Marsh
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Det Cord
I realize this topic is more for practical application than anything, so feel free to remove it if you don't think it is a suitable topic here.
I for one was tempted to post this simply because I haven't read yet about a simple means of one producing an effective det cord.
Over on RogueBan there is a topic about det cord, in which no one seems to have perfected it so to speak. One speaks of air compression, but that
seems of lesser desire as air does not always compress a powder as uniformly as ramming with an object.
One person there suggested soaking a rope in MEKP and laquering, which to me is pointless because the rope is obviously inert and will greatly
decrease density and performance of the MEKP. A flexible thin-wall teflon/nylon tube filled with MEKP and sealed ends does sound feasible, but the
idea all together of a primary detcord is a bit scary.
So (and this is so simple it has to have been tried or crossed someones mind), why not use a teflon or polypropylene tube, with a long length of
brass, steel, or aluminum rod to slide into the tube to ram the PETN with? I can't see there being any reason not to achieve high densities, so long
as it is rammed every few cm and/or possibly plasticized just a bit.
Of course you could kink a 4m tube in the middle, pack with a 2m rod, unkink and then pack from the other end for a 4m length of detcord.
Any thoughts on this?
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Axt
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The easiest way is analogous to what pyrotechnic geeks refer to as "sticky match" which is a length of tape with a line of explosive up the centre, so
simply substitute blackpowder with a high explosive then fold the tape over to seal it up. I've used this to produce effective det-cord, this is the
only movie I have of it: http://youtube.com/watch?v=uSnxUuGlER4
Its best to use a crystalline explosive, small needles of ETN crystallised from acetone works well as they hold their place in the tape very well.
Dont try it with a fine powder as you'll end up with non-sticky tape.
Google for "sticky match machine" if long lengths are desired though you will need the right crystal shape and size to allow it to flow easily.
[Edited on 14-7-2007 by Axt]
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nitro-genes
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Ramming powdery PETN sounds a bit scary, pressing sounds more appropriate. PETN still is one of the more sensitive secondaries around! 
The sticky match idea is a great one, do you know how well the resulting detcord resist flexing etc?
Another option would be to alter the crystal shape in such a way that the crystals would be free-flowing, dense and small enough to be loaded easily
by gravitational flow into the tube. As you can imagine, most likely the same procedures I send to you by u2u will apply here as well.
The only difference with commercially used detcord is that the PETN is crystallized from a solvent to produce freeflowing crystals. The
crystallization procedure is so efficient that the thus recrystallized PETN has no trouble flowing through a 0.2 mm diameter tube from gravity alone.
I was unable to find any detailled information about this other than that the degree of freeflowing crystals (hexagonal agglomerates) was closely
related to the amount of di-PEHN impurities present. (Some Dupont patent IIRC) Detcord made this way would withstand quite some abuse because of the
freeflowingness of the crystals inside, although it would be more work than the sticky match idea.
Plasticizing is not an option, I can't envision how you could press the resulting plastique into a tube of a only few mm's diameter.
There are not many other explosives that are suitable, in the best case you are looking for low sensitivity with small critical diameter, properties
which usually don't go hand in hand. Then liquids would provide the easiest loading properties, though NG and EGDN suffer too much from LVD at these
diameters, as well as beeing too sensitive. I think PETN, RDX, ETN and MHN would be the only commonly available candidates for reasonably safe and
small diameter detcord.
[Edited on by nitro-genes]
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Marsh
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I called it "ramming", but I picture it more as pushing the PETN down the tube in that manner, but simply pressing it at the end. No I would not
actually ram the dense stuff with a metal rod! (End up possibly with a pretty long rod projectile fired out, yikes!)
I think it sounds quite effective, actually. I ordered polypropylene and nylon tubing to try this with. The rod should slide more easily in the nylon
and fits that one closer. The other will be a little more loose just to experiment.
I think the poly may work a little better than nylon as the det cord material because it is much more flexible (20mm bend radius vs 70mm). So cutting
small objects (tree branches for instance) will be more easily wrapped without taping.
Both materials are of course resistant to MEKP (and clear to see things), so I will give a shot at filling one with MEKP as well, for performance
comparison of the two. Will probably tape each on plywood in an 'S' pattern to see if they slice it.
