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Old Aug 02, 2012, 12:44 PM
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vtdiy's Avatar
Southern Vermont
Joined Feb 2007
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It's definitely a learning curve to start with -- I remember destroying wings myself at first. method is as important as getting the heat right.

I finally found that a light weight bow with a 28" cutting capacity worked best for me. I clamped the bow, wire up on the bench, and set the wing blank down on it at about mid chord until it contacted the pattern, then drew the wing towards me allowing the weight of the panel to keep it against the wire. No pressure. Also minimal pressure in pulling it for the cut.

I also found that gluing a short piece of piano wire running in line with the centerline of the pattern onto each tip of the patterns gave a guide for the cutting wire straight out off of the pattern at the end of a cut. This was important to not getting the concave trailing edge syndrome or notched leading edge. Also I always made my patterns a little large for the actual chord of the wing to allow for trailing edge loss and some sanding of occasional ridges,

I always made patterns out of aluminum flashing cut with aircraft shears and smoothed with a fine file.

Anyway it does take practice, besides getting the heat right, and trying not to force or speed up the wire.

ps. I don't think the power supply you show is particularly good (based on user reviews) or necessary for cutting a good wing. I used a 6 amp 12 V auto battery charger and a Harbor Freight router speed controller. It's more a matter of prccatice and method that you work out for yourself. Don't be surprised if it takes a few wings to get there. A delicate touch is important.
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Old Sep 03, 2012, 10:40 AM
Went to mow a meadow
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Originally Posted by frank48 View Post
Put an LED dimmer on the output from the PSU. You can then vary the power from 0-8amps

http://www.ebay.co.uk/itm/1x-DC-12V-...item2a1dc13e58
My LED Dimmer arrived today - and it works a treat...!!

Using it with a 12v lead acid battery and 30 inches of 0.6mm mig welding wire

Frank
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Old Sep 03, 2012, 11:07 PM
So broke I can't pay attention
Naples FL USA
Joined Mar 2009
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I just found this thread, and it's very interesting. I had knee surgery recently, still not ready to go trudging around the flying field yet. So, to keep myself amused, I built a hot wire cutter, with the KISS method. After a little research and a trip to Radio Shack ect., here is what I came up with, a 12v 3 amp transformer around $10, a cheap (residential) dimmer switch $5 which I housed inside an old empty PC Speaker case (Free), a blue LED w/circut board removed from a plug in night light, $1 at the Dollar store. I first made a kind of cutting table, to cut thin sheets, using a shelving plank that was laying in my garage, then I put together a bow using a yard stick from home depot 98cents and two 12" lengths of 1/2"x1/2" wood trim, with 29lb test .011dia stainless fishing leader wire from my tackle box, all in all it cost me less than $20. My son brought home some scrap sheets of EPS from work, for me to practise on.
I then made a pair of patterns/templates out of 3/4mm aluminum sheet, (kind of a Clark-Y airfoil) and drilled tiny holes just big enough for t-pins to secure them to the foam. After a few trials to find the required heat and cutting speed, I managed to get a few nice wing cores.
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Old Sep 04, 2012, 06:47 AM
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vtdiy's Avatar
Southern Vermont
Joined Feb 2007
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Excellent, Frank48 and Cayminlast. Also, interesting use of negative patterns Caymin. Never seen that before.

I haven't tried my LED dimmer yet with a DC source, but will. Have built couple of supplies out of transformers and dimmer switches. The calculator gives me a wide range of materials to try -- I'm interested in formed cutters at this point.
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Old Sep 04, 2012, 08:54 AM
So broke I can't pay attention
Naples FL USA
Joined Mar 2009
489 Posts
Thanks Vtdiy, going by the results of my experiments and testing, a negative pattern is by far the best method I've found so far. There are many vids and other info about weighted pulley systems, gravity feed tilted tables, suspended bows, CNC and other expensive/complicated hot wire cutting systems/methods that can easily confuse and frustrate most of us. Trial and error with the most simple, safe and cost effective set-up is key for anyone interested in trying this. It's almost like some of the folks who want to get started in RC aviation, and they choose an expert level plane or heli as their first, instead of going for a small simple entry level 3ch high wing trainer. I'm very satisfied with my set-up, as it works very well for my needs at the moment.
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Old Sep 04, 2012, 09:26 AM
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vtdiy's Avatar
Southern Vermont
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The gravity pulled bow and tilted table is neat though for cutting thin sheets of foam from thick insulation. 2 mm foam is hard to come by and expensive. Great if you can make it yourself -- especially from scrap foam.

And I've seen some really simple versions of tilt tables and gravity feed for sheet cutting -- as I'm sure you can imagine yourself. Basically make a hill and slide the foam or the bow down it.

