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Author: Subject: Unconventional Shaped Charges
Deceitful_Frank
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[*] posted on 15-4-2006 at 09:04


...update:

I have now completed the conicle shaped charge, glued the cone and drilled the hole for the blasting cap. As you can see from the pic, it is supported on three plastic legs and has a standoff of 1.5 cone diameters or 1.5 inches.

It is the second time I've been at this stage due to constant difficulties making it waterproof. I had to scrap the last cone and form a new one which is better sealed with epoxy. It is also slightly flatter with an internal apex angle of 80 degrees compared with the previous 60. Maybe slightly less efficient but it does give vital extra millimetres internally to address the headheight problem... we will see

I've just now to make the cap. It will be 0.5 grams of fresh HMTD in a strong plastic tube measuring 7mm X 23mm internally. This will be weighted down with Blu-Tak so that 5-10mm of the cap protrudes into the hole at the top of the charge when COMPLETELY full of EGDN. This may cause a ml of overspill but that shouldnt be a problem.

The fuse will be of my own 7-8 second homemade variety and a tin of baked beans 20cm from the charge will serve as a blast witness plate... and to catch any shrapnel!

I started my HMTD synth last night so hopefully just a few more days to blastoff!


[Edited on 15-4-2006 by Deceitful_Frank]

SC2 copy.jpg - 63kB
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[*] posted on 17-4-2006 at 03:13


Finally I have found a way to produce perfectly symmetric liners in almost every thinkable shape and size. It does however require a metal spinning or metal turning lathe and a little practise. A lot of work for a liner, but once you have al the equipment, its about 5 minutes to make the liner itself...

I came to the idea when I saw a television program in which coppervases were made by a technique called "metal spinning" A circular metal disc is spun at about 1000 rpm and forced around a form or mandrel with a shaping tool.

Pictures say more than a thousand words:

http://www.coe.ufrj.br/~acmq/spinning/

A friend of mine had a metal turning lathe so I decided to give it a try. The mandrel was made very quickly. I bought me some playdoh, put in one of my remaining candle lightbulbs to get a form. Then I took about 15 cm of scrap 15 mm hollow steel tubing and drilled some holes in it. This was hung in the playdoh form, centered and free from the walls. The form was then filled with polyester and, after hardening, sanded down in the lathe until completely centered.

This was the result:


here an overview of what is needed:


The copper sheet I used was 0,5mm thick, but even 1 mm sheet is still workable. Annealing is very important with copper as it hardens very quickly. It is nothing more than heating the copper until redhot with a blowtorch and dumping in water. This restores the neat arrangement of the metal atoms in their raster and makes the metal very soft and pliable. As copper hardens very quickly again it was nessecary to anneal about 4 times more during spinning.

The result: (base of the cones is not yet equalized)



The cone on the right was one of the first attempts and some circular grooves, due to too much pressure aplied, can still be seen. The cone on the left has a nice mirror sheen and was made after maybe 10 failed attempts. The technique is realy surprisingly simple and doable in 5-10 minutes for every liner! Althought the guy with the website I gave above says it is a difficult technique to master, it only took me about ten attempts. I still have to put the cones to the test, but I don't think a more symmetric liner can be produced this easily.

I do not think many people will actually try it, but if you happen to have or know anyone with a turning or spinning lathe, give it a try!

[Edited on 17-4-2006 by nitro-genes]
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[*] posted on 17-4-2006 at 03:16


And for those who want to try, this is a good tutorial:

Attachment: spinning.pdf (212kB)
This file has been downloaded 1465 times

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[*] posted on 17-4-2006 at 03:53


Dang, this is interesting. I don't have a lathe, but it should be possible to make something similar with a drill pess and a base with a ball bearing.
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[*] posted on 17-4-2006 at 08:02


It seems that some method of "grip" needs to be imposed on the sheet before the working tool is pressed into the copper. The tutorial was excellent but did not cover that (mandril grip) and as I look at your setup I understand the contra mandril being used....is pressure the method of adhestion and grip from the mandril itself? Is that why you used the mandril material you did? - GREAT idea!