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Sickman
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Marsh,
10mm, thin walled plastic tubing of your choice.
A large pot of hot water.
And a few pounds of etn.
The etn need not be filling the entire inside of the tube, but 5/6 full is fine, even if the tube gets folded in half and the cast etn is broken away
from the the rest of the elongated body of cast etn it will not fail to high order. Such a cord, is every bit reliable as military stuff.
It's one of those things I'd bet my money on.
P.S. Clear plastic tubing is ideal for observation during the casting process! Another thing. Cutting the filled cord with scissors by gently applying
pressure in a place where you have already "broken" the cast etn by folding the cord in half at the location desired to be cut is no big deal and
doesn't result in explosion. However you're best off to use a shield when cutting the cord just to put safety first.
Loading a cord by pressurized air or ramming/tamping, doesn't seem as logical to me if casting is an option. Think VoD, a minumum of equiptment, and a
more consistent density!
[Edited on 14-7-2007 by Sickman]
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nitro-genes
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There are two problems with casting...
First one is how to avoid the ETN from becoming solid when it has travelled only a few centimeters down through the tube. You would have to preheat
everything, inlcuding the tube to avoid this. The resulting liquid however is pretty viscous anyway, capillary forces would make it hardly run down
the tube unless you use very large diameters. For the suggested 10mm diameter tube you would need about 110-120 grams per meter! I would discourage
anyone from using these amounts of ETN at 60 deg C...
The second problem is that the ETN would cool down as an continuous amorphous solid. The lack of crystal surfaces makes that you get the same LVD
problems as with NG or EGDN. Ideally you need the explosive to be the finest powder possible while still attaining a high density.
It's not that hard to make even small crystals freeflowing. Simply recrystallize the PETN/RDX/ETN/MHN into small needles (be sure there are no lower
nitrated PE impurities left during crystallization, these affect crystal morphology in a bad way!) and put them into a blender with at least 3 times
the weight of water compared to the PETN and spin for about 10-15 minutes. The resulting powder is almost as fine as flower, freeflowing and has a
high bulk density.
Maybe the easiest method of making detcord would be to take a flexible plastic tube and cut it open over the entire length. Then you take a bowl where
you put in your powdery explosive and push the tube open with your fingers to press in the explosive. With some practise I bet this could be done very
fast. Afterwards you put some tape around the tube to make it water resistant again. The 4 mm ID aquarium tubing would need about 15 grams per meter,
with 2 mm ID beeing somewhat the lower limit for PETN with 3.5 grams per meter...
[Edited on by nitro-genes]
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gnitseretni
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How do you make your PETN as fine as possible? I always recrystallize with acetone.. is that the best way?
EDIT: ah crap.. my apologies.. it's right there in nitro-genes post  Not sure i
have the balls to put it in a blender though 
[Edited on 14-7-2007 by gnitseretni]
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nitro-genes
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Working with small amounts only is such a common habit to me that I forgot to mention that you shouldn't use the blender technique with very large
amounts. Just do small amounts at the time, like maybe 20 grams and use enough water with it.
Just shake the blender well by hand just before turning it on, this to make the PETN suspend in the water and not as a layer at the bottom when the
blades start spinning. All explosives have a certain percentage of inerts that can be added and still be detonable. RDX can handle about 30% inerts
while still beeing detonable with an #8 cap, while PETN can handle about 35%. With increasing water content the sensitivity quicky drops further, with
more than 40% water rendering PETN pretty much insensitive. With 3 times as much water as PETN there is virtually no risk of detonation, physics just
won't allow it!
The process is very similar to the industrial way of producing free-flowing crystal shapes, though at slower agitation rates than with a blender, got
to give you that. Take a look at US4065529 and the like...
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Deceitful_Frank
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Recrystalized Detonating Cord
A 60cm length of 2-ply toilet tissue with offset perforations and 3 gram mass was laid flat on a work surface and folded twice to give a strip of 8
layers and width approx 2.5 cm.
6 grams of pure dry ETN recrystalized from denatured EtOH was then placed into a seperated 20ml syringe, nozzle sealed with a little blu-tack. 15ml of
denatured EtOH was then poured in through the top, the plunger was replaced and the whole deal shaken vigorously causing some of the ETN to dissolve.