I think of all the packing materials than can be used for this -- I have an ARF that was packed in more foam than the plane itself contained. Odd shaped, but if converted into sheets, perfectly usable for building planes.
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Old Oct 31, 2012, 08:03 AM
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Originally Posted by gmwahl View Post
Ok Steve, add this to your figures.

.023 carbon steel solid welding wire

28.5" between contact points

Set to cut at 3/8" per second with no wire lag

Battery voltage @ 12.08 volts with 3300 mah 20c

Results: It uses 5.3 volts to the wire. Draws 3.7 amps. Gives me 19.61 watts for .68 watts per inch.

I'm really liking the carbon steel welding wire for what it's worth. It's only 5.50 at harbor freight for a two pound spool and comes in a variety of diameters from .023-.035. Heats fast and seems pretty strong so far after cutting 6 wing cores. Next I want to try some braided low diameter wire and see if it works too. It would be nice to know what options are available to people when the wire of choice is just not available at the moment. Very useful
Great set up idea!
I will use this idea, but will use my servo tester instead of the receiver and transmitter.
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Old Nov 12, 2012, 01:17 PM
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BelgiŽ, Vlaams Gewest, Temse
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@ VTDI

Is it possible to make a copy from the spreadsheet where I can change the metric values for the wire length?

Ben
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Old Nov 15, 2012, 11:56 PM
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vtdiy's Avatar
Southern Vermont
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Possible, yes. But to what purpose. Everything else is in the spreadsheet derived from inches (resistivity, wire diameter, etc.) from data submitted by users. I'd have to change all that. And also the inch length input would no longer work. So I'd have to maintain two spreadsheets.

Easier to just download the free Convert.exe program from Josh Madison. I use it all the time going the other way.

Actually, I mostly do metric to inch conversions in my head. I multiply by 4 and then move the decimal place over two notches to the right.

For instance, 100 mm (times 4) is 400, and moving the point over two notches gives me 4. Four inches is close enough to 100 mm.

So if you want a 800 mm bow, how big is that? 4 x 800 (and move the decimal) = 32 inches, right?

Plug that into the Hot Wire Calculator if you want an 800 mm bow, okay?

Works for parts of a mm, too.

How big is .5 mm dia wire in inches? Well .5 x 4 = 2, and then move the decimal two notches, and it's .02" (close enough for these purposes anyway).

See -- you can do it in your head.
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Old Jan 03, 2013, 12:00 PM
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vtdiy thank very much for this job!
"resistivity" field - what units really here? mOhms per feet, or i'm wrong?
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Old Jan 03, 2013, 12:27 PM
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Moscow, M.O.
Joined Oct 2009
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can i post here links to another hotwire threads?

over dozen of them in the depts of the forum, not too easy to find...

http://www.rcgroups.com/forums/showthread.php?t=1665260
http://www.rcgroups.com/forums/showthread.php?t=1469281
http://www.rcgroups.com/forums/showthread.php?t=1535920
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Old Feb 14, 2013, 02:14 AM
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Hi, I have an e-fuel power supply. It has a buuilt in voltage adjust knob. So can I just plug a cutter into the supply's outlet and control power by varying voltage? Most importantly, is it safe to do it this way? Thanks!
My grasp of all things electronic is tenuous at best so please excuse me if it seems to be a stupid question to you, however, better stupid online than standing in front of a burnt home or burnt to a crisp lying in the morgue
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Old Feb 14, 2013, 02:55 AM
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Staffs, UK
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Originally Posted by pile up View Post
Hi, I have an e-fuel power supply. It has a buuilt in voltage adjust knob. So can I just plug a cutter into the supply's outlet and control power by varying voltage? Most importantly, is it safe to do it this way? Thanks!
Not really a good idea since the voltage is only variable between 15V and 24V. If you use a wire size/length which needs less than 15V (and many do) you're in trouble.

If the power supply was FULLY variable, i.e. 0V-24V, it would be great. Or you could use that power supply but use a brushed ESC and servo tester to control the power.

Steve
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Old Feb 14, 2013, 08:53 PM
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Originally Posted by slipstick View Post
Not really a good idea since the voltage is only variable between 15V and 24V. If you use a wire size/length which needs less than 15V (and many do) you're in trouble.

If the power supply was FULLY variable, i.e. 0V-24V, it would be great. Or you could use that power supply but use a brushed ESC and servo tester to control the power.

Steve
Thanks steve. I will dig out my old novak rooster and try it. Surprised about using a servo tester though, did not think it will handle the power required.
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Old Feb 15, 2013, 03:26 AM
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Staffs, UK
Joined Nov 2003
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The servo tester just provides the control signal to drive the ESC. It's the ESC that handles all the power. But unless I'm missing something that's a Novak car ESC which can only handle 8.4V so connecting it to a 24V power supply isn't going to work too well either.

It's a minefield isn't it ?

Steve
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