Model_Mann

lawnsplus where did you get the instructions on how to build/make your foam cutter, ive not found any sites that help me, if you could.... could you possibly in a breif summary tell all of us here at RCU how to make a HOT-WIRE-CUTTER????? please....[][]

pro27

Model Mann.......

Try the following link, this is basically the set-up I use for cutting foam.
Since the power pac talked about is hard to come by locally, I am using a 12v, 1amp auotmotive battery charger for the power supply. It works OK, but it too has a circuit breaker installed inside it. I have to cut quickly before it kicks in. I'm currently looking for a more suitable power supply.

http://www.vatsaas.org/rtv/construct...irecutter.aspx

pro27

I hear you about the cost.......
around here, a 2" thick, 4x8 sheet is like $20. A 3" sheet is $26. (now you know why new homes cost so much). I picked up a 1 1/2" 2x8 sheet for just over $6. It is the type that has the tongues on each side for use in basements and such. It gives you a usable width of 22" ( have to cut off the overhangs).

How many amps is the charger you use? What type and size of wire are you using?

lawnsplus

I have no idea what amps the old charger puts out. I have found that instead of making the two wires from the charger to the STAINLESS STEEL cutting wire permanent, just put two small alligator clips on the ends going to the cutting wire. Make a test cut when the wire gets hot. If the wire is not cutting fast enough then move one of the alligator clips in closer thus increasing the resistence, if wire is too hot then move the clips farther apart. I hope this makes sense. I tried using the floral wire from wal mart but it gets too hot and breaks. The ss wire that I use was just laying around the shop, I don't remember where it came from. I made my cutter 32" wide and it takes a lot of juice to get it to cut but on the other hand I can play with the clips until I get it to cut like I want too. I cut a whole shipment of buoys for our race lake in no time at all. They were about 12" balls and the wire cutter did the job quickly and very clean cut.

pro27

Thanks for the info.

I think my main problem with my set-up is the over-load circuit in my charger. It cuts just fine for a short time, but then it 'kicks out' and takes a while for it to reset.
I even tried an old car battery. It breaks 1/16" music wire in about 10 seconds. If I could find a variable current limiter, cheap, that would be the ultimate......

TERBObob

My Feedback: (21)

PRO ,
How about one of those old OHMITE ceramic resistors ( potentiometer ) that they sell on the BAY for around $5.00 ? Would that work ? They are the BIG ones , not an itty bitty ( polka dot bikini - oops ... sorry about that .... guess I got carried away .. )
Anyway , its pretty big ... around 6 or 7 inches across and they are round with a heavy ceramic covering the wire windings .
I know that they are good for varing the voltage awful good . Years ago , I used one to regulate voltage to one of my Halloween animatronics . ( till I was stupid and dropped it on our concrete sidewalk ..[&o] )
That way , you could use a car battery charger with that inline before the piano wire.

revelation

Hey everyone. Long time no post.... I have a few suggestions for a hot wire if anyones interested. I made mine with 5 pieces of small pine which was very cheap and used solid ( not stranded ) nickel/steel trace wire from a fishing store. You know, what u use so that toothy fish cant bite through the line and swim away to freedom. It works a treat! For the cutter, i got a length of pine about 600mm or so and sandwitched in the middle of two other longer pieces. I put 2 more lengths in the gap created at either end at right angles so a put a few 10mm bolts through to hold them on. So u can swivel the 2 end pieces. At the tips of the end pieces on one side i attached the wire and on the other side, a loop (important!) of sturdy nylon rope. then i just stuck an old paintbrush or stick through the loop and spun it around until the wire was nice and tight. To hold it, push the stick through a bit more and let it rest on the middle piece of wood so it cannot unwind. Hard to explain so hopefully this pic helps...

revelation

To Power it, a simple way to stop ur charger from over loading is to put a battery in line with it. This way (i know it doesn;t seem like it..) the charger is just charging the battery (which will never draw too much current) and the hotwire is draining the battery. (which is being constantly charged). same setup as your car really. I use a 12v gell cell and a car battery charger on my wire trace and it works great. Lawnsplus is right, if you want it to go quicker or slower mover the clips closer or further apart. I made my cutter wide enough to take the width of my boats just. If i need a wider one, hey it only cost me about 5bucks to make and about 10 minutes.

revelation

here.

lawnsplus

Mine looks something like that but on the top (not cutter) I used a large spring for 1/2 the length of the top attached spring to one end and piece of allthread to spring and piece of allthread to the other. The spring came from a hardware store and holds tension on wire if you leave the end pieces lose where they can swivel. When the wire gets hot the spring keeps it straight without much sag in the middle while cutting. Oh yeah, I put a wing nut on one end of allthread to adjust tension as needed.

pro27

Don't know about them. Are they a fixed resistance, or is it variable, like a pot?