----If this is so the idea of using a mandril of steel (ball-bearing) or other lower-friction material may be a frustrating proceedure----

[Edited on 17-4-2006 by quicksilver]




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[*] posted on 17-4-2006 at 09:44


Ah yes, spinning, fun stuff.

Drill presses can't handle any sideways forces. You really need a metal-cutting or metal-spinning lathe to do it.

Fortunately, there are several machine shops in any moderately sized city. You may even know someone with a lathe and not know it.

Tim




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[*] posted on 17-4-2006 at 10:02


The drill press method could work I think for not too large spinnings it would have enough power I guess. 12AX7 might have a point though about the sideway forces. Though a lot of force is directed downwards and the amount of force necessary doesn't appear to be that great at all. (I was quite surprised by this) The annealing makes the copper soft enough to be hand bent and twisted even when 1 mm thick sheet is used!
You would only need to make an improvised toolrest. Be sure though to stay below 1000 rpm, or strange things might happen...;)

The mandrel and contra mandrel are screwed together with the sheet metal in between. So, the grip is indeed only provided by the contact surface of the mandrel and contra mandrel on the sheet metal. Basically the sheet metal is clamped very tight between mandrel and contra mandrel. This provides enough grip to apply quite some pressure with the working tool.
Only be sure that the contra mandrel has no sharp edges where it contacts the sheet metal. When too much pressure is applied, this is where the sheet metal ruptures or wrinkles. (my first 5 trials :))

This is the total picture, the contramandrel is actually nothing more than an adapter between spinning centerpiece and the mandrel itself:


The material of which the mandrel is made does not really matter, I chose this material because it is fast and cheap and I had no idea if it would work at all. In fact a lot of materials can be used, ranging from tropical wood to stainless steel. Steel would make a far better mandrel. Because even after, say 10.000 spins, the steel mandrel would still have exactly the same shape, while wood and plastic mandrels are slowly sanded down by the pressure applied on it with the working tool and thus loose shape.

The technique is a sort of "rowing sweeps". a nice indication is this movie clip. (This guy makes it look real easy btw, I think he has done this more than once ;))

http://www.franjometal.com/metal-spinning/spinning-videos.ht...

[Edited on 17-4-2006 by nitro-genes]
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[*] posted on 17-4-2006 at 12:06


Quote:
Originally posted by 12AX7

Drill presses can't handle any sideways forces. You really need a metal-cutting or metal-spinning lathe to do it.


You're right, there will be a lot of sideways force. I'm sure it would work, but the drill wouldn't last long...

Quote:

Fortunately, there are several machine shops in any moderately sized city. You may even know someone with a lathe and not know it.


Trust me, I would know. And they would know I knew, since I would be camped out there permanently :-)

[Edited on 17-4-06 by Fulmen]
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[*] posted on 17-4-2006 at 14:56


BTW, you can get live centers from http://www.mcmaster.com/.

Come to think of it:

The main problem with sideways force on a drill press is, the chuck is held in the spindle with a taper. No bolts, just a steel cone worked up into a tapered hole. The shallow angle and elastic tension (from wedging it in) keep it in place for thrusting and rotating forces, but pulling and lateral forces tend to pull or walk it out of place and then you get a drill chuck spinning at 600, 1200, 2000, 3000 RPM and you don't know where it's headed! But with a strong downward force, it should be held in place not too bad. Also, cheapo drill presses are flimsy buggers, so with a firm live center at the bottom, it should be relatively safe as far as lateral force is concerned.

A big weight on the crank on the drill press might keep it in place, but mind also that drill presses are for drilling, not pressing. The rack is only going to take so much force before it bends or breaks, and it seems to me you'll need a reasonable force to keep that sheet in place.

