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Help! Hot Wire Cutter basics , question and tips

#1
Hi
I plan on building a hot wire cutter , approximately 50 cm ( 1'8" ) long . I have a PC charger, volt range from 15 to 19.5 , with a DC power plug-connector. (My original plan is to put a wire on the inside of the connector , and wrap another wire on the outer side of the connector , then connect theese two wires via the hot wire. )
Is this plan good or I am going to electroBOOM something ?
What type and diameter of wire am I going to need for the hot wire ?
Where can I read more about hot wire cutters ?
Any tips ?

Thanks
 

dkj4linux

Well-known member
#2
I recently built a simple 2-axis hot-wire cutter from two "near stock" ERC TimSav minimalist CNC machines. I used 30AWG nichrome wire (~6.5 ohms/ft) and passed 1.5 - 2.0 amps through it to cut 2" construction foam at 1000 mm/min. Here it is in action in 2" styrofoam...


and in 2" construction foam


23" donuts... a little slower at 800 mm/min...


This machine slaves the two sides together, so no fancy tapers... simple straight-through cuts only. Does this help?

-- David
 
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#4
I read that the best wire is nichrome 26 gauge , but I could only find 30gauge wire for electric cigarettes. After what point the wire is too thin ?
 

dkj4linux

Well-known member
#6
Either will work. The smaller diameter nichrome wire will have higher resistance per foot (30AWG is ~6.7 ohms/ft vs 26AWG at ~2.7 ohms/ft) and heats to cutting temp with lower current. From the temperature chart on the Jacobs site... for the same temperature (i.e. 800*F) 30AWG needs only ~1.5 amps whereas 26AWG will require ~2.6 amps. It probably comes down to finding a suitable power supply.

Screenshot 2020-06-14 at 8.11.19 AM.png
 

dkj4linux

Well-known member
#8
It depends on the length of the wire you're heating... and the voltage and current capabilities of your power supply.

I really don't know what your planned hot-wire cutter is going to look like or what you're planning to cut with it (tapered wings, 2d shapes, etc) and there's quite a bit more to this stuff than simply asking what size wire to use and whether it will melt or not. I'm old and tired and not prepared to go too far down this rabbit hole... so, I'll simply describe what I've done and you can adapt/ignore from there. This web page covers this wire power stuff way better than I ever could so please refer to it. Hopefully it'll make sense to you.

I needed to cut 2" construction foam for a SIL project. A ~4" length of 30 AWG nichrome wire (I already had it on hand) will be plenty to handle that thickness.

20200614_102815.jpg

For powering the wire at up to 1.5-2 amps (from the chart, 800*F to 1200*F), I needed at least 5 volts across ~2.5 ohms (resistance of 4.5" of 30 AWG nichrome wire). That's pretty readily available with a "power brick"-type supply... I had 12Vdc @ 6amps in my stash. If I used a fixed 12 volts, however, I'd need to power nearly 12" of wire (12v/6.7ohms = 1.8 amps) to stay in the 1.5 - 2 amp range. But I didn't want to power that long a wire... so used my Charsoon AntiMatter LIPO battery charger (from my RC days), with its "foam cut" (constant current) mode, to vary the voltage to set/maintain 2 amps (I believe other similar LIPO chargers have a "foam cut" mode as well) through the wire. Very handy...

20200614_102941.jpg


Here, the wire is powered... and the power supply has adjusted to 6.33 volts to provide the 2 amps through the wire. [Remember the connections to the nichrome wire have to be long enough to allow the wire to be positioned over the entire range of CNC motion so there's added resistance in the circuit connections to be made up for...]

20200614_103105.jpg


And the wire is just faintly glowing red at 2 amps... and way more than required to cut foam...

20200614_103139.jpg


I started at 1.5 amps for the 2" styrofoam Tux I had cut out previously... but found that the construction foam (Foamular from HD) is more dense and upping the current to 2 amps allowed me to power through its 2" thickness at 800 - 1000 mm/min feedrate.

I genuinely hope this is helpful.

Good luck. -- David
 
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#9
It depends on the length of the wire you're heating... and the voltage and current capabilities of your power supply.

I really don't know what your planned hot-wire cutter is going to look like or what you're planning to cut with it (tapered wings, 2d shapes, etc) and there's quite a bit more to this stuff than simply asking what size wire to use and whether it will melt or not. I'm old and tired and not prepared to go too far down this rabbit hole... so, I'll simply describe what I've done and you can adapt/ignore from there. This web page covers this wire power stuff way better than I ever could so please refer to it. Hopefully it'll make sense to you.

I needed to cut 2" construction foam for a SIL project. A ~4" length of 30 AWG nichrome wire (I already had it on hand) will be plenty to handle that thickness.

View attachment 171920
For powering the wire at up to 1.5-2 amps (from the chart, 800*F to 1200*F), I needed at least 5 volts across ~2.5 ohms (resistance of 4.5" of 30 AWG nichrome wire). That's pretty readily available with a "power brick"-type supply... I had 12Vdc @ 6amps in my stash. If I used a fixed 12 volts, however, I'd need to power nearly 12" of wire (12v/6.7ohms = 1.8 amps) to stay in the 1.5 - 2 amp range. But I didn't want to power that long a wire... so used my Charsoon AntiMatter LIPO battery charger (from my RC days), with its "foam cut" (constant current) mode, to vary the voltage to set/maintain 2 amps (I believe other LIPO chargers have a "foam cut" mode as well) through the wire.

View attachment 171921

Here, the wire is powered... and the power supply has adjusted to 6.33 volts to provide the 2 amps through the wire. [Remember the connections to the nichrome wire have to be long enough to allow the wire to be positioned over the entire range of CNC motion so there's added resistance in the circuit connections to be made up for...]

View attachment 171922

And the wire is just faintly glowing red at 2 amps... and way more than required to cut foam...

View attachment 171923

I started at 1.5 amps for the 2" styrofoam Tux I had cut out previously... but found that the construction foam (Foamular from HD) is more dense and upping the current to 2 amps allowed me to power through its 2" thickness and 800 - 1000 mm/min feedrate.

I genuinely hope this is helpful.

Good luck. -- David
Thanks a lot for the help.
The Page about Power Supply Calculations is also very helpfull
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#14
I dont think electricity will pass through the bow , since it only passes between the aligator clips. I am not 100% sure though..
Oh no it definitely passes thru the bow. I had my hand on the wire and it never got hot. Noticed something glowing out of the corner I'd my wire and it was my springs. It was the easier path shot that's the way it went.