swervedriver Posted January 10, 2009 Posted January 10, 2009 (edited) Sequential_timed_Fuse_Bursts__Snail_Shell.avi Hi. I was wondering if someone knew where I could find information on how to make short duration time fuse for can shell inserts. I've read what little I could find on how some beraq inserts are timed using different bp binder ratios of gum arabic in bp. The sides of the beraq look like they are half pasted with bp prime, and I believe there is some kind of a punched hole in the side of the case underneath the bp paste of prime. I don't know what keywords to search google with to find similar effect shells other than the word "beraq". But here's an example video of how accurate some people can make them. What I can't figure out is how the heck they make the time fuse so accurate, to what seems like hundredths of a second sometimes. Small spolettes? Some how the timing is super accurate. Edited January 10, 2009 by swervedriver
Mumbles Posted January 10, 2009 Posted January 10, 2009 There are some high precision timefuse cutters around. Rich wolter offers one, for quite a hefty price. I've seen others where a pair of anvil cutters is modified. Normally a screw is attached. So with 32 turns per inch, you can cut time fuse to 1/32nd of an inch. This gives accuracy to about 1/10th of a second. Drilling back spolettes also works. I had always heard red gum in the BP, but gum arabic works too. If you go over to www.pyrosociety.org.uk there is a guy named Karlfoxmann who has pretty good success with this. He made a word document outlining it.
ST1DinOH Posted January 10, 2009 Posted January 10, 2009 silly question here but i'll just go ahead and ask anyway. rather than making the time fuses super short, couldn't you make them long and fast burning? the longer it is and the faster it burns the better you could adjust the time. some sort of visco thats protected on the outside from passfire, in a tube, accordioned upped inside the insert... wouldn't that work?
portfire Posted January 10, 2009 Posted January 10, 2009 I had always heard red gum in the BP, but gum arabic works too. If you go over to www.pyrosociety.org.uk there is a guy named Karlfoxmann who has pretty good success with this. He made a word document outlining it. I've found one of Karls posts explaining how it's done. "Ok heres what I use: Tubes: I hand roll them from 250gsm paper, 420mm long strip by 40mm wide. Rolled tightly and pasted all over. Former is 3/4. Then I paste normal printer paper over it, 40mm wide and 210mm long. When dry I seal with either hot glue or sawdust/pva mixture. A 2mm hole is drilled in the side slowly and I use soap to lubricate the bit to stop it messing up the inside of the casing. The formula is as follows: Standard BP 75 Potassium nitrate, 15 Alder charcoal, 10 Sulphur. This is milled to make it fast, I mill 100g for 1.5 hours as this makes fast powder in my mill. Once milled I add 5% Gum arabic, this can be changed to alter the speed of the burn but I would not go below 4% as it may not make the paste strong enough. The paste needs to look like black treacle so add enough water to do this. The paste is the pushed into the hole using a knife, you want to see a 2mm 'pooh' start to come out the delay hole on the inside. Now paste a bit more over the hole and dip the prime into grain powder. Once the paste has dried you can feel hoe strong it is! Now fill with flash and seal the other end. One note, I add pasted paper to either end of the casing to stop flame getting inside the beraq before it should." The link to the work document is dead, though I do have it somwhere if you want me to upload it?
MilkyJoe Posted January 10, 2009 Posted January 10, 2009 I believe I posted the document you are talking about in the Random Thread. It's Karl's paper on beraq inserts and it outlines the timing method. Found Here ~Milky~
portfire Posted January 10, 2009 Posted January 10, 2009 I believe I posted the document you are talking about in the Random Thread. It's Karl's paper on beraq inserts and it outlines the timing method. Found Here ~Milky~ Thats the one I was just about to upload it but removed the flash comps from the document, as they are some nasty ones in there
swervedriver Posted January 10, 2009 Author Posted January 10, 2009 Wow, thanks for the quick replies. Good info. That doc tutorial is really detailed, thank you for that Milky (and karlfoxmann). The pictures are worth a thousand words. ST1D, I also had that idea and was thinking someone could make that work. I figured there was another way that the pros used other than the carefully measured fast visco. That way could work if care is taken to protect the exposed fast visco from burst damage and untimely fire transfer from the burst along it's length. Mr. Mumbles, thanks for the tip on drilling back spolettes. I was playing with short small id spolettes but consistency to fractions of a second were baffling me. Using consistently pressed grains and a stopped drill press back to specific lengths for repeatable results sounds promising!
