I can give you a few tips on something similar to the bolts. I built a parachute reefing/ line cutter mechanism off of something that Tony A. posted.

http://tqc.yuku.com/reply/32555/2010-Balls-project#reply-32555

Post #27 is a picture of what I have.

It is 1/2" OD aluminum, .062 wall, .375 ID. I threaded both ends for 1/8 NPT and drilled a hole perpendicular to cut the lines needed.

The very first one I built I sealed that sucker up tight. I drilled out my NPT plug, put and e-match in the bore and epoxied it up. I used copious amounts of teflon thread seal tape when installing it. The delrin piston that I was using had 3 o-rings on it to seal.

I used 2 grains 4FFFF in the e-match well and then 5 grains Reloader 25 on top of it. I then used a small patch of cotton ball on top and then the piston.

I tested it. Worked great - until I had to tear it down. The o-rings really didn't slide, the grabbed the sides of the tube and rolled and tore and got chopped horribly. The piston was a single use item and had squished where the o-rings were from hitting the plug stop on the other side. It was also a pain to dig out the epoxy to re-pot the e-match.

The 2nd after I drilled out the e-match I just tied a knot in it and threaded it through with a dab of braces wax and seated it tight. I used just a little bit of thread seal tape. My piston DID NOT have any o-rings. It was 3/8" diameter and slid easily in the tube. I again loaded 2 grains 4FFFF and 5 grains Reloader 25, put the cotton patch on and then the piston. The tie wrap was holding the piston tight against the cotton so there was no free room.

Tested it the 2nd time. Worked perfectly. Cleanup was a breeze this time. Drop the piston out, discard. Pull e-match out, discard and use a q-tip to clean up any wax. Worked exactly the same with 1/4 the prep effort.

I tested it 10 times, and 10 times it worked perfectly. You don't need to seal everything up gas tight for devices like this to work. No need to epoxy seal the wires. Just run them through and use some wax/putty to get a seal.

If you are using 5/8" diameter bolts I'm guessing you'll have at least a 1/4" diameter hole down the middle. I'd really advise then to tap that hole. Once you get your bolts prepped and loaded instead of an epoxy plug, run a piece of nylon all thread all the way through to seal it using a cotton patch to hold it. Turn around time will be consistent. You will have a much more consistent break and no worry of the epoxy strength being different bolt to bolt. And it will be easier to manufacture. Bore a hole out, ream to size, tap. Groove the outside, then finish drilling your lead holes through. No glue, no fuss, no mess and field re-packable in-case a lead wire breaks, loses continuity, etc. You don't have to wait for epoxy to cure. You just have to dump it out, replace the e-match and then put the plug back in.

I don't know how you are holding the plates together, but I'd get the strength of the material of nylon you are using and then figure the minimum area you need to hold them together, then add your factor of safety. From that you can calculate how deep your outside groove needs to be to leave that area in the form of a cylinder between the groove and the inner bore. Also, the groove should probably be a v-groove instead of a nice flat bottomed groove. That way it gives a place to break, though threads are the best stress concentration points around (essentially being one long helical groove)

Anyway, I'm rambling and will stop now.

Edward

Thanks for the input Ed. For my prototype testing this weekend, I was not going to use epoxy at all. I was planning on drilling about a 1/4" hole from the hex head end, drilling down about 2" and tap it for about a 1/4" with 1/4-20 thds. (This is to give greater surface area for the hot glue to adhere to. The groove on the outside is quick and dirty. I chuck the bolt up in my Jacobs chuck on my drill press and then use a thread file to file a groove into the spinning bolt. Once it is un-chucked, I check for thread damage and chase the threads. I will load 4F into the hole, and then insert the ignitor(s), (I may possibly reverse that procedure, depending on how assembly goes). On top of that I will place a ball of recovery wadding, and then seal the assembly with my hot glue gun. My experience has shown that things come apart when they get to move around. Then the damage starts. I believe this is true of ignitors also. Once the ignitors are in the bolt and covered with 4F, where they cannot move, and then the wadding on top of that to insure that there is no movement, I will check continuity. If good, then it gets sealed. Of course, before the bolts are installed in the rocket, the continuity is checked again. I am also believing I will have enough room for two ignitors for redundancy. My O.D. groove will be 3/4" from the bottom of the bolt head so that it should come apart in the middle of the two 3/4" plywood plates/bulkheads. My only concern might be debris jamming something, so the holes the bolts go through should be oversize. Experimentation should prove this out. (Great theory, now we get to prove it.)

For the bolted interface, I would suggest to design it so that the airframe tube of each section is butted up against each other and the nylon bolts just preload that interface. That way, as long as the preload from the bolts isn't exceeded, then the stiffness of the whole airframe will be about the same as if it were an uncut airframe. Stiffness is important because the last thing you want while the rocket is going up is any thrust or aero misalignment. Having the airframe tubes but against each other also will maximize the leverage that the bolts will provide when they resist bending. Are you guys thinking of using in the neighborhood of 8-12 bolts for each joint?

Bear, do you have Q2G2 ignitors for your bolt tests? I have a bunch.

No, Adrian, I do not. I was preparing to order some. If you are coming to the launch Saturday, I would be happy to take some from you. Since we live probably about 70 to 80 miles apart, the only other way to get any is to mail some. I do have some Rocketflite ignitors that I made up, still a little pricey, but they work good and I may go through a bunch of ignitors in running a success/failure test.

