Rivet all the things...?

[ActingLikeAKid]

So I'm re-thinking my Mega Vector Force project and had a question ...


I have two transitions in this rocket - the first is right above the split, going from 54 to 38. The second goes from 38 to 29.
There have to be rivets in the upper transition as the nosecone and top body tube cover the electronics. I know I brought up making the 38mm section removable so that I could later put an av-bay in there (and potentially even a chute). My big question: Do I rivet the upper and lower sections of the 38mm tube, or just the upper?

Riveting both gives me more flexibility (in terms of what I can do with that later) but also gives me more flexibility (in terms of a rocket that flops around a bit more).
Epoxying one end gives me a stiffer rocket but may limit future modifications.

I'm thinking I'll keep it the way it was - rivets on both sides of the upper transition (my logic being that, in the event of a hard landing, there's a longer lever to apply force to the lower rivets, if that makes sense).

Open to suggestion on this.

 

[NateLowrie]

So I'm re-thinking my Mega Vector Force project and had a question ...
View attachment 320188

I have two transitions in this rocket - the first is right above the split, going from 54 to 38. The second goes from 38 to 29.
There have to be rivets in the upper transition as the nosecone and top body tube cover the electronics. I know I brought up making the 38mm section removable so that I could later put an av-bay in there (and potentially even a chute). My big question: Do I rivet the upper and lower sections of the 38mm tube, or just the upper?

Riveting both gives me more flexibility (in terms of what I can do with that later) but also gives me more flexibility (in terms of a rocket that flops around a bit more).
Epoxying one end gives me a stiffer rocket but may limit future modifications.

I'm thinking I'll keep it the way it was - rivets on both sides of the upper transition (my logic being that, in the event of a hard landing, there's a longer lever to apply force to the lower rivets, if that makes sense).

Open to suggestion on this.

If you haven't printed the transitions yet, consider using 4-40 button head cap screws. Adjust the print to include some hexagonal holes for a 4-40 nut. It mounts cleaner that the rivet and won't wiggle and much. The button head is also smaller than the comparable rivet head.

As to you suggestion of glue or fasten, having built many rockets now I always try to fastener when I can. The extra flexibility you have is worth it especially if one of the parts breaks (as you can salvage the other intact if it fastened and not glued).

 

[ActingLikeAKid]

Good call on the salvagability, thanks! And after the disatrous attempt with 3d printing, I'm doing "coupler transitions" ... two couplers joined with centering rings.

Something like this:

So this is the 29->38 transition. "A" is a 38mm coupler, 40mm long. "C" is a 29mm coupler, 114mm long. "B" is a 3d printed shroud that slides over C. Two centering rings sit between A and C so that the 3d printed part bears no load. In fact, I could remove it and the rocket would fly, but would be draggy. And the length of C is 40mm in the lower tube, 30mm in the upper tube, 44mm of transition length.

I like the idea of "wells" for nuts; I was considering doing something like that with the BlueTube - basically gluing a nut to a washer, then gluing the washer to the inside of the inner tube. But then I realized that it would be an enormous pain to get everything lined up perfectly and rivets seem to be the standard.

 

[rharshberger]

If you haven't printed the transitions yet, consider using 4-40 button head cap screws. Adjust the print to include some hexagonal holes for a 4-40 nut. It mounts cleaner that the rivet and won't wiggle and much. The button head is also smaller than the comparable rivet head.

As to you suggestion of glue or fasten, having built many rockets now I always try to fastener when I can. The extra flexibility you have is worth it especially if one of the parts breaks (as you can salvage the other intact if it fastened and not glued).

+1 using button head screws instead of rivets, they are easy to remove and they allow less wiggle due to the fact they clamp the tube between coupler and airframe. Yes they are a bit more work to install in non-FG/CF airframes but worth it.

 

[ActingLikeAKid]

+1 using button head screws instead of rivets, they are easy to remove and they allow less wiggle due to the fact they clamp the tube between coupler and airframe. Yes they are a bit more work to install in non-FG/CF airframes but worth it.

Are you talking about self-tapping screws, or somehow affixing nuts to the inside and then screwing into the nuts?

 

[rharshberger]

Are you talking about self-tapping screws, or somehow affixing nuts to the inside and then screwing into the nuts?

Actual button head machine screws, not self tapping, they will require either a regular nut or tee-nut on the backside but they are well worth the effort. I don't like the allen types in smaller screws like #2 thru #6 as wrench is so small that the slightest bind and the allen socket strips, but phillips button head screws work great.

