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Old Oct 03, 2006, 08:37 PM
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DIY foam cutter

I made this several years ago for cutting wings. It uses a swing arm with a Watts link for cutting tapers. Set up is fool proof, just set the link to match the taper and cut.

I use .02 common piano wire. Haven't changed out the wire since it was built. To prevent wire burn out I designed a current regulated power supply using a common 5 volt voltage regulator chip.

Probably over kill for a lot of folks but I enjoy designing and building stuff like this. Cores are a lot of fun to cut with this machine. I use Compufoil for the templates.
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Old Oct 04, 2006, 05:59 AM
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About 6 months ago I posted a request for info on just such a machine on the Hand Launch Forum after struggling with the drop bar cutter. I found a couple of examples of similar machines online. I never got much of a response. Your setup looks really nice, and buildable. I've since ironed out the bugs with the drop bar, but I'd like to see more info/pics on your machine.

Mark
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Old Oct 05, 2006, 12:34 PM
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Mark , here are some pics of my swing arm foam cutter. I hope you can figure out whats going on here. If not PM me. It's mounted on a cheap card table. I have a 2400 sq ft hobby shop so room is not a problem for me.

The Power supply's regulator can be seen on the left of the Transformer box. I'm running about 14V DC. Transformers were cheap when I bought this from All Electronics. They are expensive now due to copper costs. I have built some for friends with power supplies from computers.

One end of the arm has adjustable weights to counter balance the arm. It swivels up/down and left/right and is mounted on strong bearings.

The bow also swivels in two directions on small bearings. To adjust the wing sweep I move the small 1x1" bar extending out from the center of the bows swivel. The Watts link holds the bow parallel to the wing's front edge and then slowly moves out to the correct sweep angle to finish the cut. Of course if it's set for a straight wing the cut is kept parallel to the wing edges.
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Old Oct 10, 2006, 03:02 PM
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hey dusty

thats what I looking for. foam cutter with a normal piano wire! I got one paied but it works only for short wirers up to 20cm it uses 2.1 Volt and 9 Amps. Works with 0.5 or 0.1 mm Piano wires.
I think it is nice working without special resistant wire.

I want built a bigger "saw" now that should work from 60 to 100 or better max. 150 cm

but my electronic skill is not so well. Can you tell about your transformer? How much Power, Volt, Amps do you need? What I use to regulate it? and how to set that I get not a short? Have you a built plane for the circuit? ...
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Old Oct 10, 2006, 07:33 PM
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Ueliisa: Start reading at post #20 in this thread: http://www.rcgroups.com/forums/showt...72#post6002347
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Old Oct 10, 2006, 10:32 PM
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Quote:
Originally Posted by dusty IV
Mark , here are some pics of my swing arm foam cutter.
Hmmm, very interesting cutting mechanism you have there. I had to dig through my archives to look at the cutter mechanism I cobbled together in the pre cnc days. It is a simple swing bow with variable radius. I was only cutting tapered panels in those days but I had aspirations for a universal geometry mechanism like yours. Just... never... got around to it!

Im still trying to figure out the Watts Link geometry though from your pics. Do you set it up by trial & error to intersect the TE & LE planform, or do you have graduation marks corresponding to various taper ratio's on the front protruding bar to dial it in directly? Do you have any web links or similar references to see how the Watts mechanism geometry works?
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Old Oct 11, 2006, 05:32 AM
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OK I read the many threads and external links. and I have to Power Supplies both supports 20A by 13,8 or 12 Volts. I hope thats should be enough. I can now convert the PC one or use the ripmax direct.

Now I need some help to set up a controlled secure circuit for the saw for piano wire. (I look also for a Powersaving way with less of heating the air) I tell my idea:

the original use 2.1V 9A (0.23 Ohm, 18Watt) for about 20cm to heat a 0.5/1mm (diameter) Wire. So I can change the diameter, Amps and/or Volts. 9 Apms are enouch to heat the wire - I think i should not go up here.

Perhaps I can use 3 times more Volts because i go from 20 to 60cm first - around 6 Volts.

- I half the V with 2 resistors and set the hole Ohms to limit about 9A.
to get 6.9V by 9A: 2 resistors with about 0.76 Ohm for 62 Watt. The second must be splitted to a parallel for together 0.76 Ohm one side the wire and on the other to split voltage to 6.9 Volt. also about 1.53 Ohm.

- I use the full 13.8V and use a resistor to limit 9A. On the first view it looks more nice to me.
for 13.8V and 9A I need a 1.53 Ohm resistor for 124

Thats my understand of electric circuits. Is it possible?
Or should I use only a dimmer on the 13.8 Volt DC side? Is ther some to look about?