A preheated tea cup was then filled with water at 60 celcius and the syringe placed inside to warm through, removed and shaken several times. After a
few minutes a hot near-saturated solution of ETN in EtOH was obtained.
The syringe was then lifted from the hot water and the blu-tack removed. In one sweeping motion around half of the solution could be squirted over the
entired length of the tissue paper before the nozzle clogged with cooled recrystalized ETN. The blu-tack was reattached and the syringe placed back
into the hot water for abother minute and the process wass repeated to empty the syringe.
After a minute or so capilliary action had spread the solution evenly throughout the tissue paper and the ETN had precipitated throughout as a pale
beige solid. The whole deal was left to cool and dry and folded once more to give a length of stiff "paper-mache" of approximate mass 10.5 grams.
An hour had passed under my fan and I'd figured 1.5 grams of EtOH in my det cord could hardly hurt and growing impatient, I proceeded to the next
step.
A strip of thin Al foil was selected 60cm long and 5 cm wide. This was placed under the ETN Tissue, folded over a compressed with my fingertips. The
Al foil was added with a view to increase the cord's durability, its tensile stregth and also to contain any loose ETN crystals which could be lost
during handling.
Finally two layers of stretched PIB taped were added to compress the core and give water resistance and a more professional look.
I have attached two pictures blow for your perusal
http://www.putfile.com/pic.php?img=5991510
http://www.putfile.com/pic.php?img=5991509
I tested my prototype yesterday using 0.5 grams of ETN taped to the side at one end for intiation. As you can see in the clip I cut and refastened it
midway along its length to see if it could propurgate to itself with a 3 cm overlap... the results were hardly inspiring but I am not too put off. I
can think of a few reasons why it failed to detonate and I managed to recover 50cm of the length for further testing
I will list possible reasons for failure below but as always, any other ideas would be gratefully received!
1) The high level of inerts within the central core. Including the 1.5 grams of EtOH left unevaporated... 43%? In fact, 30% of the mass of tissue was
unnecessary to absorb the solution and with care I could reduce the inerts to 25-30% by tweaking my solution of ETN in EtOH.
2) Weak initiation? Half gram of ETN was just hand-pressed into a penlid and taped to the side of the cord.
3) Two layers of PIB tape gave the cord a sturdy and weighty feel but maybe prevented the shock from the ETN in the cap from reaching the diluted ETN
in the cord? The cord is 7mm in cross section but the core of ETN is just 4mm thick.
4) The double layer of PIB compressed the diluted ETN core to a density that rendered it insensitive to the initiation it was given?
[Edited on by Deceitful_Frank]
[Edited on by Deceitful_Frank]
Attachment: Movie_0002.wmv (409kB)
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Marsh
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Frank,
I think it is surely a combination of things you present which led to its failure.
I personally feel that the recrystalized paper provides too low a charge density (mainly too small of intimate contact between the crystal surfaces),
and that it alone occupies too much inert mass.
On the other hand, material thickness between a cap and energetic can be a problem here too in your experiment. I have had pure PETN packed in a paper
tube (about 1mm wall thickness) fail to initiate from a 1g PETN det taped to the side of it. Ripped the tube apart and spread PETN around. So even
that small thickness of paper was enough cushion to hinder the shock from the cap (when in contact with the PETN there is never a failure of course).
What I would do is remove tape from the area you are trying to initiate so there is very little cushioning if any. Or, use a clean cut end of the
cord, and tape the det to it at a 90 degree on the very end to make a 'T'. This way the shock directly impacts the ETN itself with no barrier.
I think that if you can get the cord to look this good using paper, that you should simply wrap the tissue paper around loose ETN crystals, and wrap
again in foil/tape like you did here. I'm sure it is easier said than done as crystals will want to move around. But, I think we are starting to see
(provided this cord just won't go) that the best option is in fact a pure core of the energetic without inerts.
[Edited on 15-7-2007 by Marsh]
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texaspete
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How about using a visco machine, but using something like PETN instead of blackpowder?
http://www.truetex.com/visco.htm
http://pyroforum.nl/index.php?s=952c7c6698531018d1181802f4a8...
Visco is a little thin, but it might be possible to scale it up.
