Hi Guys,
I could not see this topic on how to make a foam cutter or what type are available in the market...... Take my words back... I was looking under wrong place, should have seen HOT WIRE.... We already have a few threads started here.. Ah well I am modifying this now that I have uploaded all below. So guys enjoy the read, if you think it is repetitive, write your comments, we will get it removed .....


Please can you all give us your images and ideas on foam cutters. DIY and market ones. I need to build one so am surfing the net for all info.

I will upload all the info I accumulate on the way.... Thanks for your input.

The first blog I have found....

"I built a hot wire foam cutter with an oak 1" x 2.5", two music wire arms and some fishing leader. Powered it with a battery charger set on manual 12V 2A.
Cut two templates out of 1/8" aluminum and bolted them to a base. Used some very light EPS foam and got 3 wings cut in 10 minutes.The three following links are to the pages I got most all of my information from.

Two of these pages describe very similar and simple hotwire bows for holding the wire tight. The basic design is simply a strong base (Piece of oak or other hard wood) and two 9" pieces of 1/4" dia. music wire (Landing gear material available at the hobby shop) that are flexed to hold the tension. Wrap your cutting wire (Nicrome, stainless, guitar string) between the two ends while they are flexed and there you have the basic cutting bow. To put heat to mine I simply attached the alligator clips from my car battery charger (one to each piece of music wire) and set it for 12V 2 amp. This worked for several different kinds of wire but not all wire. The links are far more explicit than I am being.

As for creating a template for the shape of the wing, down load Compufoil. The demo version lets you set the wing shape perameters and gives you a printable template to use for making the profile forms. You simply cut the templates out with scissors and attach to plywood, formica, aluminum etc... and cut it out. You can either pin the templates the either end of the foam block you want to cut or mount them on the ends of a base plate like I did. I am not being much more specific than last time since all this is well illustrated in the attached links. Foamflyer gives the exact specifications for the airfoil on the first view of the plane. You just have to figure out how they are entered into compufoil.

The light EPS foam (seems almost too light) is what Foamflyer was using. I took one of my new wings out and taped a makeshift fuselage to it and it flew OK just like that with no tail. Did a great loop and then fell to earth without damage. Crashed it severl times with no damage since it is so light.


http://webpages.charter.net/rcfu/ConstGuide/FoamWing.html

http://members.fortunecity.co.uk/slmohr/rcinterest2.htm

http://www.public.iastate.edu/~orman/air/cutter/hotwire.html

Read more: http://www.rcuniverse.com/forum/m_3511182/tm.htm#ixzz0niYWsn00



1. new train model transformers aren't the way to go; some old ones are okay

2. A good way to go is a 12V or 24V transformer from All Electronics.com on a dimmer. 12 volts is probably sufficient for up to a couple of feet. 24 is preferred for big stuff. (You need the same amps either way, but more volts for longer wires. You can finesse this a bit by using very thin wire, but people seem to prefer 16- or 18-gauge stainless steel. It's strong enough to crank pretty taut for striaght cuts.)

3. a lot of people prefer stainless steel to nichrome for hot wire cutters. You can get a roll of 16- or 18-gauge stainless wire from Cabela's for about $9. (And you get hundreds of feet of it! Give some away.)

4. regular guitar strings are pretty low resistance, so you'll need more amps from your power supply if you use them. You can get stainless guitar strings, but you can't beat the cost of the wire from Cabela's.

5. You can gang two RadioShack transformers (or other transformers) of the same make and model together to get twice the amps. (That's what I did, when I decided I wanted 4 amp capability to cut dense and/or strange foams.) But usually it's easier to buy one higher-amp transformer from allelectronics, and costs about the same. " Paul


Read more: http://www.rcuniverse.com/forum/m_4968914/tm.htm#ixzz0nj7E5IAL

Deepak

"I'm preparing to put one of my first fiberglass kits into production and wanted to try making the plug out of fiberglassed foam. I researched home built hotwire foam cutters on RCU but didn't find anything to my liking so I went www surfing and found THIS. Pretty much followed the directions except I added a 120V red LED as a power indicator and made the "wand" out of PVC (figures 1-4). Works excellent and the dimmer switch regulates the temperature of the hotwire. Check out the test cut (figure 5). "


Read more: http://www.rcuniverse.com/forum/m_4968914/tm.htm#ixzz0nixM7l4K

"First off, ditch the idea of using a train transformer. The older ones are okay (many yrs ago) but nowadays almost all of them are current limited in short circuit - which is essentially what we are doing when hot-wiring.

VA is indeed volts x amps. The thing to remember is that it's the current (amps) that heat the wire. You will need aqbout 1.5 amps for light white beadboard, and the temp/current goes up if you have to cut coloured (blue) foam. You need it a bit higher than *that* temp if you want to cut EPP.

So, we'd be pushing a transformer hard if it's rated for 2 amps. I strongly advise going double that, to a 4 amp capable transformer so that you don't let the magic smoke out.

In order to push through the current that we need, we need *pressure* - that's what voltage is - electromotive force. If you are strictly sticking to very short bows, you won't need much pressure - 12 volts will do you for about up to 2 feet in length. If you want to make longer cuts, you will need a 24V transformer. My long bow is about 4 1/2 ft, and I'm using a 24V/100VA transformer - call it rated for about 4 amps (a hair over, actually)

This is probably your best place to get a transformer for a reasonable price: http://www.allelectronics.com/cgi-bi..._Xformers.html

Don't worry about that "VCT" thing - it means volts center tapped. You won't be using the center tap. All you need then is a *good* dimmer switch or a ceiling fan speed controller on the input (120V side of the transformer). Leviton makes a dimmer rated for 600 Watts that you can snag at HD for about $10 or so.

I built my own power supply, but if I had to do it again, I'd go with the transformer and dimmer switch. It's about the easiest/cheapest way to do it."   Brad

PS - do NOT use a cheapo dimmer switch. It cannot handle the inductive load, and it will fry!


Go to your local computer store , ask for a used power supply , usually they will give you one for free , or very cheaply , works great , also good for charging batts.



This was a very good video on U Tube   
http://www.youtube.com/watch?v=03u1Hf7Dm5I&feature=related

i prepared the foam cutter exactly according to the specification mentioned above. but the wire is not getting heated up. also when i checked the potential it comes around 1V whereas the transformer is 24v/1amp. pls help me out!!

Quote from: kalupaika on September 24, 2010, 08:05:46 PM
i prepared the foam cutter exactly according to the specification mentioned above. but the wire is not getting heated up. also when i checked the potential it comes around 1V whereas the transformer is 24v/1amp. pls help me out!!

Hi K,
Some how the voltage is dropping down to 1 volt?

Have you read all the notes above ; Read more: http://www.rcuniverse.com/forum/m_4968914/tm.htm#ixzz0nixM7l4K

I think you need to try out a few tests... (be careful, you might burn your hands if they succeed so keep them protected / away from the nichrome while doing these tests)

Can I suggest;
Disconnect the transformer leads.

Please make sure you are using nichrome wire as the resistance on the wire makes it heat up in your cutting jig.
Also the wires out of the transformer might be too long hence creating a heat shield!!! A good option is to use 2 feet a good quality speaker wire connected to a car/ motorcyle 12v battery or 8x 1.5v dry cells to your nichrome wire and see how that fares.

Now if that works, reduce the length of your wire between transformer and bow and try... see if you can get 10 to 12 volts.
Good luck

Question..

Can the computer SMPS be used as a source - it has 12V and 5V supplies with lot of amps?

yes