- My first try to buit is set 55 Watt carlamps in parallel as many as the wire goes hot. The wire in serie with lamps. So I got 5 steps: 55, 110, 165, 220 and 275 Watt (13.8Vx20A=276Watt) With a smaller lamp I could make steps between. But I think thats more a quick and dirty DIY. Only one advanced a big part of the lost Power goes as light not as heat.
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Old Oct 11, 2006, 05:39 AM
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Quote:
Originally Posted by ptxman
Im still trying to figure out the Watts Link geometry though from your pics. Do you set it up by trial & error to intersect the TE & LE planform, or do you have graduation marks corresponding to various taper ratio's on the front protruding bar to dial it in directly? Do you have any web links or similar references to see how the Watts mechanism geometry works?
http://aeropic.free.fr/pages/modelisme/decoupe/
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Old Oct 11, 2006, 05:58 AM
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Quote:
Originally Posted by ueliisa
OK I read the many threads and external links. and I have to Power Supplies both supports 20A by 13,8 or 12 Volts. I hope thats should be enough. I can now convert the PC one or use the ripmax direct.

Now I need some help to set up a controlled secure circuit for the saw for piano wire. (I look also for a Powersaving way with less of heating the air) I tell my idea:
The way to save power is to heat less wire . It is the amps (current) that create the heat. The voltage creates the pressure needed to force the electrons through the wire - the longer the wire, the more volts you need to keep the current constant. The bigger (fatter) the wire is, the more amps you need. You are on the right track here.
Quote:
Originally Posted by ueliisa
the original use 2.1V 9A (0.23 Ohm, 18Watt) for about 20cm to heat a 0.5/1mm (diameter) Wire. So I can change the diameter, Amps and/or Volts. 9 Apms are enouch to heat the wire - I think i should not go up here.

Perhaps I can use 3 times more Volts because i go from 20 to 60cm first - around 6 Volts.

- I half the V with 2 resistors and set the hole Ohms to limit about 9A.
to get 6.9V by 9A: 2 resistors with about 0.76 Ohm for 62 Watt. The second must be splitted to a parallel for together 0.76 Ohm one side the wire and on the other to split voltage to 6.9 Volt. also about 1.53 Ohm.

- I use the full 13.8V and use a resistor to limit 9A. On the first view it looks more nice to me.
for 13.8V and 9A I need a 1.53 Ohm resistor for 124

Thats my understand of electric circuits. Is it possible?
Or should I use only a dimmer on the 13.8 Volt DC side? Is ther some to look about?
You understand well Have you ever seen the size of a 62W resistor? Or the price of one ? And I shudder to think of the size and price for 125W. The light bulbs may be quick and dirty, but they are also cheap.

You can't use a dimmer for DC either - you would need a big rheostat (again, it would need to be huge to dissipate the excesss power), or else a chopper circuit to control the power (which can be done - but not easily or cheaply. There are circuits available out there, but the price and complexity is more than the cheap and easy way. Why do things the hard way?

We use a 24V transformer because that voltage lets us use a wire that is fairly thin, yet not so thin that it breaks easily. 24V is also safe for complete idiots to use without zapping themselves I have danced the "funky monkey" too many times professionally to advise amateurs to play with high voltage

PLease go back and look again at the 24V transformer and dimmer switch easy circuit. This works well, is easy to put together, and is about the cheapest way to go.

Quote:
Originally Posted by ueliisa
- My first try to buit is set 55 Watt carlamps in parallel as many as the wire goes hot. The wire in serie with lamps. So I got 5 steps: 55, 110, 165, 220 and 275 Watt (13.8Vx20A=276Watt) With a smaller lamp I could make steps between. But I think thats more a quick and dirty DIY. Only one advanced a big part of the lost Power goes as light not as heat.
Trying to save power with a foam cutter isn't the best way to go. It doesn't draw much, and it's not on for very long. If you want to save power in your home, insulation and fluorescent light bulbs will have a much higher pay-back.

Brad
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Old Oct 11, 2006, 06:25 AM
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Do you mean the picture in:
Quote:
Originally Posted by arx_n_sparx
Whats the big differnce beetween the circuits in the both pictures?
How much is the power range of yours?
To can use it up to 10A? Have I only set the fuse to more than 10A?
And for the power on lamp i can use a low Watt 24V lamp? or some spezial needed?
In the second circuit can I put in also a power on lamp like the first use it?
If I order a dimmer what need I to know? Watts, VA, kind of built?

Thanks
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Old Oct 11, 2006, 08:53 AM
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Hi Dusty IV,
Your wing cutter is very interesting. It sure looks like it makes cutting cores a simple matter. I am confused about one thing though.
I dont see what makes the hot wire travel through the foam. Is there some kind of
weight that pulls it throgh or is it done with hand pressure.

good job

TIM
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Old Oct 11, 2006, 06:23 PM
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Quote:
Originally Posted by ueliisa
Do you mean the picture in:

Whats the big differnce beetween the circuits in the both pictures?
How much is the power range of yours?
To can use it up to 10A? Have I only set the fuse to more than 10A?
And for the power on lamp i can use a low Watt 24V lamp? or some spezial needed?
In the second circuit can I put in also a power on lamp like the first use it?
If I order a dimmer what need I to know? Watts, VA, kind of built?

Thanks
The circuit is the same - the one on the left has an on/off switch and a power on light added.

This circuit should not need to draw more than a couple of amps on the output of the transformer. 2A on the input side is actually a bit of overkill, but it's better than rating the fuse a bit too close to actual input power and having to replace nuisance blown fuses.

