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Old Aug 29, 2006, 05:00 PM
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rcgroupie's Avatar
USA, CA, Los Angeles
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CNC cutter and special alloy Hot Wire - works straight from a 12V battery.

I've been in the process of designing / building a custom cnc foam cutter, it became necessary to build a hot wire bow.

I've been reading all the posts by people who have had trouble cutting foam - especially EPP - with a hot wire.
As a metallurgist, I developed a special alloy wire that has the perfect characteristics for cutting foam.
All you need is a 12V car battery, and about 4' of special wire.

So far I have the wire, the stepper motors, controller, lead screws, and misc bearings, and it is starting to go together.

I also have some big blocks of 1.9 EPP 4' X 3' by 4" or so.
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Old Aug 29, 2006, 06:55 PM
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More info please! resistance per foot, tensile strength, wire gauge/dia etc?
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Old Aug 29, 2006, 09:20 PM
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rcgroupie's Avatar
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Quote:
More info please! resistance per foot, tensile strength, wire gauge/dia etc?
Since the development cost me quite a bit, the details are proprietary. If someone really wants some, please reply or PM and I'll consider selling some for a couple bucks/foot.
1. Attach leads to wire
2. Attach 12V car battery
3. Cut foam.
Small variations in length are possible for your specific foam - just move the leads.
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Old Sep 01, 2006, 08:19 AM
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United States, WA, Yacolt
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hmm...

How quickly does it move through the foam?
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Old Sep 01, 2006, 08:39 AM
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Attaching to a car battery like that is dangerous. Too many amps possible. Bad results.
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Old Sep 01, 2006, 09:57 PM
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rcgroupie's Avatar
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James:
Quote:
Attaching to a car battery like that is dangerous. Too many amps possible. Bad results.
Apparently you are not familiar with elementary physics.
Saucer:
Quote:
How quickly does it move through the foam?
Slowly. Too hot and the foam 'melts away' from the wire, causing a loss of precision.
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Old Sep 02, 2006, 11:51 PM
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And what are the 'perfect characteristics' for cutting foam?

Have you managed to build a wire with a negative temp coefficent of resistance?
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Old Sep 03, 2006, 02:20 PM
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Niagara Falls/Toronto area
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All you need is a dimmer switch and a 120/24V transformer. Then you can use stainless steel wire (braided or solid). http://www.rcgroups.com/forums/showt...72#post6002347
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Old Sep 03, 2006, 02:58 PM
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I made my swing arm foam cutter eons ago. I cut maybe 6-8 cores a year. Unless your in a production environment I see no reason to go CNC.

The power source for the wire seems to be all over the place. I tried some of the suggested methods and had nothing but trouble with breaking wires and running either to hot or to cold.

So I made up a regulated current power supply. Nothing fancy I just use a series pass voltage regulator set up to regulate the current. A very old design. It runs off off 14V. For the wire I just use piano wire from my hobby dealer. Costs about .50 as I remember. Never had a wire break and the temp holds spot on.

KISS is the key.
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Old Sep 03, 2006, 03:25 PM
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Dusty: Do you have a schematic for that?

Brad
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Old Sep 03, 2006, 06:52 PM
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Australia, NSW, Newcastle
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Quote:
Originally Posted by moreil
And what are the 'perfect characteristics' for cutting foam?

Have you managed to build a wire with a negative temp coefficent of resistance?
Now there's a thought! I could use it with my cold fusion powered DC generator I keep hidden under the bed.

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Old Sep 03, 2006, 08:51 PM
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Quote:
Originally Posted by OzDragonFlyer
Now there's a thought! I could use it with my cold fusion powered DC generator I keep hidden under the bed.


Yes, I was also curious to know if it was zero diameter wire...

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Old Sep 03, 2006, 10:20 PM
Fortune favors the brave.
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Vancouver, Canada
Joined Jul 2006
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Quote:
Originally Posted by rcgroupie
Since the development cost me quite a bit, the details are proprietary. If someone really wants some, please reply or PM and I'll consider selling some for a couple bucks/foot.
1. Attach leads to wire
2. Attach 12V car battery
3. Cut foam.
Small variations in length are possible for your specific foam - just move the leads.
I tried to use this contraption and look what happened to me!
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Old Sep 05, 2006, 08:16 AM
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Quote:
Originally Posted by rcgroupie
James:Apparently you are not familiar with elementary physics.
Which elementary physics is that? The part about melted wire burning flesh or the part about shorted batteries spraying acid?

Maybe you meant elementary electric design, the part about fuses.

I don't need that stuff. You see, I can predict the future and I see a trip to the E-room in yours.
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Old Sep 05, 2006, 11:14 AM
pushing the envelope
rcgroupie's Avatar
USA, CA, Los Angeles
Joined Jun 2005
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Quote:
I can predict the future
You apparently can't even predict the past.
I've cut and flown foam with it. EPP. So the bumblebee can't fly. Better revise your theories to fit the facts.
Oh, and maybe someday your mommy will let you fly glow. Props + fingers = too dangerous. Shouldn't you be in school?
Quote:
The power source for the wire seems to be all over the place. I tried some of the suggested methods and had nothing but trouble with breaking wires and running either to hot or to cold.
So I made up a regulated current power supply. Nothing fancy I just use a series pass voltage regulator set up to regulate the current. A very old design. It runs off off 14V. For the wire I just use piano wire from my hobby dealer. Costs about .50 as I remember. Never had a wire break and the temp holds spot on.
This wire maintains a stable temperature from a standard battery.
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Last edited by rcgroupie; Sep 05, 2006 at 06:13 PM.
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