Although you've got a good point, freshly annealed copper IS hell-ass soft. It's almost like lead. But once you get it moving, it hardens like nuts and you have to anneal it a lot of times, as you've discovered.

Hey, it would also be interesting to see a punch and die set, turned from steel billet, to press these cones. Just another few hours of machine time to cut them, and it's easy enough to bore things within a few thousandths on a reasonable lathe, to my knowledge.

Tim




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[*] posted on 17-4-2006 at 16:04


Quote:
Originally posted by 12AX7
But with a strong downward force, it should be held in place not too bad. Also, cheapo drill presses are flimsy buggers, so with a firm live center at the bottom, it should be relatively safe as far as lateral force is concerned.


Yes, I thought the same, the drill presses I've worked with have a long lever which allows a lot of force to be applied. More than enough to firmly clamp the sheet metal.
Another thing that aids in a secure fit of the sheet metal is the slightly rounded curve in the contact area between mandrel and contra mandrel.
And again, surprisingly, there is very little force involved here, in both clamping and working the coppersheet. Copper is one of the softest materials that can be spun. The tremendously fast work hardening is annoying though. You can make about 4-5 strokes in which no force at all is needed, like forming a sheet of lead, and then suddenly it won't do a thing anymore. :o
I needed 4 annealings for the last cone, but I think it can be done much faster still.

Quote:
Originally posted by 12AX7
Hey, it would also be interesting to see a punch and die set, turned from steel billet, to press these cones. Just another few hours of machine time to cut them, and it's easy enough to bore things within a few thousandths on a reasonable lathe, to my knowledge.
Tim


The punch and die technique could work for a hemispherical shape, but any more pointy-shape would punch right through the soft copper. Moreover, would you need to make a mould and contramold out of a very strong material like steel. Also should they fit together perfectly, which is only doable with a precision CNC metal cutting machine. (Hollowing out a complex shape like a cone out of a solid bar of metal is really difficult to do with a hand operated lathe, specially if it needs to fit together perfectly with the pressing mandrel)

I also considered slower hydraulic pressing, but than you need to allign the whole pressing rig (mold, contramold, and hydrolics) within the same scale of precision. With metal spinning, you need only to center your mandrel well. And if it doesn't you can sand the polyester mandrel quite easily down until it is perfectly centered. The polyester material also makes it alot faster and more versatile than pressing I think. A mandrel made from polyester costs almost nothing and can be made in less than an hour in any shape you want it to be.

[Edited on 18-4-2006 by nitro-genes]
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[*] posted on 17-4-2006 at 17:54


Quote:
You can make about 4-5 strokes in which no force at all is needed, like forming a sheet of lead, and then suddenly I won't do a thing anymore. :o I needed 4 annealings for the last cone, but I think it can be done much faster still.
---------------------------------------------

I think you might be able to work it longer before annealing if you keep your copper cold where you were working it. I have a cool mist unit and thought it might find good application here. It also would provide lubrication if one wanted to add a water soluble lube. Otherwise a spray of water/alcohol mix would keep things cool.
http://www.cartertools.com/sprakool.html
http://www1.mscdirect.com/cgi/N2DRVSH?PMSECT=2003608
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[*] posted on 17-4-2006 at 18:19


I don't see why you couldn't run a boring bar on the compound and run it in at an angle. Just set it the same as the punch piece, measure the diameter with allowance for the sheet. AFAIK, an hemisphere could be made with a circle cutter or cherry attachment (I always forget how the latter works).

If it's too pointy and tends to pierce, you could make two die sets, one to form the wide diameter and the other to finish the piece. It doesn't have to be in anything too hard, tool steel is only if you're making a hundred thousand or so. You could get away with, heck, get away with oak, or any dense, hard wood, for maybe a hundred cones I bet. Aluminum would be better, at least if it's a good hard alloy, maybe 7075-T6? Same process for cutting any of these including say, steel or cast iron (ooh, messy!).

