Preferred cardstock/cardboard tube scratchbuilding method?

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Jun 10, 2023
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I'm in the middle of making an AXM Paper Space Scale Models Delta IV Heavy 1/96 cardstock model, and, funny enough, I'm having some difficulty with the seemingly simple task of crafting cylindrical tubes cleanly. This surprised me, as I've accumulated a fair bit of experience making cardstock/papercraft scale aircraft gliders, though apparently those are more visually forgiving, I guess because the aircraft models I'm making are at a small scale, and the seam is typically on the belly. Here at least some of the seams will be covered by conduit details when the model is complete. Still, I'd like to be able to make a nice smooth cylinder.
d4h - 4.jpeg

Non-ideal issues that I'm running into include:
  • Not having an exact-diameter mandrel to work with (this is just a mailing tube I happened to have)d4h - 7.jpeg
  • Cardstock buckling and leaving unsightly creases when curling it into a tube (this is way more obvious in person)d4h - 5.jpeg
  • The seam bumping out compared to the cylindrical profiled4h - 8.jpeg
  • The seam joiner underneath being evident through to the outsided4h - 6.jpeg
I've been trying to address these issues by:
  • Curling the cardstock around larger tubes first
  • Giving up on trying to over-curl the cardstock so that it springs back to the desired diameter
  • Attempting to pre-over-curl the cardstock adjacent to the seam
  • Pressing the seam against a slightly undersized mandrel tube while the glue is still wet, to shape the joiner
  • Putting light rubber bands around the tube as it dries, in an attempt to squeeze any projecting areas inward, hoop stress-styled4h - 1.jpeg
  • Adding bulkhead formers ("centering rings," but just discs), made out of double-layered cardboard, insided4h - 2.jpeg
So far, it's not enough. Are there any tips and techniques anyone can recommend?
  • Make the seam joiners out of thinner paper than the cardstock? Seems like then the seam would form a ridge, due to the cardstock wanting to return to flat.
  • Use lots of closely-spaced bulkhead formers? Dunno, cutting circles out of thick material accurately is tedious, and I don't really want to use wood etc....
  • Build up a smaller existing tube into a correct-sized mandrel—how would one best do that without introducing its own seam?
  • Anything else?
Or is there not much improvement to be had here, such that it would be better to make a structural tube, i.e. in the style of a typical model rocket body tube, and then use printed cardstock or paper just as an aesthetic wrap? I'm interested in scratchbuilding some paper body tubes regardless. What's a good method?
  • Convolute, i.e. simply rolled, as GlenP for example has done? There's the matter of the seam. Could one try to build up layers in which each layer is the exact circumference, so that there's a butt joint seam but no bump? Rather than simply glue it, has anyone tried the technique of applying glue to the paper while flat, letting it dry, and then ironing it to make the bond once it's rolled in place?
  • Spiral-wound, as prfesser for example has done? For strength and surface consistency I guess it would take at least three layers, so that each spiral seam has two other layers bridging the seam. Then there's the question of whether to find appropriate pre-gummed kraft paper or to apply glue to kraft paper strips by hand. This excellent Instructable indicates that it's good to wind each spiral in the same direction, so that adding a layer doesn't loosen the one underneath. By the way, if you want to see even Tim Van Milligan struggle to spiral-wind a tube by hand, here's the Apogee page on it. :)
  • Hybrid convolute and spiral-wound, as on the Estes Tech-Pak kit (see step 3 of the instructions PDF), which kuririn and Chris Michielssen (Odd'l Rockets) have tried? In this method, there's a thin inner paper layer wrapped around the mandrel (convolute), and then spiral-wound layers added. There is a small internal seam from the inner layer, though I suppose if it's thin enough, it won't show on the outside. The Tech-Pak kit has you winding the spirals in alternating directions, though one wouldn't have to follow that.
  • Something else?
All prospective methods require a correct-sized mandrel for the inside diameter, yea?

By the way, I've been using Aleene's Tacky Glue pretty much exclusively. Because I'm building healthy, I'm trying to keep to PVA glues like that. Even glue sticks are out.