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Deceitful_Frank
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Well,
I just returned from my test area to report that a 4mm column of ETN with 43% cellulose slightly damp with EtOH at a density of around 1.5g/cc CANNOT
be detonated by 500mg of pure hand pressed ETN.
I set the experiment as before but this time the ETN in the blasting cap was in direct contact with the freshly cut end of my detonation cord. The
cord did not fire.
In fact I even took a lighter to it and then placed it over a small fire of matchsticks but all I was rewarded with was a pathetic fizzing puddle of
molten PIB and ETN
I had such high hopes for this technique and was sure it would be a great way to make a good powerful and DURABLE detonation cord. If I can find a way
to produce an absorbed recrystalized core with just 20% inerts then I will try this method again but reducing the amount of tissue paper just defeats
the point.
Maybe with its tiny critical diameter and even higher sensitivity, MHN is the way to go but yeilds are really shit without WFNA and compared to ETN,
it takes much more work to render it stable enough to store for any reasonable length of time.
I like nitro's idea of longditudinally loading a cut length of flexible tube. Perhaps if you were to select a one metre length of 10mm ID flexible
tube and using a scalpal, remove say a ribbon of plastic that amounted to 25% of the arc along the entire length. The exact amount to remove would be
an object for experimentation but it would be easy to load evenly with finger tips. You would then wrap with cling film to hold everything in place
while you add a final coat of PIB tape to compress and join up the cut edges of the tube to provide a perfectly even density throughout! It would be
easy to link multiple 1metre sections together.
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Marsh
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An upscaled visco machine sounds like it should definitely work, but you would imagine densities achieved to be sacrificed, as it simply pours a
powder into the weave. Some form of compression is really needed for tolerable performance in the det cord.
I don't know how tight the weave could become, but if someone has one of these machines, I would love to see the attempt!
Frank, don't give up. Try another test without the variable of having damp ETN. You want the cord as optimal as you could make it, and fortunately a
little more patience would have made this test a bit more optimal. Try to crystalize out as much ETN onto the paper as you can with slight excess. As
far as your wrapping with the PIB tape, that looked good to me!
[Edited on 15-7-2007 by Marsh]
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franklyn
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Detcord in 10 easy steps
JEeez - Has anyone actually made a length of cord ?
Unless your explosive is the consistency of syrup and it can be syphoned as a
uniform bead without voids or bubbles , filling a tube is just a pipe dream unless you
are prepared to join two foot sections , the limit to which you could possibly fill a tube
with anything more viscous using a chaulking gun. Apart from the unpleasantness
of working with a hot melt the phase change when this solidifies means cracks
will surely develop.
It's not incidental that commercial detcord is extruded with plasticized explosive.
An explosive must at least be plastic like dough to be easily worked.
If you still want cordeau or primacord , you'll have to roll your own using tape.
You need a tape that is pliant and tough 2 to 3 mil , 2 inch width , if it tears easily
it's useless. Tapes come in 15 , 18 , 20 , 36 , 55 , 60 , 72 yard rolls , depending on maker
1.25 and 2 inch core spools for the smaller rolls and 3 inch core spools for the largest.
There is a universe of tape from which to choose , here is a product finder
http://tapeinfo.com/TapeInfo/SingleCoatedFilmTape.aspx
These are expensive , over 20 cents a foot , but the best always is.
For a given length of tape you will be able to roll a length of cord half that length.
That means 40 cents per foot of cord , just for the tape.
Dupont Tyvek brand , 2 inch X 18 yards , Polypropylene fabric seam tape
Used in house construction look for it at building suppliers
http://www2.dupont.com/Tyvek_Construction/en_US/products/res...
http://waterdamageprotection.com/Merchant2/merchant.mvc?Scre...
http://en.wikipedia.org/wiki/Tyvek
If you wonder what Tyvek is like , inspect the Express Mail envelope at the U.S. Post office
http://upload.wikimedia.org/wikipedia/en/thumb/f/f6/TyvekExp...
another _
Permacel P99 brand , 2 inch X 72 yard , Polyester / celulose fiber reinforced packing tape
Used as a box sealing tape look for it at hardware and office supply stores.
http://www.findtape.com/product218/Permacel-P-99-Polyester-F...
1.