The thing is, I don't know how much to drop the voltage. I know I need about 2-3v to make good cuts at a decent speed.

TERBObob

My Feedback: (21)

Heres a pic of what I mean . Yes , they are variable and can handle a LOT of watts. They come in different sizes and can be found on the BAY for around $5.00



You could just get one of the OHMITE variable transformers that range from 0 to 120 volts ( ac or DC )



The transformers are aprox $20.00 on the BAY . ( and they inlcude the rheostat - variable voltage thingy ... )

pro27

Thanks Terbo......I'll have to check it out.

clocker

I'm new and I'm late to this.. bad combo.. ehhe

However..
http://ca.geocities.com/itschaotic/david1.html
At the bottom of this link and on the following pages is a bit of documentation on a little engine I built. It's a low temperature differential Stirling engine. It runs quite nicely on the heat of my hand. I love the little thing..heh

One of the elements that needed to be made very accurately was the foam displacer disk. I used a kids toy train transformer and some nickel wire to cut slices very accurately. I'm sure the same will be applied well to this hobby.

I used a very flat board of course and tied the wire to screws so I could adjust the height in small increments. The transformer was a cheap fix and worked perfectly.

Hope this helps.

Cheers! Ian.

pro27

A model train transformer IS the IDEAL power supply for a wire cutter. The main problem is finding one that is workable.

All the units made in the past few years have circuit breakers or fused circuits built in so they shut down when overloaded. Well, when you use it for a foam cuter, you are shorting out the circuit and it shuts down.
The hard part is to find an older unit that does not have this feature. Unless the unit is new in the box or has a manual, there is usually no way to tell until you use it. Why pay for something if you burn it up right away. I''ve got 2 dead train transformers already that are junk.

LtDoc

Another thought.
Rather than cut foam, why not mold it? Build a hull as an example, make a mold, then pour the foam into it. Yeah, lot of work, but an option.
Or, since most foam is disolved/melted by petrolium products, use a paint brush and acetone to 'paint away' the foam.
Or, shape a hull out of foam, fibreglass it, then desolve the foam out of the fibreglass with acetone (like the EAA guys do). You're left with a fibreglass 'shell' the shape of the original foam 'scuplture'.
- 'Doc

It's one of those days when I either play on the computer, thinking up wierd ideas, or go cut the grass. You can see which I'd rather do...

pro27

These are some really good ideas.
However....for my building style, not for me. But maybe it will give someone else an idea to try.

Each would have its merits as well as short comings.
I personally USUALLY build in wood. I will dabble now and then with the foam. Not that it's hard to teach an old dog new tricks, but rather it's hard to change someone who is set in their ways I've been building with wood ( I guess you could call it 'old school') for over 30 years. I HAVE advanced to some of the techy materials over the years and use them to suppliment my habit. But for me, wood is the way I mostly go.

Foam is an excellent floatation material, and would recommend it for others as such. It is also a good structural material (being the right type is used). I have also used it for making forms for glassing as you mentioned for many things in the past.

My big holdback, for the most part is what I call a decent setup (for me) to cut the stuff. Something I feel comfortable with using. I've tried many things in the past, but none felt right or gave the results I wanted. I just keep looking.......

asmithnc

mark, have you ever tried a table or band saw?

pro27

I know of people that have, and with good success.

I don't own either one though, and the cost for me would not be worth it.

Both would work easily for straight cuts, and the band saw would have the ability to cut curves, though with limited ability to cut curved front rake sections. But it could be done in smaller sections that would be glued together.

I like hot wire cutters for the speed, neatness of cut, simplicity of use and design, and cost.

Therre are many ways out there to cut foam. I just prefer the hot wire. The setup I have works. I'm just looking for something better in practical use.

1BADHD

I uase the table saw to do most of the cutting. Then use a rasp to shape the rake and sand it smooth. Works great!

TERBObob

My Feedback: (21)

Although , I have not yet constructed a hull from foam only , I can tell you that a nice HOT ( heated over a propane flame I use for a melt pot for aluminum and lead ) , I can say , that a HOT knife does wonders for shaping and what-nots ... but you have to be careful not to go to hard with the knife ... it melts FAST .
Otherwise , I am like PRO in the sense that I perfer wood ..[8D] ( besides , I use my basement for my work area ( in addition to other spots - LOL ) , and not sure that the wife would appreciate the smell of melting foam .