Nose cones I've been doing better at than tubes. They may be more forgiving because the curvature changes, rather than being a constant-radius cylinder, so unevenness isn't as noticeable. On this model I made the effort of printing an extra sheet of nose cone parts and cutting them into separate internal joiner strips, which was totally worth it to turn the seams into butt joints. I thought that I could cut just inside the printed lines and get rid of the dark seam lines, but no luck on threading that needle so far. Also, while the glue is still wet, it helped to burnish the seams from the inside using a large-diameter ball-ended stylus against the craft mat—it really knocks down the seams.
d4h - 3.jpeg
d4h - 9.jpeg

By the way, if you get real fancy and gently burnish the seams and some of the neighboring surface inside the nose cone against a slightly softer (but not too soft) rubber mat, you can even round the surfaces a bit, approximating complex curvature (ooooooh).

I put this thread here rather than in Techniques because I'm looking for recommendations particular to cardstock construction methods. Though this model will be static, the techniques discussed are of course applicable to flying models.
Good morning, and you're right, it's hard to get those seams to line up perfectly. I've always "dragged" the cardstock hard over the edge of my desk, several times to give it a decent curl. The edge you hold will still be mostly flat, so turn the cardstock around each time so that both edges to be glued get that curl. Then if possible I curl the cardstock tightly by hand and insert it into a much-smaller tube, leave it long enough to take a set.

I've made mandrels of a specific size by spiral-winding additional gummed tape around a smaller mandrel, then filling and sanding as for a body tube. It's a lot of work, mainly if a number of tubes of the same size are needed.

I tried using a strip of gummed tape as a seam joiner. Failure; the wetted tape ripples a bit as it dries. Maybe use one of the less-tacky masking tapes, blue tape or Frog tape? That would avoid excess glue being squeezed out, and it might be possible to reposition without tearing the cardstock (much).

Hope this helps!
The AXM designer has a YouTube channel, so maybe some of his techniques for avoiding creases. Another option would be to scale print the AXM model to available body tube sizes and print on thinner cardstock like 65lb or a high quality 24lb bond to function just as a wrap.

The AXM models are really nice.
Thanks for the thoughtful comments, @prfesser and @NOLA_BAR! I didn't know AXM had a YouTube channel, checking that out now. (Volume alert on the intros of some of the videos!)

I'll give those techniques a try. Interesting idea on tape as a seam joiner. I'm so acculturated to using glue, it's easy to forget about tape! Could also use double-stick tape, the high-tack permanent stuff, on a cardstock strip as a joiner—then it wouldn't be as susceptible to turning into a "tent fold" as it would be using regular tape alone.

Good point about making sure a built-up mandrel has a smooth surface, important also for being able to slide a finished spiral-wound tube off. Given that water-based glue of course shrinks as it dries, the Instructable recommends sliding the tube off the mandrel before the glue is fully dry. Though maybe with waxed paper over the mandrel, held in place with thin foil tape or the like, it would be feasible to slide the tube off after drying.

One more cardstock curling technique I've been trying out that I forgot to mention above is to take a slightly damp sponge, use it to moisten the backside of the cardstock, wrap the cardstock around a mandrel, and rubber band it in place until it dries out. This method showed some promise. Think I just need some more practice with how wet the sponge should be, depending upon the cardstock thickness.
The 1/96 NROL 82 Delta IV Heavy static model is now complete, at 30" tall with 2" diameter tubes. For details on the rest of the build, see the thread over on the Paper Modelers forum. A note on potential conversion for flight: as-built the model weighs 87 g.
D4H - 21.jpg

A fun tidbit is that the orange insulation on the hydrogen tank sections is made from cardstock textured with fine parallel ridges (Bazzill Fourz Tangelo), which makes it look like the real surface. It also saves a lot of printer ink!

Here's a comparison to an LTV Scout B, also 1/96 scale. Amazing that little sucker could even make it to orbit. While of course the Delta IV is vastly more powerful, the comparison illustrates how bulky liquid hydrogen fuel is.
D4H - 25.jpg
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Paper has a grain associated with it much like a sheet of balsa. If you try to curl it across the grain it will crease. Try rolling a tube along a long edge of paper versus the short edge and you can see this right away.

Steaming helps bend the fibers a little before rolling a tube. But printed kits designed for a body tube should be printed to that you roll the paper along the long edge so you don’t bend the grain of the paper. You can always try to scan them and print them yourself to change the orientation and experiment for yourself.

Those are some good results!