tentacles Posted January 10, 2009 Posted January 10, 2009 swerve: When you're drilling the grains, especially with power equipment, make absolutely certain there are no open buckets of stars, trash bags of BP hulls etc around.
swervedriver Posted January 10, 2009 Author Posted January 10, 2009 Thanks for the heads up tentacles. Really. After getting familiar with some of this stuff, I see how a simple cardinal rule of "think of any safety issues first" before trying something new can potentially be overlooked. Though it would seem like common sense. Since you mentioned it, I'll now make sure I really am FAR from anything energetic when drilling. peace
FREAKYDUTCHMEN Posted January 10, 2009 Posted January 10, 2009 You'll need lot's of practice to achieve such kind of effect. You can up the AG to slower the timing of your beraqs. You can also play with pressing theo composition harder or less harder into the hole of the beraq.
Mumbles Posted January 10, 2009 Posted January 10, 2009 Or you could take the easiest and most logical way out and vary the thickness of the walls. Some of the more recent beraq shells I've seen in person were all done by spolette. Very precise, but time consuming. I don't know what kind of Gum arabic percentages slows the burn rate. My experience with gum arabic has always been in solution previously, and that generally requires heat or many days to dissolve. I could have sworn Karl used red gum. I suppose both could work.
swervedriver Posted January 10, 2009 Author Posted January 10, 2009 (edited) Or you could take the easiest and most logical way out and vary the thickness of the walls. Well, I was throwing the idea around of glueing carefully measured and cut 2-3mm id spolettes into the sides of cases, then pushing bound bp slurry into them like Karl describes. Similar to using case thickness as a timer like Mumbles is saying. Using case thickness and drilling is probably easier, a few less steps involved. His doc says RG or GA is used. I'm going to try RG since that's what I have and uses alcohol vs water (such as dextrin, not GA, I think GA is alcohol bound too). I'm guessing water based binders would be a poor choice due to the water affecting the paper cases more. expansion and such, thus unpredictable changes in timing. Edited January 10, 2009 by swervedriver
swervedriver Posted January 11, 2009 Author Posted January 11, 2009 well, so much for that theory, lol. In that case, why not just use dextrin?
FREAKYDUTCHMEN Posted January 11, 2009 Posted January 11, 2009 (edited) The maltese guys use GA. I don't see any problems using it, but it takes lotts and lotts of practice playing with ratio's and burn speed. Disolving GA isn't that hard, just takes al little patience, powdered GA took less than a day to dissolve in cold water. No need to use demi water. I've used a PET bottle, and I've stored 4:1 solution for more than 8 months now. Playing with the wallthickness is also what the maltese guys use for timing, good point there Mumbles. Edited January 11, 2009 by FREAKYDUTCHMEN
Miech Posted January 11, 2009 Posted January 11, 2009 I used meal and red gum, and you can time it rather precise that way. All beraq's went off in about 0.5 seconds, which I consider satisfying for the first attempt. The shell flowerpotted however, so still something to work on. When using this method, punching every beraq exactly the same way is crucial for a consistent delay. I'd prefer sticking a rod in the beraq and then drilling the hole through. For timed clouds or sequential timed beraq's I'd just go with time fuse, taped visco or spolettes (in order of preference). You're never going to get it precise enough with filling a hole with meal and binder.
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