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Foam cutting help

Old 10-28-2002, 04:48 AM
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rahtware
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Default Foam cutting help

Just getting back into scratching and need to start cutting foam for a couple of my own designs. Misplaced my "bow" a few years back and can't find a source of wire to make a new one. My old one was made with nichrome wire, is that still the wire of choice? Any sources and information appreciated.
Old 10-29-2002, 01:30 AM
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Scott Smith
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Default Foam cutting help

I just cut my first set of cores using .020 SS Safety Wire from www.aircraftspruce.com ($8.80 for a 1 lb spool...should last a lifetime!)

I built this power supply:
http://www.nsrca.org/technical/tip_t...wer_supply.htm

and this table:
http://www.charlesriverrc.org/articl...gmancutter.htm

and got excellent results.
Old 10-29-2002, 02:23 PM
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rahtware
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Default Foam cutting help

Scott

Thanks for the tips. I downloaded the plans for the power-supply. The electronics supply house is on my list for when I visit the "big city" next week.
Old 10-29-2002, 06:07 PM
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Jaymom
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Default Foam cutting help

Scott ! What our chances of getting you to show us some pictures of your foam cutter, especially the way you set up the power supply.

Did you buy your parts from Radio Shack ?


I too am ready to build a foam cutter. My son started scratch building a Das Bipe Stik yesterday.

We're getting active again !
Old 10-29-2002, 06:08 PM
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Default Foam cutting help

Go to your local sporting goods store (Wal-mart or K-mart even) and get some steel fishing leader. Very cheap and comes in lots of sizes. I used to use the .020 size. Works great and is much cheaper than nichrome.
Old 10-29-2002, 10:08 PM
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Scott Smith
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Default Foam cutting help

Yes, I got all the parts exactly as listed in the instructions. The one thing I did different was etch the circuit board...very easy, just trace the runs with a Sharpie and etch with PCB Etchant.

I must admit, I put the triac in backwards the first time and it didn't work so well!

Here's the bottom half of my first cut (h. stab for Patriot 3D):
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Old 10-29-2002, 10:19 PM
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Scott Smith
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Default Foam cutting help

...and set up for the second cut. My formica templates are bolted to L brackets which in turn are screwed to the table. A lot of work but very repeatable. By attaching the templates this way, you can test the swing arm/wire travel very easily with the foam out of the way.
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Old 10-29-2002, 10:52 PM
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Jaymom
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Default Foam cutting help

Scott... looks like your well set up for foam cutting. I'm anxious to see how you have your table and rollers set up. What determines where you put the rollers and bar and where did you buy them? What did you use?
Old 10-29-2002, 11:16 PM
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Jaymom
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Default Foam cutting help

Scott, I didn't even notice the web address's you gave us up above. Just went there and have downloaded everything on them. This should be a fun project. Would still enjoy looking at pic's of your setup though. You can bet I'll be asking questions in the near future. LOL
Old 10-30-2002, 10:52 PM
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Scott Smith
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Default Foam cutting help

Here's some pics of my power supply. If you build one, I recommend:

1. Etch your circuit board
2. Install the 10 ohm resisters with ample space between the bottom of the resistor and the circuit board (these resistors do get hot!)
3. Install the triac correctly

This unit will supply a little over 4 amps at 27 volts to my 44" bow.

The potentiometer was at about 80% when I cut my 36" wing with the 44" bow.

Thanks to Tom W. for posting the project!
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Old 10-30-2002, 11:19 PM
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crashed2
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Default Nichrome Wire?

In my own quest to find this nichrome wire, I have found a place to get it in 100ft rolls for around $15.00 for .0201 size.

Go to,
www.pelicanwireexpress.com

see if they have what you are looking for.
Old 10-30-2002, 11:35 PM
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Ollie
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Default Foam cutting help

I don't know of any professional foam cutters that still use nicrome wire. Stainless steel is better in every way. It is not as brittle. It is freer of kinks and bends. It can be used with higher tension. It is less expensive and easier to find. It lasts longer under heavy usage. It has a smaller temperature coefficient of expansion so that it is easier to maintain wire tension as the wire heats.
Old 10-31-2002, 12:28 AM
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Default Foam cutting help

...and one last picture of the various jigs, templates, etc. The board, alumimun channels, window locks (on drop arm), rollers etc are all from Home Depot (about $40 total)

To figuring out where the inner line attached I used:
Length of drop arm * tip cord / root cord

For my wing, this was 40 X 7.6 / 18.5 or about 16.4 inches. Then a few test passes to get it exact (you can almost see the L/E & T/E marks on the templates that I used for this)

The blocks holding the C template have a pin that goes through an alignment hole on the cord line. I used these to properly set the height of the template before drilling the L bracket holes along the bottom.

I spent the last two months researching and making all this stuff and about 1 hour actually cutting cores! I am glad I decided to cut my own.
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Old 10-31-2002, 12:39 AM
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B Vial
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Default Foam cutting help

OK, I am building my own. I am assembling the CB into the box now and I have mounted all the other components.

