Ideas for making a transition?

[ActingLikeAKid]

I'm rebuilding my upscale Vector Force after its untimely 120+mph meeting with the ground. I was able to salvage the fincan and the motor mount; just need to put a new top on it. Instead of going 54->38->29 on the airframe, I'm, uh, calling it less of an "upscale" and more of an "interpretation" and changing the upper part of the rocket to a single 38mm section. (Unless I get entirely tired and frustrated at this process and just make it a long 54mm diameter airframe).

Based on what worked last time, I think I have a pretty good starting point for the transition:

More detail on this: Lower airframe is 54. Upper airframe is 38. Going to use a piece of 54 coupler as a shoulder to slide into the lower airframe, and a bulkplate with eyebolt at the bottom. Two CRs hold the upper airframe inside the coupler. A small section of 54mm airframe glued to the top of the coupler acts as a sort of thrust ring to transfer the load to the upper section. The only thing I'd need to do would be build a hollow cone (marked "HELP!" in the image) that smoothly takes me from 54mm to 38mm. I have a friend who's helped me in the past with 3d printed bits but I don't want to bug him again (besides, he'd have to ship them, too). John Coker has an excellent video on his site on how to build a transition using foam and a hot-wire cutter; the problem with this is that the "grain" of foam might be coarse for this application (I think he was going from about 7 inch tubing to 3 inch) and also I don't have (nor do I have the time or inclination to make) a hot wire cutter. With the 54mm section of airframe, this won't be a load-bearing piece, it will just be for aerodynamics.
So far, ideas I've had include:
-Taking a (soft, maybe pine) wood block, cutting a hole in it, then using a belt sander to slowly, progressively grind it into about the right shape.
-wrapping it in layers of masking tape (using overlaps to get the change in diameter) which seems tedious, but I know how quickly I've made a thrust ring on a 29mm motor (e.g. to fly a BP motor in a PSII rocket without a motor block).
-Using layers of construction paper to do essentially the same thing, but sort of like papier-mache.
-Using foam and just sanding it to shape. I don't have a lathe, but I figure that with something this small, "just being patient" might be sufficient.

I'd probably glass over any of these options for strength and smoothness.

Open to creative and time-saving ideas.

 

[rstaff3]

Ordinary cardstock with a layer of fiberglass would work. 1/64" fiberglass or ply would work too. All these use good old modroc techniques. You could probably figure a way to backfill with 2-part foam.

 

[ActingLikeAKid]

Ordinary cardstock with a layer of fiberglass would work. 1/64" fiberglass or ply would work too. All these use good old modroc techniques. You could probably figure a way to backfill with 2-part foam.

Thanks! I hadn't even thought of leaving it "empty", but that makes sense

 

[prfesser]

I've made transitions from kraft paper---virgin kraft is strongest if you can get it---and epoxy, adequate for at least the lower end of high-power. Make four or five paper transitions, coat each with epoxy, press them together with some weight (not so tightly that they crumple) until the epoxy cures. Sand ends flat.

Best,
Terry

 

[ActingLikeAKid]

Great suggestions. I'm thinking I'll make the transition out of cardstock, paint the cardstock with epoxy, then put on a layer of glass (with enough overlap at both ends to stick). Thanks all!

 

[Woody's Workshop]

Since it appears that it doesn't separate at this point, why not just use epoxy putty and mold/sand one in place?
Or would that be adding too much weight? It would add to stability I would assume.

 

[Bat-mite]

Use a plastic Nike Smoke nose cone and cut it at the 38mm and 54mm parts of the taper. Inside, use the ring piece of a 54mm > 38mm Aeropack adapter.

 

[ascastil]

I've made transitions from kraft paper---virgin kraft is strongest if you can get it---and epoxy, adequate for at least the lower end of high-power. Make four or five paper transitions, coat each with epoxy, press them together with some weight (not so tightly that they crumple) until the epoxy cures. Sand ends flat.

Best,
Terry

Out of curiosity, are saying to coat with epoxy while flat? Will it not flex into a circular shape after it cures?

Edit: Tried to delete post because it seemed like a silly question. Its probably already formed I would guess?

 

[ActingLikeAKid]

Use a plastic Nike Smoke nose cone and cut it at the 38mm and 54mm parts of the taper. Inside, use the ring piece of a 54mm > 38mm Aeropack adapter.

