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View Full Version : Foam Cutting Power Supply Questions - Non CNC



11bravo
04-28-2007, 04:21 AM
Sorry this isn't CNC related but hope you folks will take pity on me and still answer my questions.
I am a high power amateur rocketeer and need to use a foam cutter to build a nose cone for an 8", 1/2 scale Patriot.
I built a foam cutting power supply using the info at-
http://nsrca.org/technical/tip_tricks/foam_cutter/foam_cutting_power_supply.htm
The bow that I scrapped together is ≈24".
Using a fairly heavy SS leader wire for fishing for the cutting wire.
Tinkered around with it cutting pink rigid foam insulation.
Worked OK but when I'd set the selector switch to "Long" I'd blow fuses quickly.
Figured that would happen.
Last Saturday I was making a small, 4" dia x 9" long cone and got almost all the way through it quite well but then fuses started blowing when the power switch was turned on.
Tried 1-1/2 amp and 2 amp fuses and they still fry instantly.
Figure something inside is cooked and I'm not an electronics guy.
Anyway, question is, can I just run 110v AC through the power switch, to the transformer and to ground and run the 24v AC from the transformer to the pot and then the bow without all the other stuff?
Just take the extra out.
Also, the pot only gives me variable power through about 1/2 of it's knob turn.
Wired to one set of contacts I get no variation (very little anyway) from about 8 o'clock to 12, then from there to about 4 o'clock it ramps up.
Hook to the other set of contacts it is just backwards.
Anything I can put in to get a smooth ramp up through out the turn.

Thanks much,

Greg

vulcom1
04-28-2007, 01:36 PM
Greg,
To start with there are various designs on the net. With yours I have my doubts cutting with the 2 amp transformer. On my old reliable one that I have had for years I have a 24 volt 5 amp transformer in a box with a light dimmer control on the 110 volt input with a fuse. This way you are varying the input and not the output. I have had to replace it once so you may be able to find something better. With your heavy guage wire it would require also more power. I use .015" stainless control line wire for model aircraft and one reel is a lifetime supply for me.
There are more complicated setups and I have just finished one but have no testing on it yet. I made it for a cnc foamcutter that I am waiting for the components from Hobbycnc. I know they are in the mail, it is just the old problem we have between the post office and customs.
Let us know how you make out or if I can help.
John

11bravo
04-29-2007, 12:21 AM
John-
Not committed to the transformer that I have, but it is the one I have, you know.
I don't remember the specs on the cutting wire I have but want to say that it's 0.024" dia or something like that.
I decided to do this one as I thought that it looked pretty slick and would be pretty handy.
I still have to dig in and see if I can find what cooked.
Appreciate your help.

Greg

vulcom1
04-29-2007, 10:07 AM
Greg,
When you figure it out I would go to thinner wire as the thicker or longer it gets the more amps required. Not saying you can't cut it with the 2 amp but it also does not give you much reserve.
Have Fun.
John

11bravo
04-29-2007, 12:33 PM
Yeah, I know, but I also forgot to mention that one of the things I need to do is to modify the bow to only about 12" or so.
Less unwieldy and less juice required to run it.