 

[Nytrunner]

All of the things!

Something I like to due with lo/mid power paper tubes is to drill the outer tube a size smaller so that the rivet forces it into the inner hole, then the expanding portion inside (if you use the right size rivet) grabs squeezes it back in. Haven't had slop movement yet.

But then again I really like rivets, and (as always) your altitude may vary.

 

[ActingLikeAKid]

Actual button head machine screws, not self tapping, they will require either a regular nut or tee-nut on the backside but they are well worth the effort. I don't like the allen types in smaller screws like #2 thru #6 as wrench is so small that the slightest bind and the allen socket strips, but phillips button head screws work great.

It's looking like PEM nuts and machine screws ought to be the answer. 4-40 or 6-32...probably #6 because I already have #6 holes in the top section...

 

[rharshberger]

It's looking like PEM nuts and machine screws ought to be the answer. 4-40 or 6-32...probably #6 because I already have #6 holes in the top section...

PEM nuts are an option for sure, many here on TRF use them.

 

[NateLowrie]

It's looking like PEM nuts and machine screws ought to be the answer. 4-40 or 6-32...probably #6 because I already have #6 holes in the top section...

#6 will work but be overkill.
#4 is still overkill, but the lowest I'll use because #2 is a pain in the butt.

If you already got the holes though 6 shouldn't be a problem. If you are having trouble sourcing the nuts and screws, let me know. I have #4, #6, #8, and #10.

 

[Banzai88]

Missile Works and McMaster-Carr both have PEM nuts available. I usually just order a complete set of hardware with drill bits for the PEM nuts and screws all in one.

 

[ActingLikeAKid]

Missile Works and McMaster-Carr both have PEM nuts available. I usually just order a complete set of hardware with drill bits for the PEM nuts and screws all in one.

Thanks! Ordering from McMaster today. Added the PEM nuts to the cart, looking at 4-40 screws....
"Oh, those come in titanium? SWEET. That would be cool. I mean, the weight savings would be pretty much nothing but... I wonder how much they are? $4.60? AWESOME. I can handle that. Is that for a bag of 25?...

...Oh. That's per bolt. *ahem* NEVER MIND"

 

[Banzai88]

Yeah, just make sure that if you're going stainless throughout that you use some antizieze to prevent galling. I typically use #4 and #6 PEM nuts. Be sure to double check the material thickness of your tubes. Wouldn't do to have a PEM nuts that has a .060 shoulder in a .030 tube. Shorter is ok (to a point), longer is not. If you're so inclined, McMaster lists the installation hole size. Spend the $3 and get the perfect drill bit, too.

Typical Philips head button head screws have a high profile and you'll be tempted to go with hex heads....be aware that without a sharp, fresh allen wrench, any excess torque on stainless button head fasteners tends to strip the hex out of the head. Ask me how I know!

 

[ActingLikeAKid]

Yeah, just make sure that if you're going stainless throughout that you use some antizieze to prevent galling

I was thinking of using loc-tite to stop them from backing out during flight. I don't anticipate that being an issue but I'd rather be wrong... Since the loctite is liquid until it cures, would that work to prevent galling, you think?

. I typically use #4 and #6 PEM nuts. Be sure to double check the material thickness of your tubes. Wouldn't do to have a PEM nuts that has a .060 shoulder in a .030 tube. Shorter is ok (to a point), longer is not. If you're so inclined, McMaster lists the installation hole size. Spend the $3 and get the perfect drill bit, too.

Yep. BlueTube is 0.062, min thickness is 0.062. Should be perfect. Drill bit is only $2, score!

Typical Philips head button head screws have a high profile and you'll be tempted to go with hex heads....be aware that without a sharp, fresh allen wrench, any excess torque on stainless button head fasteners tends to strip the hex out of the head. Ask me how I know!

Ewww... Yeah, I'm not chasing speed or altitude with this. I mean, I'd like to get over 5280', but I also want a rocket that's easy to work with. And I *always* have a screwdriver around. The right size allen wrench? Not so much.

 

[ActingLikeAKid]

Order placed with McMaster. I may have dropped an extra $20 on PVC pipe and fittings. No, I'm not doing plumbing work, and I don't need another rocket stand. But EVERY TIME I use my PVC rocket stand, the kids want to take it apart and play with it. I figure I'll get a bunch of fittings and a couple of half-inch pipes, chopped up into 6 to 12" pieces, and they can go to town.