...And this is why I post stuff like this.
Though it struck me that:
1. Anyone with an NS nosecone wouldn't want to chop it up
2. I'd probably pay more than I wanted for it.
3. I'd be sad about destroying an NS nosecone just for a transition.

BUT...

Really all I need is a tapered plastic tube. You know, like a funnel....

 

[Bat-mite]

Awesome. Just find one that has the right taper and the right measurements.

 

[ActingLikeAKid]

Awesome. Just find one that has the right taper and the right measurements.

That should be a fun conversation in AutoZone. "Can I help you, sir?" "Uh, no, just measuring these funnels with a pair of calipers, I'm fine.."

 

[rstaff3]

I bet get the plastic cut and sanded properly would be a lot more work than cardstock and epoxy.

 

[MikeyDSlagle]

Use OR to print out a transition, either paper or cardstock. Shape it and put in a 38mm tube. Use a coupler if you want it to break there or the actual bodytube if you want the transition firmly attached to the 38mm bodytube.
Stand it up level and use a tube to hold the transition piece level. Have a 54mm coupler or body tube ready and centering rings to fit inside that coupler and around the 38mm tube. Or have centering rings already glued into the tube. Extra holes in the CRs will let foam move up through the coupler as well.
Fill transition with foam then slide the 54mm tube down onto it. Let the foam do its thing. It actually soaks through printer paper and gives it a nice slick finish. Or fill with epoxy.
The rings will be glued to the 38mm tube and 54mm tube so it will be secure.
I've done it using smaller tubes and I used bodytubes rather than couplers. That would probably give a cleaner look. It works pretty good and you likely have all you need one hand.
Or use a funnel.

 

[prfesser]

Out of curiosity, are saying to coat with epoxy while flat? Will it not flex into a circular shape after it cures?

Edit: Tried to delete post because it seemed like a silly question. Its probably already formed I would guess?

Yes, it's already formed. Kraft paper is rather stronger, thickness for thickness, than most other paper/cardboard. It's why pyrotechnicians have been using it for motor casings for quite some time.

Best -- Terry

 

[rstaff3]

Here is probably more than you ever wanted to know about cardstock. https://www.papermodelers.com/forum/tips-techniques/3280-cardstock-property-tables-terms.html

From a guy who should know.



These are all big a$$ stomp rockets.

Photo via Mike Bauer.

 

[JohnCoker]

I put together a video on making one out of foam with plywood gussets:

[video=youtube_share;5mUKQ7CUd8I]https://youtu.be/5mUKQ7CUd8I[/video]

 

[OverTheTop]

Have you thought about 3D printing it? Non-structural so should be pretty easy, if you know somebody with access to a printer.

Here is an example of my Nike Apache. This is 3"-4", and structural so it is quite chunky. Material is ABS.

 

[ActingLikeAKid]

I put together a video on making one out of foam with plywood gussets:

[video=youtube_share;5mUKQ7CUd8I]https://youtu.be/5mUKQ7CUd8I[/video]

As always, your videos are great and the results gorgeous.... But since I'm working with a relatively small transition (54 to 38) the foam technique seemed a bit overkill. And I don't have a lathe or a hot wire cutter, both of which seem like they'd be really handy in making this come out as well as yours. Thanks for sharing these videos, though - they're incredibly helpful!

 

[Maxitout]

I've made a couple of transitions like this. What I've done, is make about 4-6 small "fins" to go into the coupler, and make the outline shape for the conical transition. Then, I use 2-part foam, and fill each one up, one at a time. Then, trim the excess down with sandpaper, dremel, etc. Open Rocket should let you print out a template for this, then cut out a piece of fiberglass cloth, and epoxy it around the foam. Then, sand, prime, fill etc., till it looks good.

Phil L.

 

[Evilash]

Have you thought about 3D printing it? Non-structural so should be pretty easy, if you know somebody with access to a printer.

Here is an example of my Nike Apache. This is 3"-4", and structural so it is quite chunky. Material is ABS.
View attachment 326644 View attachment 326645

3D printing is a great way to do this. I made an interstage coupler that way, in PLA believe it or not, and it works great. It has bulkplates and protection around the places where heat would be applied and those sections are coated with JBweld. You can set the fill rates and wall thicknesses when you order the print.

3D hubs is an awesome way to get it printed locally and at a reasonable price. Tinkercad is free and you can use that to design it. The interstage is 3 peices that all go together, this is 4" to 2.6"