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Old Nov 09, 2003, 06:40 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Cool
Finally! Hotwire cutter built and progress on the P-51!

I've been spending far too *much* time researching the "how-to" aspect of building and far too *little* time actually building! My JKA P-51 has kind of been just sitting there because of this, except for the progress I made early on.

The fuse has been sanded to a more pleasing shape than it comes with, and the wing halves have been joined. Putting the spars in the wing taught me that even when you don't think you've used anywhere *near* enough Probond, it's probably WAY too much!

I was happy with how well brushing a little water onto the wood spar worked out to "kick-off" the Probond. I know now that I should have used a small brush to "paint" a very thin layer in the spar channel, instead of squirting it into the channel directly from the bottle.

I've kept saying that I was going to build a hotwire cutter but I didn't get it done, even though I'd collected all the parts. (More data! Crank up the search engine and get MORE DATA!)

Well, enough of *that*!

Today, I found some wood buried deep in the garage, and got busy. I went with a simple "H" frame, because I liked the "self-tensioning" device. That's nothing more than a door chain spring, a small turnbuckle, and some picture-hanging wire, running across the top of the "H."

The cross-piece is screwed and glued to the upright on one end, and has a bolt, some washers, and a wing nut to fasten it on the other end, so the upright piece can pivot a bit.

The cutting wire across the bottom attaches to a screw eye in the bottom of each of the uprights, tied on with a "Haywire Twist," a fishing knot, that is conveniently shown on the package that the 44lb (20KG) stainless steel fishing leader came in. (Couple of 4 or 5 bucks for 30 feet of the stuff.)

All I have to do is adjust the turnbuckle to give the maximum length to the tensioning wire across the top of the "H" frame, tie on the wire to the screw eyes at the bottom of the frame, and then use the turnbuckle to "tune" the wire, so it's nice and taught. When the wire heats up and stretches a bit, the spring keeps it taught.

Since this was to be an "experiment," the cutting wire only has 12 inches of useful cutting span. For now, that will do it for me. Later, I'll make a larger one, as well as a shorter one, built into a "foam cutting scroll saw," to cut former and ribs. I'll also make a dedicated "sheet-splitter," to split fanfold blue foam into 2 or even 3 thin sheets, so I can play with the "built-up foam" building technique.

Picture, below.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 09, 2003, 06:42 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
For a power supply, I was thinking about ordering that kit from Aircraft Spruce & Specialty Company, but for now, I'm going to use this old battery charger I dug up from the "Black Hole of Calcutta," also known as "the garage."

It *is* ancient, but it still works. I tested the cutting rig on a piece of dense white foam, about two inches thick. It seems that on either the 6 or 12 volt setting, when I flip the switch to the 6 A. setting, it will heat the entire 12 inches of the wire to a good cutting temp.

On the 2 A. setting, at either 6 or 12 volts, I have to move the power clips closer together, maybe 6 inches apart, to be able to reach a cutting temperature. That should be just fine for the scroll saw idea.

Picture, below.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 09, 2003, 06:45 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
What do I need a foam cutter for while building the JKA P-51? I thought you'd *never* ask!

This model is being built *light*. No coroplast doublers, instead, I'll be covering the entire model with 3/4oz. fiberglass cloth and WBPA. The fuse will be split first into left and right halves (with the hotwire,) so it can be hollowed out. Then, it gets glued back together.

The fuse will get split again, this time to make a hatch, like Ken Manuel does on his FFX Park Fighters, at Seriously Fun Models. At this time, I'll also cut the foam canopy way, so I can use it to make a "plug," to try pulling a clear plastic one. I'm still debating between making a "pop bottle" plastic cowl, and making a foam & glass "sandwich" cowl. (Actually, I intend to try both, just to see how they work out.)

I will replace those short segments of power leads on the hotwire bow with a single pair from the charger to the cutting wire. Also, I'll either put an "off-on" foot switch in line, or maybe a heavy-duty toggle switch mounted right on the bow.