This reminds me, any idea of how long I need the tails on the ignitors for the finished product, Steve? 12"

Steve, if you ran some half inch pins through the mating plates, it seems that it might reduce some of the strain that will be put on the bolts, which might help prevent failure. What do you think?

No, Adrian, I do not. I was preparing to order some. If you are coming to the launch Saturday, I would be happy to take some from you. Since we live probably about 70 to 80 miles apart, the only other way to get any is to mail some. I do have some Rocketflite ignitors that I made up, still a little pricey, but they work good and I may go through a bunch of ignitors in running a success/failure test.

This reminds me, any idea of how long I need the tails on the ignitors for the finished product, Steve? 12"

Steve, if you ran some half inch pins through the mating plates, it seems that it might reduce some of the strain that will be put on the bolts, which might help prevent failure. What do you think?

From what James has told me of the Delta III Project Kevin did, they only used 4-6 bolts .. and that was considerably bigger than this. Here's a pic of their early tests. Note they came in form the threaded end .. they corrected that in later tests and the final to come in from the Hex as to avoid hassles w/ the wires.

quote: "The major components will be held together during flight with
these bolts. The bolts are drilled and each packed with 1 gram
of black powder, then filled the rest of the way with epoxy.
The on-board electronics will fire the charges,
allowing the sections to separate. Here you can see a before
and after picture of a bolt."

Bear .. 12" seems a little short, depending on where the electronics are located. The 'pins' seem like a good idea to provide additional horizontal stability .. I hope to get all the motor/bulkhead assemblies built this weekend and will have a better idea of how it will all fit together.

Here are, more or less, the 3 Proton Stages.

will extend the 3rd stage a little.

Booster is 60", stage 2 is 48" and stage 3 is around 72". I plan to add fin and motor mounts to the 3rd stage for a potential 3 stage flight at some point. The critical issue of course will be getting the CP/CG right on all scenarios .. may be quite difficult. But I figured since we'll be breaking it apart for recovery anyway .. why not.. plus the Motor Mount/Fin assembly will add some needed weight to the upper section.

What size bolts did they use? The picture looks like a 3/8 X4". I was thinking of something at least 2" long, 1 1/2' for two pieces of 3/4" plywood and a 1/2" for the nut. Easy to get longer, and/ or to start long and cut it down to any length we want. I can get 3/8' bolts all day long, but 1/2" and 5/8" are more difficult.

Steve, I presume the dimensions in your drawing are meters?

Steve, I presume the dimensions in your drawing are meters?

yea .. that's the original drawing we started with. We will vary slightly but close to that.

Still waiting for Kevin to get back with details .. but it may be 3/8" .. feel free to pursue that. However I'm not going to spend any time reinventing the wheel when they have a flight tested and proven technique on an even larger and more complex rocket.

A more important design issue is the booster/outboard attachment detail and nosecone design. btw, Rich has recalculated all the dimensions into inches and the boosters will be 44" long and the nosecones 12" long. Our scale is 12.9.

There is not a lot of wheel to invent here. The photos and the description almost says it all. Just need to know which size to work with so we can figure out the stress tolerances. When you think about it, all there is, is to drill a hole, put powder in, add a crusty wire, and seal it so the stuff does not fall out. The question is, will it support and exceed the stress that will be placed on it. Reduce the stress, and the less number of fasteners that are necessary. Have I missed something?

There is not a lot of wheel to invent here. The photos and the description almost says it all. Just need to know which size to work with so we can figure out the stress tolerances. When you think about it, all there is, is to drill a hole, put powder in, add a crusty wire, and seal it so the stuff does not fall out. The question is, will it support and exceed the stress that will be placed on it. Reduce the stress, and the less number of fasteners that are necessary. Have I missed something?

Just size of bolt, size of hole, depth of hole, amount of BP, type of ematch, seal material, number of bolts, to score or not score the outside (don't think he did), torque on bolts, thickness of bulkheads .. all worked out by them already. You're results will likely be fine, but I am more comfortable going with his "flight tested, flight proven" technique. Like I said, go ahead if you wish but it seems a waste of ematches and bolts ($$$), and I'm going with Kevin's design in the end anyway. We'll go through enough ematches and bolts as it is later on testing our assembly.

Your call. I see it as a different rocket, different weights, different aerodynamically induced stresses, different number of bolts, different configurations, new wheel. Where do you start? You can make everything identical to Kevin's and still have to make it different. Again, your call. I have enough other things to keep me busy until you have it figured out and we start on prototyping and manufacturing. I look forward to seeing more details of Kevin's so we can reproduce them to see how well they meet the needs.

Great project. Fun to read. A long time ago I made these pyro-bolts:

The brass part has an undercut. The stainless bolts are just igniter holders. The advantage of the brass is that they are relatively strong before breaking. Here is a drawing (sorry... metric):

More info here: http://www.nerorockets.org/nero/neh-projects-e36-para.htm

Jeroen

That is very interesting and gives insight. Thank you for sharing this with us.

I would like to express the same with Edward in regards to his sharing his line cutter also.

That is very interesting and gives insight. Thank you for sharing this with us. I would like to express the same with Edward in regards to his sharing his line cutter also.

There is a line cutter on that link as well. Make sure you test well if you decide to use kevlar. It would bind up our cutters.