To begin you will have to find a suitable molding or channel extrusion having a groove
of minimally 3/16 inch wide and deep , and round on the bottom inside , with lightly rounded
edges. If you have the wood working tools several grooves can be routed into a length of
a 2 X 4 inch wall stud.
2.
These grooves are the mold to be filled with explosive to produce a uniform bead of
material from which to fabricate the cord. Using an aerosol L O W Tack ( lightly sticky )
contact adhesive , spray the grooves in four or five places. As depicted in drawing - A -
using 2 dowels press a sheet of wax paper into the grooves. Leave the dowel in the first
groove to hold the wax paper in place while you press the the wax paper into the groove
next to it. Then remove the first dowel to press the the third groove , and so on.
3.
Using a dough rolling pin work plasticized explosive into the wax paper covered grooves.
Neatly slice the surface with a knife so that only the grooves are filled , without damaging
the paper. Unless you really know what you're doing stick to a known PETN or RDX
composition.
4.
Mark off a strip along the edge of your work bench just in front of the mold that is
1 3/4 inch wde using masking tape , and spray this exposed strip of the bench with
the same low tack contact adhesive used to hold the wax paper on the mold.
5.
You will now tack onto this sticky surface of the bench , the back non adhering part
of the 2 inch tape so that the sticky side remains up , leaving one edge hanging clear
off the bench by a 1/4 inch. Do this carefully drawing the roll tilted along the sharp edge
of the bench , poking down the tape with a pen onto the sticky surface on the bench.
IMPORTANT ! choose a direction you prefer NOW , here depicted in drawing - B -
it shows how you will later proceed to roll the tape working from right to left. The tape
M U S T be unwound in this same direction , in this example ending on the far LEFT.
DO NOT cut the tape at this length if you will be using the whole tape , just leave the
roll at the end to repeat this same proceedure later.
6.
Lift out the wax paper in the mold to remove one bead of explosive and turn this over
flat side down onto the top edge of the tape on the bench ( farthest from you ) and
stick it onto the very edge of the tape leaving no border and a few inches away from
the start of the tape. See drawing - B -
7.
Begin by forming a tube by holding a 3/16 inch drill bit on the upper right corner of the
tape at a 45° degree angle and roll it towards you.
The tube M U S T be held at a near constant 45° degree angle to the edge of the bench !
The width of the tube is controlled by the angle at which you hold the wrapped portion
to the edge of the bench.
As you wrap , the tape will lap the explosive bead and envelope it forming the cord.
Every few turns the explosive bead may bulge ahead of the overlapped tape if the wrap
is too tight. If the explosive bead bulges ahead , make the angle a litlle steeper but not
more than 50° degees to the edge of the bench to make the tube a little wider at that
point , but always returning to the optimal 45° as you continue to wrap. The distance
from the exposed edge of the tape from each turn wound in the cord to the next should
not be more than 5/8 inch.
Since this is done by visual judgement , practice and experience matters a lot wether your
detcord ends up looking like a lumpy pregnant snake or not.
8.
Once you come to the end of this short run you need to stop wrapping before all of the
explosive bead is covered , leave at least 2 inches exposed. Now pick up the roll of tape
and carry with it the cord you already made over to the far right side and lay out again
another length of tape exactly as before.
9.
Once again remove another bead of explosive from the mold and fix it to the tape.
With a razor or sharp knife cut away a wedge off the end of those two inches you
left exposed on the first run of cord and lap the new bead of explosive right up on it.
Now cut away a second wedge from the new bead to trim the excess , as seen in
drawing - C -
10.
After the the whole length of tape has been used up ( or only the length you wanted )
pick up the end of the cord where you finish and hold that firmly in one hand ,
with a cloth in your other hand draw this along the cord applying a slght tension.
Do that for the whole length of the cord.
11.
If you plan to store this cord you can apply a finish coat of polyurethane wood
varnish to seal and protect the tape from abrasion. If you really need to , and I
can't imagine why , unless you plan to rappel on this , another wrap of tape can
be appllied over the first but this time going around in the opposite sense. If it
wrapped counterclockwise before , it should now be wrapped clockwise.
Hope this helps
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12AX7
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Regarding spiral wound tubes.
