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Payload bay nosecone positive retention methods

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bobbyg23

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So assume that I want to use threaded inserts. What am I looking for? I've not used threaded inserts before. If I was going to use a bolt I'd be looking for something like a 4-40 to be the right size. How do I find the right threaded inserts for those?
No threaded inserts needed. Just use screws into the nosecone.
 

Joshua F Thomas

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I also want this setup to be compatible with 4-40 nylon sheer pins, for when I use dual-deploy.
 

Nytrunner

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I also want this setup to be compatible with 4-40 nylon sheer pins, for when I use dual-deploy.
4-40 shear pins would be overkill. 45-50 lb breaking strength meaning you need larger ejection charges in a very small tube.
Can you find 2-56 inserts? 2-56 are more suited to that size (25-30lb break)
 

Joshua F Thomas

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I was actually thinking along those same lines, and I have 2-56 sheer pins already. Tiny inserts seem to be harder to come by, but I'll keep looking.
 

Joshua F Thomas

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That makes sense. If you have a hobby shop locally, they should have threaded inserts in 4-40. Better yet, just get a 4-40 tap and just make threads in the nosecone.
I'm concerned about the plastic deforming. The threaded inserts I can either heat-fit or use epoxy to hold in place.
 

Joshua F Thomas

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Looks like McMaster-Carr has what I need.

 

Joshua F Thomas

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That makes sense. If you have a hobby shop locally, they should have threaded inserts in 4-40. Better yet, just get a 4-40 tap and just make threads in the nosecone.
As I said before.... "I'm concerned about the plastic deforming. The threaded inserts I can either heat-fit or use epoxy to hold in place."
 

Nytrunner

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Solid plastic cone won't deform on you. The forces here just arent significant enough for that.

Thin estes nosecone plastic, sure that'll deform
 

TheTank

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2-56 shear pin straight into the nose cone. Tap the hole, just drill a little deeper than the thread length. No need for an insert. It will hold.

On smaller cardboard DD rockets im using one 2-56 pin on the cone just to prevent an early deployment from the shock of the drogue charge and shock cord extension. I harden the area around the hole in the cardboard with thin CA to create a hard shearing surface. Its all that is needed i have found and if I didnt have the second charge, the cone would stay on no problem.
 
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JoePfeiffer

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You don't want to use threaded inserts with shear pins -- the sheared section of the pin would stay in the insert, and be nearly impossible to remove. On my 2.2" fiberglass and 2.6" cardboard airframes, I use two 0-80 shear pins; on the cardboard rockets I try to stiffen up the area a little with CA. Other people put some brass sheet metal at the holes, but I haven't found that to be necessary.

Also, you aren't going to epoxy anything to a urethane nose cone -- it won't adhere. If you use thread inserts, you'll want these:
You *really* want the little "neck" at the bottom of the insert. You size your hole so the first ridge of the neck sits at the top of it, and then heat with a soldering iron to set it. I got some once that didn't have it (oh, so *that's* why the price was so much better!), and trying to get them straight was nearly impossible. Get the longest ones that you've got room for; the longer the better. They sell special soldering iron tips to install them with, but I haven't found that to be necessary. Standard soldering iron tip works just fine.

But frankly the people saying you don't need them here are right. Self tapping #4 screws are ideal for this application. I'd probably use them anyway because I think they give a nice, professional look, but I'd realize I was just satisfying my own preferences.
 

Alan R

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why not just use a screw thread on NC and tube? very similar to the twist-loc mentioned before.
make a receiver thread inside the payload bay. Would have to be inset enough to allow the NC shoulder to go in, then 'catch' a matching screw on the base of NC, but not required to be any exact distance. Screw thread could just be epoxied to any existing nose cone. Even just one turn would be enough to work.
I have a payload bay currently that I could play with this idea.
 

Rocks&Rockets

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Chop the useless attachment eye off your plastic NC. Fit in a 3/8" cedar block attached with 3 screws and some gorilla glue. Close it up with a stepped bulkhead tied to the cedar with a piece of threaded rod.
 

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Banzai88

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Chop the useless attachment eye off your plastic NC. Fit in a 3/8" cedar block attached with 3 screws and some gorilla glue. Close it up with a stepped bulkhead tied to the cedar with a piece of threaded rod.
The Always Ready Rocketry kit that the OP has uses a solid urethane nose cone, thus his dilemma.
 

Joshua F Thomas

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You don't want to use threaded inserts with shear pins -- the sheared section of the pin would stay in the insert, and be nearly impossible to remove.
Ah dang, that's a good thought. This is why I like to ask people before doing things!
 

Joshua F Thomas

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But frankly the people saying you don't need them here are right. Self tapping #4 screws are ideal for this application. I'd probably use them anyway because I think they give a nice, professional look, but I'd realize I was just satisfying my own preferences.

Thanks for the info, much appreciated. How am I going to sheer pin to dual deploy this then? Hurm.
 

Joshua F Thomas

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I guess I could have this come down in three pieces, with the ebay held to the body at both ends with sheer pins. Primary charge pops the ebay+frontbody+nosecone off as one piece and deploys the drogue. Second charge pops the frontbody+nosecone off the ebay and deploys the main chute. Nosecone stays secured to frontbody via self-taping screws or whatever else, doesn't matter much at that point.
 

Nytrunner

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Thanks for the info, much appreciated. How am I going to sheer pin to dual deploy this then? Hurm.
If it's a solid cone, drill a clearance hole for the 2-56 threads (hole juuuust large enough so the threads don't engage)
That way when the pins shear, the butt ends will just drop out
 

JoePfeiffer

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Somehow I missed that your positive retention and shear pin questions were for the same place! I'd put a hole completely through the body tube and nose cone shoulder. Interference fit in the body tube (and I'd try to thread it); slight clearance through the nose cone shoulder. Install before flight, push the stubs through the shoulder after flight.
Take a look at the force required to shear the pins, and the pressure you need to get that force, to decide the size and number you need.
I don't like ejecting the body tube with the parachute, though I've seen it done successfully. It relies on inertia to eventually pull the chute out of the tube -- I like a more positive ejection, which is what you get when you eject the nose cone.
 
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Alan R

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proof of concept prototype. the interior ring receiver gets epoxied in at the right depth, allows you to twist the nc on tight. Pic is just for show, actual will be glued much deeper into the tube.
This is standard NC with a shock attachment. The cross bars have screw holes that I would use to attach my tracker. Add screws before glue.
If you're going with a hollow NC, add a glue shoulder to the print that goes up inside the nc and allows the thread to fit flush with the base.
I'm just following along and don't know much, just trying to keep my nose cone attached to my bay. This seemed like it would work.
First draft 3d printed today.
IMG_0468.jpg
 

gtg738w

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For now, I’d tap the nose cone 2-56 and use steel screws. I’ve used that BT-20 to 4”. I wouldn’t worry about deformed threads or inserts. When you’re ready for dual deploy just drill out the inner holes to be a generous clearance fit and switch to nylon screws.
 

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