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STYROFOAM (SPECIFIC)

Old 12-01-2005, 12:24 PM
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hnesitd1
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Default STYROFOAM (SPECIFIC)

Gentlemen,

re: Foam Wing Cores

Are the (in Canada) 8 foot x 4 foot sheets of Pink Foam insulation commonly sold in hardware stores suitable for wing core fabrication (hot wire)? I'm really interested in constructing a power supply and trying this method out but the more I read about foam (types) the more confused I seem to get. Apart from electrocuting yerself, are there other hazards to be aware of? My idea is to use a surplus (DC) computer power supply with rheostat to adjust current/voltage. Thanks in advance.

GDJ
Old 12-01-2005, 07:58 PM
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Default RE: STYROFOAM (SPECIFIC)

Foam density is the answer. Depending on the intended use pink is acceptable for most four to six foot spans when balsa sheeted or glassed.
Old 12-01-2005, 08:19 PM
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Default RE: STYROFOAM (SPECIFIC)

I have built a plane from scratch out of foam (pink) is best as when cutting with hot wire there is less fumes. almost did it all indoors. (but not recommended) here is a link for cutting foam using hot wire.

http://www.utahflyers.org/FCCut.php

roltech
Old 12-01-2005, 10:23 PM
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Default RE: STYROFOAM (SPECIFIC)

Pink and blue expanded foams are 2 lbs/cu foot. The white beaded stuff is only 1 lb/cu ft. Blue and pink are better for vac bagging as the pressure can crush the white foam. But for sheeted structures white beaded stuff is best. But if you want to do unsheeted models then blue and pink are stonger and can be more easily reinforced with tapes and stuff.

The white beaded stuff sold as house insulation is not the best for wire cutting. A lot of years back some buddys and I shared a big batch of virgin white beaded foam and it cut BEAUTIFULLY! My early tries with the hardware store stuff had left me wondering if I was doing something wrong. The fresh stuff proved that I wasn't. The only problem was that by dealing with a commercial supplier we had to buy a rather large minimum. The cost was only $200 split about 5 ways but you had better have a rather large pickup to go get it. We filled the entire back of my Nissan with cap and had to tie 4 more sheets to the roof.
Old 12-01-2005, 11:27 PM
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Default RE: STYROFOAM (SPECIFIC)


ORIGINAL: BMatthews

Pink and blue expanded foams are 2 lbs/cu foot. The white beaded stuff is only 1 lb/cu ft. Blue and pink are better for vac bagging as the pressure can crush the white foam. But for sheeted structures white beaded stuff is best. But if you want to do unsheeted models then blue and pink are stonger and can be more easily reinforced with tapes and stuff.

The white beaded stuff sold as house insulation is not the best for wire cutting. A lot of years back some buddys and I shared a big batch of virgin white beaded foam and it cut BEAUTIFULLY! My early tries with the hardware store stuff had left me wondering if I was doing something wrong. The fresh stuff proved that I wasn't. The only problem was that by dealing with a commercial supplier we had to buy a rather large minimum. The cost was only $200 split about 5 ways but you had better have a rather large pickup to go get it. We filled the entire back of my Nissan with cap and had to tie 4 more sheets to the roof.

Your right about the white beaded stuff, I started to use the blue and went to pink after they were out of stock of blue, and found out that while wire cutting there were less fumes, also you can sand it with a dry all sander to take the most rough area and then to sand paper to finish, For one set of wings I did not sheet it but painted with urathane paint or if using other paint I use Zinsser B-I-N shellac base primer sealer ( a couple layer) before painting. All of the plane is made of foam exept the ailerons, stab, rudder. elevator are balsam.
Hindges are contac paper. the total wieght for 60" w/span fuse 46" = 5.5 lbs w/OS46AX motor. It's a low wing using different wings, flat bottom, semi sem. to full sem. wing and can cut some of the wing span to fly even faster /w combination of prop size etc.

roltech
Old 12-02-2005, 05:34 AM
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Default RE: STYROFOAM (SPECIFIC)

Some really well written answers............thanks ever so much.
Old 12-02-2005, 09:26 AM
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Default RE: STYROFOAM (SPECIFIC)

In for a penny, in for a pound, eh? What are folks using these days for power suppies? I have a schematic for a nifty power supply but before I begin I just know that some of the components are going to be difficult to acquire. This device delivers variable 20 vdc to a nichrome bow....very smart. If I could entice some JPEGS or GIFs on from someone I'd be grateful..............thanks in advance.

GDJ
Old 12-02-2005, 08:15 PM
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Default RE: STYROFOAM (SPECIFIC)


ORIGINAL: roltech


ORIGINAL: BMatthews

Pink and blue expanded foams are 2 lbs/cu foot. The white beaded stuff is only 1 lb/cu ft. Blue and pink are better for vac bagging as the pressure can crush the white foam. But for sheeted structures white beaded stuff is best. But if you want to do unsheeted models then blue and pink are stonger and can be more easily reinforced with tapes and stuff.

The white beaded stuff sold as house insulation is not the best for wire cutting. A lot of years back some buddys and I shared a big batch of virgin white beaded foam and it cut BEAUTIFULLY! My early tries with the hardware store stuff had left me wondering if I was doing something wrong. The fresh stuff proved that I wasn't. The only problem was that by dealing with a commercial supplier we had to buy a rather large minimum. The cost was only $200 split about 5 ways but you had better have a rather large pickup to go get it. We filled the entire back of my Nissan with cap and had to tie 4 more sheets to the roof.

