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shell construction time fuse


Merlin

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Well I am progressing slowly. I have perfected my black powder being able to use 1/12th for lift. I use it for lift and burst in 3 inch plastic ball shells. Launched several dummy shells to considerable height and retrieved intact. Loaded the next couple with my BP and falling leaves in the shell as I have not made stars yet. I fired them using 3/4 inch of 1/4 inch time fuse. They exploded about 40 feet give or take into flight. I can only figure my time fuse was too short or the blast from lift blew the lit time fuse into the shell. I used hot melt glue only to the base of the time fuse at the shell entrance. What is the proper way to secure the time fuse so it will not be blown into the shell by the lift blast?

some of the displays I saw on the 4th tonight were incredible making me wonder if I will ever be able to come close. I am committed no matter how long it takes me to this art to make decent shells and then on to rockets. Few spectators realize the work and talent that goes into a good shell burst.

Any suggestions or links you think would help I do appreciate.

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First of gratulations to your good bp. 1/12 at these small shells is really fast powder.

 

For your question. You wan't aoir shells tos blow after 2.5-3 seconds. This means your fuse was way to short.

 

First the easiest thing is to use a fuse burning at about 1 cm per second. Either a visco which got wrappep about 5 to 10 times with masking tape or proper timefuse. (For starting i would recommend too use the visco, as it is the easiest to light fuse).

 

For Visco you take a sample of about 4cm lenght and cover 2.5cm with masking tape. Light it and stop the time, it burns under the tape. If this is around 2.5 to 3 seconds than you got the right timing.

Then use this construction on your shells, if not adjust the covered lenght.

 

After firing skme shells you should adjust the covered area in a mannert, which let your shells break at apogee.

 

If you use time fuse, you've to do the same, but instead of covering with masking tape you just measure the time between your two crossmatch points.

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When you have the time fuse through the hole on the hemi, wrap a fillet of white glued string round the fuse outside the hemi to fill ALL the gaps with glue or string -Yes a 10mm or so fillet of glued string will usually keep the flame out.

 

However; if the shell breaks IN the gun then it's likely that the lift flame has penetrated the shell, if it gets to 40feet than it's likely that there was too little/poor lift or the time fuse worked but was just too short.

 

If you were using visco, remember that it must be wrapped and glued well inside the hemis or the time sector is only the thickness of the hemi case. If the flame escapes from the fuse too early then the shell will break too early/low.

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Sounds good so far. I guess the real question is what speed your fuse burns at? There has been some faster stuff on the market recently burning around 2.2 sec/inch. Even still, that should have been a little over a second and a half of flight time. It would have broken too early, but still up there enough.

 

It sounds like you're still using plastic shells. I'd just rub some PVC cement or something on the outside of the fuse before sliding it into the hole. It should seal quite well. I'm not sure how well hot glue sticks to plastic shells.

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I think mumbles is right: the hot blue is probably having trouble sticking to the shell. I secure my time fuse with a filet (or perhaps a little more) of hot glue on my paper shells, and this seal is reinforced by pasting. I've never had a flowerpot or any problems when using this technique.

 

I would like to do some testing to see if hot glue can affect time fuse.

 

I can vouch for the pasted string around the fuse technique. I use this on inserts to help them withstand the break.

 

 

Here is a question for everyone: what are your experiences with slurry primed time fuse? I got a bit tired of slicing and tying all my time fuses this year, and I had 100% ignition of the few small ground devices I made with slurry primed time fuse. Is this a reliable method?

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I always used hot glue on my plastic hemis. Do the hemis also have the support washer that helps to seals the fuse?

 

I have used the BP slurry method before, but I'm now using NC and BP. The NC seems to soak through the tar coating that I found troublesome before. After I would cut it with a sharp razor it would still want to smear it across the BP core.

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  • 4 months later...

pyrokid I used nc bp slurry on my 2.5" ball shell time fuses this year with no black match and had all of them go off just fine. I will keep doing it like this until I have a failure. I just started building this past December though so I am not very experienced yet.

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I think mumbles is right: the hot blue is probably having trouble sticking to the shell. I secure my time fuse with a filet (or perhaps a little more) of hot glue on my paper shells, and this seal is reinforced by pasting. I've never had a flowerpot or any problems when using this technique.

 

I would like to do some testing to see if hot glue can affect time fuse.

 

I can vouch for the pasted string around the fuse technique. I use this on inserts to help them withstand the break.

 

 

Here is a question for everyone: what are your experiences with slurry primed time fuse? I got a bit tired of slicing and tying all my time fuses this year, and I had 100% ignition of the few small ground devices I made with slurry primed time fuse. Is this a reliable method?

 

Check out some work done in 2007:

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Visco in a 1/4" hole is going to be tough to handle. I cut my time fuse for 4 sec. on 3" shells with 1oz. of powder. I like to put them up there.On 3sec time fuse usually comes out to 2.6 eights per inch.When i insert my fuse i put fuse in, hot glue on inside then outside then glue fuse ring on. If i use visco on 2" i do the same thing, except the fuse sticking out i put 2 turns of masking tape on it to make it light where i want it to.
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