If the material (adhesive tape, pasted paper, etc.) goes on parallel, the diameter increases, because the geometry is the same as a flat roll that's
been pushed axially to give a helical shape. If you form the tube over a winding mandrel (obviously doesn't work well with adhesive tape!) so the
incoming strip lays flat between the previous turn and the mandrel, the extra diameter of the previous turn will cause the angle to process until it
becomes perpendicular with the mandrel. If you force the angle and diameter constant, you must include a diagonal fold somewhere to relieve the
excess material.
Tim
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texaspete
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Marsh, how much compression is needed? Visco has to be fairly tightly packed to achieve a consistent burn rate: any loose packed areas would act like
quickmatch.
The funneling and winding should cause some compression. Maybe the machine could be modified and another, tighter wind could be performed on the
chord.
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nitro-genes
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The density of the PETN core in primacord is about 1.15-1.2 g/cm3. This gives a VoD of around 6600 m/s. Compression to achieve this density would have
to be minimal if your crystal fraction is spherical enough. Bulk density of blendered PETN is about 0.8, depending on avarage crystal size. With only
very little compression you can get to 1.2 easily. The difference between acetone crystallized and crystallized+blendered is quite dramatic. Only
crystallized from acetone the PETN forms a hard material (like bentonite does when making rocket nozzles) with only little compression, while the
blendered grade can be compressed quite hard and still run back out of the container.
With an extruded plastic bindered material you could go 7500+ m/s but it would have to be a very well made plastique in order to be used in tubes less
than 3 mm ID and be flexible enough to be knotted like primacord can...
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Marsh
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Tubing arrived today. As I expected, the poly tubing was just too soft for me to use the rod I had; it grips the rod too well. I will try a smaller
diameter rod as I think this is the preferable tubing to use for flex.
The nylon, being less flexible but harder material, worked perfect for packing with a tighter fitting rod. I managed to fill a 1 meter tube full of
pressed PETN, taking me over 2 hours to do! Definitely not for an impatient person.
I did learn how to properly do this, after I managed a few air pockets during the first half of the cord. For the first half of the cord, I was
pressing the tube into a pile of PETN, forcing more to press into the end, and then tamping it quite a bit to get the stuck PETN to fall. This was
more of a hurried way to get more into the tube quickly. While doing this, I was tamping large amounts that were in the tube to the bottom, allowing
air pockets to develope that I didn't observe until after packing with the rod.
Once I realized right at the middle of the cord there was a 1mm air gap I had missed, I decided I was doing this the wrong way. I then started sliding
the tube across the top of the pile instead of pressing into it. Each time I would swipe across the top to gather a little bit of PETN, I then tamped
each small amount all the way to the bottom, filling in any possible air pockets. Then, instead of every 2-3cm packing with rod, I starting
packing with the rod after every 1-1.5cm of loose PETN.
After I started doing it the correct way, ALL visable air pockets were eliminated and density seemed very promising.
So, I think the first half of the cord I did may perform like crap, but I believe the second half should do quite well. I'm hoping the shock will be
able to cross the air pocket in the middle. Before I det, I will lay the cord horizontally and tamp to get some PETN to fall within the gap.
The ID of the nylon tube is 4.8mm. It is somewhat flexible, but due to the nature of the nylon, I imagine it is stiff when compared to commercial
grade det cord.
I will hopefully tape it across a plywood board tomorrow and test the cord to post results.
[Edited on 16-7-2007 by Marsh]
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Polverone
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There doesn't seem to be much chemistry here.
Edit: or novelty.
[Edited on 7-17-2007 by Polverone]
PGP Key and corresponding e-mail address
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Marsh
Hazard to Self
Posts: 79
Registered: 28-7-2006
Member Is Offline
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Managed to get out and test the cord today on a piece of 1/2 inch thick plywood. It worked great, easily slicing its entire width.
Although this method is a slow one for me, it was about as close as I could manage to come to commercial grade cord. I will be using this method for
shorter lengths of cord, although surely a quicker method would be much more desireable than this one.
The video download is available here: http://www.sendspace.com/file/xi0c6u
Since it looks like this thread will be closing, I'd like to hear about anyones success with other ideas, so feel free to discuss them through U2U.
The arrow in the photo was simply to show me where the small visable air pocket was that I found in the cord, in case there was any noticeable effect
from it.
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