Heh, using a steel bar and a hole in a chunk of aluminum, a not very well fitting hole mind you, I've punched holes in 24 ga. steel sheet. Not good holes, and not many, but holes... :P

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[*] posted on 17-4-2006 at 18:24


I think perhaps pressing the freshly annealed copper using a vice might work. "rough" it first with your hands, and then press nicely with the vice, which can put out a lot of pressure without a problem. Wouldn't be too hard to make two "molds" out of wood or plastic.

I like the drill press idea as well, I will definately try it if nobody else has by the time I've gotten some copper sheet.
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[*] posted on 18-4-2006 at 01:26


Quote:
Originally posted by ordenblitz
I think you might be able to work it longer before annealing if you keep your copper cold where you were working it. I have a cool mist unit and thought it might find good application here. It also would provide lubrication if one wanted to add a water soluble lube. Otherwise a spray of water/alcohol mix would keep things cool.


This was my idea too at first, but when properly spun, the copper becomes no more than hand warm maybe. I tried cooling with water, but to no effect unfortunately... :(
I think it's purely the pressure applied with the tool that rearanges the perfect raster of metalatoms and makes it more brittle again.
I do wonder why copper spun in the industry does not have to be annealed that often. I found some moviecllips in which they spin copper into much more complex shapes without 1 further annealing. :o

Maybe the copper they use is purer quality?! Mine is pretty pure already @ 99%...

[Edited on 18-4-2006 by nitro-genes]
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[*] posted on 18-4-2006 at 06:46


The "drill-press" concept is also beset by the lack of a tool guide. This is very important to proper spin control. I think it would be possible if one used the edge of a very large vise but again; not as easily as any lathe. I have a wood lathe. And tried it w/ Al and used a wood mandrel. Quick and dirty set-up, just to see what would happen....it works. However a wooden mandrel is not as well suited as it's "grip" is not as adhesive as what was shown, I believe. But Al is not what I wanted to use in the 1st place as I do have some copper. The soft, pure Al that is used suffered from many issues not to mention inconsistent pressure of the toolbar. This thing can be done. BUT the question I have is to what degree is it appropriate? If composed of the size that makes it useful I would end up with a rather large bowl. Needing about a 1/2 pound of energetic material. It needs to be scalable. I would think and that takes some thinking.....I tried a small (2") one and it just doesn't work as well. There needs to be a middle ground. If worked with; this concept could be a winner but the size issue is something I am really wanting to work with.
It DOES make some nice bowls however.




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[*] posted on 18-4-2006 at 08:14


Quote:
Originally posted by quicksilver BUT the question I have is to what degree is it appropriate? If composed of the size that makes it useful I would end up with a rather large bowl. Needing about a 1/2 pound of energetic material. It needs to be scalable.


Nice to see more people give it a go... :)

With the right sheet material and tools, you can go really small...The cones I made had a diameter of only 2,8 cm and would require about 20-25 grams of HE at most...I have no doubt that with some size adjustments to the working tool, even smaller cones are possible! (bigger is clearly no problem) This weekend I will have more than enought time to experiment a little with different shapes and sizes.

The macro setting on my new digital camera clearly works! :D


I can't wait to give them a try...Unbelievable that I've always had a good source of HNO3, but now the new delivery has failed to arrive...:mad: I still have some NM, but it sucks with these diameters. Time to get my vacuum distillation equipment out of the dust again.:)

[Edited on 18-4-2006 by nitro-genes]
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[*] posted on 18-4-2006 at 18:34


With the punch and die idea, you could heatsink the center of the copper disk with whatever you're using to hold it, so it stays cool and is not annealed while the rest of the disk is. This would keep the center strong but allow the rest of it to stretch freely when force is applied, and would remove the potential problem of piercing the copper when forming the cone.
It will probably need to be secured at the edges of the die or it will simply get pulled down instead of stretched. If the die is metal then it can serve as a heatsink for the outer part of the copper (where it is secured) so that part remains strong as well as doesn't break when pressure is applied.
You will wouldn't be able to use a sharp point for pressing the sone, but I think a shape similar to the one used with the lathe would work quite well in this situation.

