Glueless nose cone - very cool, but................

So one of the build techniques I used when I built my 3" Darkstar was Crazy Jim's "glueless nose cone". This is a very cool way to do FW cones, and as always, Jim contributes SO much to us all here, and in the hobby in general. It's brilliant and simple - one of those things that makes you say to yourself, "why didn't I think of that?" Jim tends to put me in that place often it seems.

However, today I found a little problem with this particular technique. I was doing some ground testing, and at one point it seemed like I just could NOT get my shear pin holes to line up. They were just the teensiest bit out of alignment, and it was really frustrating. I swore a bit, gnashed my teeth, managed to get two pins in finally, and proceeded with the test. The charge in the first test was a bit weak, so I decided to up the BP and try again. This time the holes were even more out of alignment! Huh?? What's going on here? .

You may have guessed the problem. Here's the thing. The nose cone shoulder is not glued in, but merely wedged in tight. But not quite tight enough it turns out. See, when I tighten the nut holding the bulkhead in place, this is what keeps the whole assembly together. But it's possible to tighten it just a bit more, and in doing so the shoulder is pushed just a slight bit more into the cone. And that little bit is enough to make the shear pin holes lose their alignment. Dang.

Not quite sure how I'll rectify the situation, but I'll figure something out.

I think I'll glue that shoulder in after all,
s6

Three screws equally spaced around the nose cone. You screw the nose cone to the coupler. I would guess 4-40 or 6-32 would be sufficient. Tap right through the cone and coupler. Only do one at a time and install a screw in each new hole as you go. In the attached picture, you can see one of the screws and one of the tapped holes.

I cut a short length off of the shoulder piece and epoxy it into the cone. This gives the glue-less shoulder a positive stop, and the holes always line up.

If you don't have a ring on the coupler to butt up against the nosecone then you will get movement with charge pressure. If you don't want to put a ring on the coupler, you can glue a ring inside the cone that mates with the fore of the coupler and restrict movement that way.

I've run into this too. What I do is drill the holes for the shear pins ever so slightly too big, and just shove them in rather then screw them in. Makes for a bit of wiggle room.


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