The power on light is whatever your mains voltage is. I realize that english is not your first language, and I am assuming you are in europe. I have been known to assume wrongly though. In that case you would want a pilot light rated for 220V.

The dimmer switch is rated for 600 watts at 120 volts. You would need to find one rated for 220 volts. Make sure it will handle at least 500 watts. The alternative is to use a speed controller for ceiling fans - these can handle the inductive load. A cheap dimmer switch will probably fry itself.

You should check with a friend near you who is familiar with electrical stuff to help you on this.

Brad
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Old Oct 12, 2006, 03:29 AM
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Hi Brad

you are right I am swiss-german and since 2 month in Helsiki Finland. Next week I go for Holiday to Switzerland and then I go to my electronic store with a good consulting/guidance.

I will get all the stuff I need to built this 24V transformer and the "DIY Test Fixture to Measure Motor Resistance (Rm)" http://www.rcgroups.com/forums/showthread.php?t=580151

here in finland I found no store and no people that helps me yet ... - perhaps a finish read it and contact me 8-))

Sorry I mixt the 110V(for me 220V) with the 24V side - now it is mostly clear!
The right one has a green wire on the dimmer you connect it to the with (fat blade) or the black (skinny blade) one?

If you use a 2A at 110V(240V) so I get for 24V the max output of 9A(20A) without burn the fuse. - So the transformer must also support some more Amps on the secondary side:
- 110V by 2A fuse needs support up to 15 to 20A on the secondary 24V side
- 220V by 2A fuse needs support up to 25 to 30A
- 220V by 1A fuse needs support up to 15 to 20A
Thats right?
How are information data for transformers for the primary or the secondary side?

How controlls the dimmer and the speed controller for ceiling fans? Volt or Amps?
If Volts I could use the circuit also as power supply to other things ...

looking in a online store I saw different dimmers: "segement phase", "angel phase" and others. Is it important witch one I use?

I it possible to built the circuit on a "pc board" (how is the name of that) or have I to make free "flying" wires in a box? What I need to know about the pc-board for 240V and many Amps (use inside 2.5mm multistrut wire or 1mm single wire)

I hope with all this information I am ready to ask my shop about the stuff.
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Old Oct 12, 2006, 02:11 PM
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DIY StyroSaw CarLamp TestFixing

hi did some tests (see also the picture) this afternoon here the results:
Equipment:
- Peak Pro PowerSupply with 13.8 V and max. 20 A
- eMeter with the 100A Shunt for Volt, Amps, Watt
- 4 CarBulb Philips 12V/55W
- 0.5 and 1.0 mm common steel Wire length 1m from StyroCut 3D
- 0.3 and 0.33mm guitar chord length 1m

eMeter shows using 1 bulb 4.6 A, 2 bulb parallel 9.3 A, 3 bulb 13.8A, 4 buld only 15.2 A here also the buld reduce its brightness.

the 1mm wire (about 0.13 Ohm) needs 12,2 A (using 3 bulbs) to cut styro and depron nice.
the 0.5mm (about 1.72 Ohm) cuts with 4.3A (2 bulbs)

the 0.33mm guitar chords (about 3 Ohm) cuts slowly cutting after a long heating time by 4.6 A at 13.8 V (no bulb)
the 0.3mm guitar chords (about 5.57 Ohm) gives me at 13.88 V (no bulb!) only 2.49 A - it was not cutting

the conclusion:
- 12 V is posibble but 24V transformer for nice workin
. --> for small bows about 20 to 60 cm 12V is ok
- wire should be under 0.5 mm but also the resistance is important!
- for 1m I need about 3 to 5 A (13.8V)
- for small bows about 20 to 60 cm 12V is ok

Please do not copy the test fixing on the foto. It could be dangerous!
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Old Oct 12, 2006, 08:44 PM
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Quote:
Originally Posted by ptxman
Hmmm, very interesting cutting mechanism you have there. I had to dig through my archives to look at the cutter mechanism I cobbled together in the pre cnc days. It is a simple swing bow with variable radius. I was only cutting tapered panels in those days but I had aspirations for a universal geometry mechanism like yours. Just... never... got around to it!

I'm still trying to figure out the Watts Link geometry though from your pics. Do you set it up by trial & error to intersect the TE & LE planform, or do you have graduation marks corresponding to various taper ratio's on the front protruding bar to dial it in directly? Do you have any web links or similar references to see how the Watts mechanism geometry works?
To tell the truth I'm not sure this set up is a true Watts link. It's been a long, long time since 101A mechanics/physics classes. Type in watt's link on Wkipedia.com for an automotive type axle locater. All it is is two parallel rods side by side with a sliding adjustment at one end. This throws the rods out of parallel and causes one end of the link to move further the the other end. This results in a taper when cutting foam.

Graduation marks could be used but it's much easier to simply place the wire on top of the tapers edge and side the adjustment bar until the wire lines up. Much easier to do then describe. Make up a model with junk dowel sticks and play around to see what's going on.
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