With the lathe, could you simply apply a propane torch and use a metal hold to keep the copper soft while to press it? I don't know how you could keep friction low as the parafin used would simply burn but it would prevent the need from constantly having to stop and anneal the copper cone several times during each run.
I don't think it would need to be kept that hot to have the copper remain ductile during the procedure.
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[*] posted on 18-4-2006 at 19:18


I constructed a conical punch and die a few years ago for making copper cones such as this. I tried flat sheet but it was difficult to work without punching holes in it. Just too hard to gather up and shrink all the edge material.

What I found that worked better then sheet was copper sweat caps from plumbing supply or hardware stores. They are nice and thick and come in many sizes. Of course since they already are cup shaped the amount of forming needed is considerably less.

coppercap.JPG - 6kB
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[*] posted on 18-4-2006 at 19:26


Eh, I don't think you can heatsink the center while annealing. Copper is impressively conductive stuff.

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[*] posted on 19-4-2006 at 03:07


Pressing cones in a single stage sounds like asking for problems. I think you'll have much better luck with a series of punches with diminishing radius at the end, this would reduce the likelyhood of simply piercing the disk.
And as for the idea of using a heatsink while annealing I agree with 12AX7, copper is way too conductive for this to work.
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[*] posted on 19-4-2006 at 04:47


The whole process of pressing is just more prone to result in errors in lateral symmerty. In my tries with pressing I got a lot of problems too...

One is that when you start to press even slightly off-center, this error will result in on side of the cone being more strechted than the other, thus having more material on one side than the other...
but even with everything perfectly centered I noticed that the copper under pressure has difficulties in "sliding" correctly into place. The mold, or coppersheet is more rough on one side, resulting in one side of the sheet getting stuck. (not very clear explanation) The whole pressing mold should be finely polished and lubricated to overcome this problem.

The beauty of spinning is that, when correctly done, errors in wall-thickness only exist in a circular ring shape manner. But since this does not effect the lateral symmetry of the cone, they do not disturb a proper collapse and jet formation during detonation. Pressing definitely is possible, but if you do have a lathe to make the pressing forms, you're better off with the spinning technique I think..

Btw: spinning is just too much fun really :D

[Edited on 19-4-2006 by nitro-genes]
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[*] posted on 19-4-2006 at 07:03


Quote:

What I found that worked better then sheet was copper sweat caps from plumbing supply or hardware stores. They are nice and thick and come in many sizes. Of course since they already are cup shaped the amount of forming needed is considerably less.



THIS IS EXACTLY what I was thinking of when I read that post. I actually have a boat load of these damn things. I wanted to turn them on a lathe - fusing the two concepts of punch and lathe.....I can't see how one would "cone" these shapes with any degree of consistency using only the strength of a human hand and hammer, however.
And spinning IS fun. I have made so many things on a lathe that it's just a physical addiction now.

[Edited on 19-4-2006 by quicksilver]




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[*] posted on 19-4-2006 at 13:42


It is a bit confusing maybe to post them now, but with my new camera I could finally take some pictures of my results with the 3 cm diameter glassliners made out of those candle lightbulbs...:D Nothing really of much importance, only that I discovered that more than 1,5 times CD standoff results in a much smaller hole volume with these liners...


It appears strange to me that the 3 CD standoff with the PETN/Pib plastique had the same penetration as the 1,5 CD standoff with the same liner and plastique. Because the entrance hole looks like a mess with the 3 CD standoff, and the volume of the hole it made was also considerably less...
All the other "holes" are my attempts with the 0,2 mm copperfoil. :(



This is a closeup of the deepest penetration with the 8/2 PETN/NM composition:



And the really slight bumb it made on the other side:



