiation needs much energy.

fancontrolls and other stuff applied to the circuit takes away some of the energy.

cheers - d.

25
Quote:
i´ll try to help with simple thoughts:

doubling the votage will create exactly the same wiretemperature, than taking half the length of the wire. The current is proportional to both.

when the wire starts to glow it´s resistance increases a big leap. so it stays at the temperature quite stable, since the radiation needs much energy.

fancontrolls and other stuff applied to the circuit takes away some of the energy.

cheers - d.

yeah this really does say alot with out actually saying alot.Improvement of wire temp was definately one of the things i was looking for, and to what temp and why was a part of that question as well.

26

Hi Hunty!

I´m not really sure, whether i understood your questions on the what and why of wiretemperature.

In the links that mtb and doc posted there is elaborate information on the meltingtemperature of polystyrene and a diagram for the temperature of nichromewires in dependence of diameter and ampereage. So that´s probably not what you mean. This is why i refered to a sort of “how” for increasing the wiretemperature.

So if you are not asking about the chemophysical backgroud on the collapse of polystyrenebubbles at contact with a glowing metalsurface or the glowing itself, what is your question aside from the practical setup?

I´d say the health issue might be considerable: The foam consists of a thermoplast (deforming under temperature) and also dissolves into oils and toxic gases if heated excessively, so the coolest melting possible, as silly does it, and a mask should be a good idea.

regards - d.

27

recommend ventilated and kept away for pregnant women

but nothing has been proven as far as i can tell

you get nausea after a cutting in unventilated room, after long exposure

you can reduce the amount of fumes by not cutting red hot

yes i use a fume mask

but it isnt to bad if its not smoking much

28
Quote:

Hi Hunty!

I´m not really sure, whether i understood your questions on the what and why of wiretemperature.

In the links that mtb and doc posted there is elaborate information on the meltingtemperature of polystyrene and a diagram for the temperature of nichromewires in dependence of diameter and ampereage. So that´s probably not what you mean. This is why i refered to a sort of “how” for increasing the wiretemperature.

So if you are not asking about the chemophysical backgroud on the collapse of polystyrenebubbles at contact with a glowing metalsurface or the glowing itself, what is your question aside from the practical setup?

yeah maybe i didn’t ask the question in a way that was clear and easily understandable.First thing that needs to be made clear is that i am on a budget so i only want to do it on the cheap(or cheap as possible).

So i made the bow and planned on just using my battery charger as ppl had said they had done on other threads,but when doing so it was not able to deliver enough power to heat up the wire.so that made me wonder why it wasnt working for me.so the first thing i did was measure the resistance of my bow, which after measuring the resistance of it was high i worked out that i was going to need more voltage for that bow as well as more power.

because i allready had a fan speed controller(the ones for ceiling fans)i thought no problem i’ll just buy a cheap transformer that has the right power rating to do the job and since its hard to get a transformer with the exact out put voltage needed i thought i would go for what ever is the closest one size up and just reduce my input voltage using the controller to get the current needed for the correct heat in the wire(i then found the heaters plus site with the tables on it).

Now is where i started to have a few questions as i didn’t actually know what the best temp was for cutting the foam which was going to make it hard to work out from the tables

of nichrome 60 wire on heaters plus, what current i was going to need, and on top of that i wasnt sure if the tables on the nichrome 60 wire were the same as for the nichrome 80 that i all ready had(i was unable to find the same info for nichrome 80).

So since im on a budget and the higher the power rating of the transformer the more expensive it will be, i want to be sure im not getting a size too small(which most likely would be usless and not work and id need to get another one)or a size bigger than i actually need(which would more than likely cost more).

so i thought i’ll start this thread to answer these questions, try to get as clear a idea as to what i am doing and why and so anyone else can talk in depth as they like about any aspect of the hot wire cutter/cutting.I also started wondering if there was any other aspect of the hot wire cutter/cutting that i did not understand that maybe i needed to, so i thought maybe i would pick up some other use full info along the way.And i have, and hopefully other ppl who find any aspect of it interesting will as well.

I hope that makes a bit more sense on what my questions were, as you can probably allready see english and expressing myself are not things im terribly good at which is probably why my question isnt very clear.

BTW “the chemophysical backgroud on the collapse of polystyrenebubbles at contact with a glowing metalsurface or the glowing itself” sounds interesting, feel free to elabourate if you have the time, sounds like it might be a bit over my head but it does sound interesting.

cheers

james

29

i missed this post sorry burnsie but that is somthing that never even crossed my mind, definately worth following up and comparing prices with the transformer.

cheers

James

Quote:
Get yourself a 24v battery charger, that will sort out the heat problems
30
Quote:
nichrome and a variable power supply

i know its an extra cost but it will save a lot of drama

those power supplies do sell on trade me for cheap sometimes

yeah i know this is the best option, just biting the bullet and paying for quality usually is.been on trade me but havent seen anything yet.I am confident that the way i am thinking of going will do the job, just will be a bit more rugged is all.

31

I was having exactly the same problem and that tip from PaulUK sorted it for me. Probably gets a little too hot, so you will need a spring capable of pulling in and inch or two

32

quote ".First thing that needs to be made clear is that i am on a budget so i only want to do it on the cheap(or cheap as possible"quote

Hi Hunty!

I really get a better understanding of your topic from your last post. You want a no budget solution if there is one and reliable success for any unavoidable expense. I thought in this direction in my post above, where i suggested , that you put a slideable contact on one side of your bow. I guarantee, if you can adjust the length of the wirepart included in the electric circuit by sliding the contact, you will definitely arrive at a length (however short) which your 12V charger will get to glow. This should so far cost you nothing. If the glowing wirelength is to short, you then exactly know the ampereage needed with your wire, because if you need say a 35% longer wire, you need 35% more ampereage with the same 12 volts (or 35% more voltage with the same amperes). This is what muhleder already posted on simple proportionality. There is no use in changing voltage while you are using batterychargers or batteries. It´s the same effect on the wire, whether you use a 24V charger with 1 ampere or a 12V charger with 2 amperes. Unless you drive a lorry and need the 24V charger anyway, you better use what you have, and vice versa. On the very cheap side the slidecontact controll is enough to adjust the temperature. I know i repeat myself and others, but i hope to clear things up this way for those with just half a foot in the door concerning electrical stuff.

quote “BTW “the chemophysical backgroud on the collapse of polystyrenebubbles at contact with a glowing metalsurface or the glowing itself” sounds interesting, feel free to elabourate if you have the time” quote

I asked that, because I was puzzled by your firm wish to further clear up the matter in terms of theory at a point where i thought almost every practical question had been sufficiently sorted out by one poster or the other.

Of course some people have interest in backgrouds of backgrounds of backgrounds, and it´s nice if you have as well, but around here people would be most entitled to be bored to death with the matter, because you can´t surf like a hotwire through eps having the bubbles collapsing around you, almost without touching them in an atmosphere of gases, that where used foaming everything and within yourself feeling clouds of electrons propelled by invisible fieldforce to the horizon in the other end getting forced to dance wilder and wilder, around the real fat but agile ni crom guys who step in the way, and as the party gets hot leaping off the metalseesurface like flying fish but hoovering in midair suddenly free from the force at most…well…well…who wants to know that? But it´s not only rhetorical, and i´d hate it if it were.

doublecheers - d.