The transformer has three leads on the output side. What did you do with your third (middle) lead? I am thinking of just capping it but not sure what to do with it.

If anyone else makes one. Layout your front panel to the high side with the switches. I am not sure if they changed switches since the original design (The original authors switches do look different), but I ran into some problems with room inside the project box. Thankfully I am able to cut some on my CB and create some more room as the backs of the switches left little room between them and the transformer for the CB panel.
Old 10-31-2002, 12:48 AM
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Scott Smith
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Default Foam cutting help

your correct...cut and cap the black wire. I installed a second 6 amp fuse on the low voltage side and used the removed wire on the fuse to circuit board connection. (Fuse was installed after I smoked the first triac....but we now know what caused that!)
Old 10-31-2002, 04:42 AM
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Default Foam cutting help

Scott, would you please describe the process you refer to when you say...

The one thing I did different was etch the circuit board...very easy, just trace the runs with a Sharpie and etch with PCB Etchant.


I understand the first part to mean cut into the copper along the lines indicated that separate the six sections. Is this correct? What do you mean by "etch with PCB Etchant" and what is it?

Sorry for being so inexperienced .
Old 10-31-2002, 04:56 AM
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B Vial
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Default Foam cutting help

I also did what he did. I used the diagram where the connections are all just in one block. I drew lines between these connections and solid 1/8" circles where the components go through the curcuit board. Makes it look like a real circuit board as you see in your radios unlike the blocking that is done in the instructions.

Radio shack sells a kit to etch a board. I bought it and it comes with two cuircuit boards, etching solution, pen to mark the lines on your boards, piece of green pad to clean the protective coating off before you begin, and a solution to clean the ink from the pen off when you are done etching.

Its a simple process that the instructions explains well that comes with the kit.

This was my first project and I completed it without problems. If my scanner was working I could post a pic of my lines I used... sorry, but you can figure it out with just a little effort.
Old 10-31-2002, 04:59 AM
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B Vial
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Default Foam cutting help

One thing I forgot to mention... Don't make your line/hole layout without having the parts to compare them to. The original design layout didn't match the size between holes for a few of the components for me. The triac is one that I remember being off between where the connections are on the component and the instruction guide for the curcuit board. If you do a block diagram board like the instructions say, all you have to do is move your holes. But if you do a line diagram board then you need to place your holes first and connect the lines as required secondly.
Old 10-31-2002, 01:41 PM
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Default Foam cutting help

Very nice setup.

I have a rather crude setup but an easy power source. It is an old Astro Flight ac/dc battery pack charger, left over from R/C Car days.

I have a variable transformer stashed somewhere but couldn't find it. So I tried this charger and it works great. the small things I usually cut with it require about 1 amp, using .014 ss fishing wire, very nice smooth cuts, limited only by my ability.

one of these chargers went on Ebay for 9.99 a couple of weeks ago.

(hope the photo shows up)
Old 10-31-2002, 01:46 PM
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Default Foam cutting help

Maybe now
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Old 10-31-2002, 02:15 PM
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Default Foam cutter template material!

I found a great source for aluminum template material. There are probably cheaper alternatives but this is a reliable source that is open late. I use aluminum kickplate from Lowes or Home Depot. This is the stuff you screw to a door to protect the bottom from scuffing. They have brass too but it costs twice as much. The aluminum cuts nice with a saber saw using a fine tooth metal blade. I saw close to the line and finish to the line with a 3" dia sanding disk mounted in my electric drill.
Rob
Old 10-31-2002, 05:05 PM
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Jaymom
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Default Foam cutting help

B Vial, thanks for all the tips. I saw that box while I was at Radio Shack and didn't think I was going to need it but I can now see where I will be going right back there and buying one. I spent 2 hours yesterday trying to find just one CB , any size. Bought the last one in Spokane as far as I can tell. I've put this project off too long now.
Old 10-31-2002, 05:34 PM
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rrandletn
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Default Foam cutting help

You can still get the wire from SIG.
Old 10-31-2002, 09:37 PM
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mwright
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Default foam cutting

I too have been experimenting with cutting cores.

What causes your cores to be lower in the middle (dipped out)? I think the wire is just lagging behind and dips out the middle. It is heat, tension, wire size or all of these? It think the heat is OK since any hotter and the cores want to melt to the shucks. I have the stainless wire very tight and the guage is .025" Maybe I'm pulling too fast? Does a pulley systems work that much better? Sorry, lots of questions..

Marcus
Old 10-31-2002, 10:25 PM
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Scott Smith
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Default Foam cutting help

The pulley system makes it possible to easily cut a taper by yourself…that’s about it. What is your wire attached to? It will stretch quite a bit when it gets hot.

I've got 18" lengths of 1/4 music wire that maintain the tension. Without the wire, my long bow measures 51". With the wire installed, it's 44". Except for some over-burn at the tip, the cut was straight.

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