Oh, btw, I've managed to produce about 100 grams of PETN, with freshly distilled HNO3, still have to recrystalize, dry and make it into plastique though. I also have the opportunity of using PETN/NM or PETN/NG, but with these amounts of HE, plastique is much more safe and practical. (After crystalisation I can directly add the Pib/oil coating laquer to the water wet PETN, so no need to handle dry PETN)

I think monday will be the day! :P

[Edited on 19-4-2006 by nitro-genes]
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[*] posted on 20-4-2006 at 06:53


Frankly, I am grateful you took the time to post those pics as they contribute to the knowlege-base (from my perspective certainly) quite a bit.
The more I read on this subject the less I feel I know. So many authors state that the subject is still in it's infancy as some phenomenon are just unaccounted for. Lord knows why certain materials are more effective than others in certain situations. And WHY glass should be so damn effective in place of a ductile metal is still debated. The stand-off does have a formula that appears to be meaningful but I have now found that centering the cone-shape has been questioned. One author offered that glass imparts granualtion to a greater degree than many would expect within the jet. If this is so then the "mold & powdered metal" concept makes a great deal of sense. I also read that tungsten is one of the materials of choice but that metal is out of reach. Nickel powder is not tough to find but turning or even working either of these is frought with expense and specialized tools. Silver is rated well but again; just too much trouble to experiment with. Perhaps cone shape has more influence than most anything else in a generalized perspective? I see less trumpet shaps and more simple cones (but differing on occation from 60 degrees). Surely I would think that the thin glass in a lightbulb is less effective than copper..... I am trying to determine what was used in WWII as that time period was beset with cost-savings and mass production. What is "state-of-the-art" today is almost worthless from a personal-knowlege perspective as it just is impossible to duplicate. As well as being caught up in the military contract cost over-run scam.
HOWEVER...I found a powdered metal shaped charge patent that has more flexability to it than I have seen in a long time. This would allow experimentaion with nickel or copper powder and an alteration in shapes (from 1966).
The damn PDF was above two Mb (it's 10 pages) so I couldn't upload it. - if you have any interest it's June 14, 1966 US3255659. I didn't want to leave anything out of it (many illustrations). In that patent the use of nickel or copper powder is shown to be a substantially easy liner to work with and reportedly successful.

[Edited on 21-4-2006 by quicksilver]




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[*] posted on 22-4-2006 at 14:16
My first shaped charge


Well here it is!

Windows movie maker severely sucks ass so I apologise for the crudity of the video. I tried to get the files into premiere but bynumbers's digicam isnt compatable with adobe and it was having none of it!

As you can see the SC did not penetrate the steel to any appreciable degree and by the look of the end of the vid, the pitting that can be seen is probably due to Al spray as apposed to Al jet that we were hoping for!

Although obviously disheartend we have to try to draw conclusions from this failure to do better the next time. I can think of several reasons for the lack of 42mm penetraion. They are as follow:

1) The cap was shit. I tried to rush my HMTD synth to meet a deadline and ended up with just 0.25 grams that didnt even half fill the small plastic tube I had in mind to receive it. This meant that I had to fill the remainder of the cap with blutack which caused problems in itself!

2) What little HMTD that I DID have was Shit! Not only did I not have time to totally dry it, but also it was heavily contaminated with filterpaper fibres scraped away in my frantic efforts to maximize the pitiful yeild!

3) The Al cone I ended up using was shit... and a badly obtuse apex angle in my efforts to increase what little headheight I had above the cone. The first one I made had a better angle but sprang a leak... BOY was I cursing!

4) The shit cap I threw together in my rush to have it all ready on time had to be pushed so far into the charge to get the HMTD down to the level of the EGDN that it was vitually touching the top of the cone... Headheight TOTALLY out of the window!

5) Finally, I screwedthe stand off distance! You can see this in the video. I WONT be attatching the legs with elastic bands next time!

Anyway... here is the video for your mocking pleasure! Any constructive comments would be much appreciated as always.

Bye for now!


http://media.putfile.com/Fuckup

[Edited on 22-4-2006 by Deceitful_Frank]
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