If the battery charger holds up, and if it will power at least a 30 inch cutter, I'll stick with it. If not, I'll get one of Aircraft Spruce & Specialty Company's power supply kits. They sell cutting bows up to 4 feet! Not *real* sure I'll ever need that kind of cutting ability!

Just wanted to let you know that I didn't give up building and flying, just to do research. Looking around like I do, I find a *lot* of great info and ideas. It's almost a separate hobby! But, I'm back to "building," so I'll be posting some pics soon, as I finally get that P-51 going and into the air.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 10, 2003, 11:01 AM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
I've seen this "automatic tension" method mentioned serveral places on the web, but here's a close-up in case the idea is new to you.

Remember, one of the upright parts of the "H" frame is fixed rigidly to the cross-piece. The other pivots on a bolt & wingnut.

A pair of screw eyes are set into the tops of the frame, so that they can be slightly opened towards the outside, allowing for the other parts to be attached. A pair of pliers will close them up again.

The turnbuckle and spring both came from the same isle, where screen door hardware is kept. The spring is one of those used to keep doors from opening too far if caught by the wind. It did have some hardware attached on both ends that I didn't need, so I cut it away with wire cutters.

The wire is a braided "picture hanging" thing. It knots easily, just like string.

I loosen the turnbuckle so the two uprights of the "H" frame are nearly vertical, maybe toeing in slightly at the cutting wire end. I then use a "Haywire twist" knot to attach the cutting wire to the screw eyes on the bottom of the "H" frame. Now, I only have to use the turnbuckle to tension the cutting wire, attach the power leads, and cut!

As the cutting wire heats up and stretches, the spring maintains the tension quite well.

It was mentioned in another "hotwire bow" thread, you could attach the cutting wire to a pair of flat head screws, instead of screw eyes, to allow the wire to be positioned *very* close to the work surface. This would be good for splitting FFF for sheeting wings and/or fuses.

Myself, I'd rather make a dedicated "foam splitter" on a smooth formacia table top. The spring tension method could be easily adapted.

If you search the forums, you'll find that with a little imagination, you can make table saws, lathes, scroll saws, etc, all with hot wire for foam construction.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 10, 2003, 06:11 PM
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willin's Avatar
In my Blu heaven! near Lincoln NE
Joined Mar 2003
2,000 Posts
Hey there ! before you go splitting the fuse into to hollow the halves, check out what someone else is doing to get the same results. BQuick seems to have a great idea.

Me like you seem to spend more time amassing information on our subject than in actual building time so I can relate. However I do think you need to take a quick peek on the first thread of the page to see what I mean. Then get right back to what you were doing. No slacking! Hee Hee ! I like that you have overcome your weakness... now if I can overcome my income problem I will do the same and get busy. My 2 cents willin

http://www.rcgroups.com/forums/showt...hreadid=167058
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Old Nov 11, 2003, 07:47 AM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Thanks, that was an interesting thread!

But, I think the shape of the P-51 is a bit too different to lend itself to the same technique.

Besides, I've seen some threads that had pictures of a number of different foam carving tools, all home made. I want to try some of them.

You would *not* beleive the number of bookmarks I have collected in my "Aviation" favorites folder! ( gread deal of those are to threads on the E Zone.)

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 12, 2003, 10:02 PM
GenesisCreation's Avatar
United States of America
Joined May 2003
287 Posts
Hey Mike I'm following your thread with great interest. Thanks for sharing what you have learned, your pics are great.
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Old Nov 13, 2003, 11:41 AM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Well, I only did a little "experimental" cutting today, with a small wire cup, fitted on a hand drill. (Really have to get a Dremel, one of these days.)

Didn't have time to take any pictures, as I'm working in between "near-death experiences." (Been grounded the past few days with bronchitis.) I will get some pics of this part posted, in the next couple of days.

What I've found is that *if* you have the foam securely held in place and keep a *good* strong grip on the drill, you can remove a lot of excess foam, with pretty good accuracy. I strongly suggest you play with a scrap piece, first.