Your right about the white beaded stuff, I started to use the blue and went to pink after they were out of stock of blue, and found out that while wire cutting there were less fumes, also you can sand it with a dry all sander to take the most rough area and then to sand paper to finish, For one set of wings I did not sheet it but painted with urethane paint or if using other paint I use Zinsser B-I-N shellac base primer sealer ( a couple layer) before painting. All of the plane is made of foam execpt the ailerons, stab, rudder. elevator are balsam.
Hinges are contact paper. the total wieght for 60" w/span fuse 46" = 5.5 lbs w/OS46AX motor. It's a low wing using different wings, flat bottom, semi sem. to full semi. wing and can cut some of the wing span to fly even faster /w combination of prop size etc.

roltech
Sorry for the miss spelled what (dry all) was suppose to be drywall sander looks like wire mesh.

roltech
Old 12-02-2005, 09:35 PM
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Default RE: STYROFOAM (SPECIFIC)


ORIGINAL: hnesitd1

In for a penny, in for a pound, eh? What are folks using these days for power suppies? I have a schematic for a nifty power supply but before I begin I just know that some of the components are going to be difficult to acquire. This device delivers variable 20 vdc to a nichrome bow....very smart. If I could entice some JPEGS or GIFs on from someone I'd be grateful..............thanks in advance.

GDJ
I have a Wing MFG. 48" foam bow that I use a Sears 10/50 amp battery charger to run. I normally use 10a to cut with, but at 12v, I can't cut much more than 42" without the wire cooling too much in the center and distorting. I have found that the wire will draw only what it needs, even when set on 50 amps. Keep in mind this is cutting blue and pink foam. I have no personal experience with cutting the white foam.
Old 12-03-2005, 07:20 AM
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Default RE: STYROFOAM (SPECIFIC)

Thanks for the gen. I know folks use all kinds of things.......even auto batteries. I suppose the key is to have the ability to adjust (volts/current) the cutting wire temperature accurately. I've looked at several commercial power supplies.............this one might fit the bill:

http://www.abra-electronics.com/cata...el_xp-603.html



GDJ
Old 12-04-2005, 02:35 PM
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Default RE: STYROFOAM (SPECIFIC)

I'm using a converted 300W PC power supply to drive a pulse width modulation circuit that I built. Since I fly smaller planes, I seldom cut more than 25" cores. I use 0.018" 302 stainless steel spring wire (music wire) -- it stretches less than nichrome and seems to be less brittle, plus it costs about $7.20 for 285'. The PWM circuit allows me to fine turn the temperature and since output is DC, there is no tingle.

andrew
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Old 12-04-2005, 04:00 PM
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hnesitd1
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Default RE: STYROFOAM (SPECIFIC)

Andrew..........slick design..........thanks for sharing. Is there any chance of you providing a schematic? In any case, thanks again.

GDJ
Old 12-04-2005, 06:26 PM
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Default RE: STYROFOAM (SPECIFIC)


ORIGINAL: hnesitd1

Is there any chance of you providing a schematic?
The design is a fairly common approach for controlling brushless fan speeds in computer cases-- I just modified some of the component values to suit my needs. RF on the schematic determines the 555 timer frequency as part of the RC network -- I'm running about 115 Hz with RF of 34K ohms. D1 is a common rectifier diode used to block voltage feedback from fan spindown -- because the MOSFETs are extremely static sensitive, they can be damaged by reverse voltage (and handling). I included it on the circuit just for safety -- be mindful of the polarity, it's reversed from what you normally see. I used a 1N4002. The MOSFET indicated is a IRF510 rated at about 6A. I substituted an IRF540 rated at 27A. Transistors are common components and the IC's are a 555 timer and the little 741 Op Amp. Actual electronic component cost is about $2.50. The more expensive parts are case, banana plugs and pot knob -- the rest came out of my junk box. The dial number mask was made with Power Point.
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Old 12-04-2005, 08:13 PM
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hnesitd1
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Default RE: STYROFOAM (SPECIFIC)

Andrew.......you went to considerable trouble to answer my question.........your explanation is clear and concise......thanks! BTW - your club has a great Web Page...........my compliments.
GDJ
Old 12-04-2005, 08:45 PM
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Default RE: STYROFOAM (SPECIFIC)

[sm=confused.gif]Andrew--Where do you get your stainless steel spring wire? I have used nichrome, braided control line, and safety wire with good results [sm=thumbup.gif]but haven't been able to find a good source of stainless steel wire.

TIA Bill
Old 12-04-2005, 09:37 PM
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Default RE: STYROFOAM (SPECIFIC)

I think he said music wire which is steel spring wire. but the lenght would be limited??

roltech
Old 12-05-2005, 12:14 AM
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Default RE: STYROFOAM (SPECIFIC)


ORIGINAL: RAMFlyer

[sm=confused.gif]Andrew--Where do you get your stainless steel spring wire?
Bill --

I buy from [link=http://www.mcmaster.com]McMaster-Carr[/link]. Search for part number 9495K62 in the main page search box. 285' for $7.20

McMaster is a major supplier of most hardware (we use them heavily for many items used in our robotics lab) -- their service is excellent and I strongly recommend them.

Typical examples of products and prices: 3MM socket head cap screws (prop screws for NORVEL) $7.24/100; 350' SS braided cable, .015 for C/L cable, $7.00; 10' spaghetti teflon tubing to use with CA glue, .90/10'


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