I can see where most of the foam removal from the fuse should be done with the hot wire, primarily the area between the top of the wing and the canopy/top hatch area. Since this model will have a large top hatch cut, running from the nose to just aft of the canopy, all that area above the wing can come out in a single, neat piece. (See the FFX Park Fighters thread, and Cheif Winston's P-51.)

Where the wire cup will come in handy, while the fuse is split into left and right halves is, in the nose, between the nose and the area over the wing, and in the rear of the fuse behind the canopy area. I will be leaving a block of foam in place, just behind the wing, to mount the rudder and elevator servos.

This will be a good time to hollow out the air scoop under the wing, as well.

Since it doesn't appear that I'm going to succumb to the illness today, I have to stop here and go to work!

Getting back to building has been good therapy!

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 15, 2003, 12:17 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Oh NO! Was this *supposed* to happen?!?

Yep!

I thought it would be easier to hollow out parts of the fuse, such as the tail section, if I first split it into left and right halves. This was done with the hotwire cutter. I'll be using either a flat disc wire brush, or the cup wire brush. You can see in one half where I did a little playing around with it, just to get the "feel" of how it goes. I'd really *hate* to create any unwanted openings!

Part of the hollowing out will be done with the hotwire cutter, after the fuse halves have been re-joined (Probond.) The area above the wing will be done that way. But while the fuse is in this state, I can leave an "island" of solid foam to mount the rudder and elevator servos, just aft of the wing saddle.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Old Nov 15, 2003, 12:19 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
The picture below with better explain what I'm talking about.

The top section labled, "Hatch," will be cut off after the fuse has been re-joined and that upper section will get hollowed out with the wire brush, or a "bent-wire scoop cutter" on a soldering gun. The canopy will be left solid, so it can be cut off and used to pull a clear plastic one.

The section directly above the wing cut-out will be done after the fuse has been re-joined. A template will be attached top and bottom, a hole drilled down through the area in one corner will let me drop one end of the cutting wire through. Re-attach the cutting wire to the cutter and a nice, smooth rectangle can then be cut out of the fuse.

While still in the left and right halves condition, the area forward of the wing saddle will be carved out to make the battery tray and motor/gbx area in the nose. At the same time, I'll leave a solid foam island, to mount the rudder and elevator servos. This is also when I'll hollow out the tail area, behind the servo mount.

And in the event I *really* screw it up, I can always order another fuse from JKA and try it again!

I'll try to post more pics, tonight, when all of this has been done.

Mike S.
(aka "mad mike")
Spring Hill, FL

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I crash, therefore, I FLY!
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There is no one true way.
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Last edited by mad mike; Nov 15, 2003 at 12:22 PM.
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Old Nov 14, 2004, 02:05 PM
Registered User
frankyfly's Avatar
Italy
Joined Sep 2004
791 Posts
Hi Mike,

I'm just trying to build a P-51 3D foam fuse using a self-made foam cutter.
What happened to your foam project, any update?
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Old Nov 14, 2004, 03:34 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Back-burner-ed, not forgotten!

Got sidetracked building Scott's J3 Cub and getting ready to start his Park Racer. Also, began building cd rom motors. (Whole new hobby, that one.)

I got the fuse hollowed out and glued back together, made the cut for the top battery/electronis hatch, and the wings basically shaped to include the LE fairing.

Once I can call the pair of Cubs "done," I should be able to squeez the P-51 inbetween the Park Racer and yet another project.

I decided against the Endoplasma power train in favor of a double-stator brushless motor. The Endo is being saved back for a larger scale warbird, later on.

As usual, I'm doing too many things at once to actually finish a single project! But eventually, each and every one *will* be completed!

As soon as I do manage to get a little more done on the P-51, pics will be posted.

Mike S.
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Old Nov 15, 2004, 11:48 AM
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frankyfly's Avatar
Italy
Joined Sep 2004
791 Posts
OK Mike, I'll be waiting for it !
See your pictures soon.
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