Paper Transitions

[accooper]

I have tried my best for years to make a good paper transition, but they always come out crumby. I have used card stock, inkjet photo paper, with very bad results. Anyone have any secrets in this area they can share?

Andrew From Texas

 

[MarkII]

There are a couple of techniques that I use to get the material to form a nice even curve. The first one is to place the cut-out pattern a soft, but not too soft foam pad, such as a thick mouse pad, and curl the paper by rolling a smooth cylindrical object, such as a battery, over it. With a conical transition pattern, you will have to roll the cylinder in an arc to get the curve even all the way around.

The second technique is simpler but it requires more care. If the pattern isn't too big, I often just lay it on my index finger, with the apex near the tip of my finger, and use the finger as a form, pressing very slight bends into the paper with my thumb as I rotate the pattern all the way through the arc. You have to do this very gradually, with just very light pressure on the pattern, and repeat it several times. But with practice, you can reach the point when you can do it fairly quickly without much fuss.

Using either technique, I will eventually attempt to carefully bring the edges together to form the truncated cone. If I am still getting too much resistance, and the paper looks like it is about to crease, I back off and go back to pressing a curve into it. When you are pressing the curve, it is really important that you pay attention to both ends of the pattern (the two sides that are to be joined together) and get them well-curved too. Once I can finally bring the two sides together, I then start to "over-curve" the pattern by gradually rolling it into a tighter cone than it will eventually be. I do this with one end on the inside, and then do it it again with the other end on the inside. If you can do this enough, then when you release the paper it will form itself into a cone with the approximate size that you need, and you won't have to fight the ends to keep them together when you glue them.

The most important thing is to take your time and work the pattern into the shape of the cone gradually, and to never put a crease in it. If you do get a crease, then the best thing to do is to retrace the pattern onto another piece of material and start over again. Your skill at forming patterns into conical transitions will improve with practice, too. If you have an important piece that you are working on (and isn't every building project important anyway? ), then it can be very helpful to draw or print the pattern onto a few scrap pieces of material and use them to practice making the cone a few times before you attempt to make the real one. Also make sure that you are forming your transition to the right size by dry fitting it onto the tubes before you glue it together. The inner circumference should fit snug against the smaller tube, but not be so tight that you have to force the cone onto it. The large circumference should match the circumference of the larger tube without gaps. A tiny amount of overhang is OK, though, because that can be removed after everything is assembled and glued together. Gaps, though, are hard to fix, but it is possible to correct them. Be very careful handling the rocket after you install the paper transition, so that you don't accidentally press on it and dent it. Then take the rocket to a well-ventilated area and brush or spread water-thin CA over the paper transition (don't let any drip down onto the tubes). Give the CA plenty of time to cure; depending upon how much you put on, it could take awhile before every spot on the surface is cured. Don't lean directly over or right near the rocket when you are spreading out the CA. If you watch closely, you will be able to see "smoke" (actually, evaporating CA) rising off of the paper afterward. Wait much longer than you think you will need before you touch the transition. Once you can verify that all of the CA is cured, you can lightly sand the stiffened paper until it is reasonably smooth. If it seems to still be weak in areas, repeat the CA application.

MarkII

 

[hcmbanjo]

I agree with MarkII's shroud techniques.

Recently I was building the Zooch Soyuz. There are a LOT of small engine bell shrouds. After cutting them out I formed them in the palm of my hand with a sharpened dowel.
I set the paper shroud in my left hand palm, opposite the thumb and below my pinky finger in the fleshiest, softest part of my hand. The small end of the shroud faced up diagonally toward my index finger.
The dowel is pressed into and rolled over the shroud to the sides. The palm of your hand is soft enough there is little chance of creases.

Some recommend pulling the shroud over the sharp edge of a table top. I've used that technique but you can get creases if your down pull isn't smooth.

I usually make three or four extra shrouds then dry fit and pick the best one.

I've built too many of them over the years and have run accross a few kits that have supplied shroud stock too thick to roll smoothly. I had to remake the shroud using 110 lb. cardstock.

I don't use CA on the outside of the shroud. I'll use CA on the inside after forming and before gluing onto the adapter. This way the shroud is paper is strengthened and easier to finish.

 

[brianc]

In addition to the tips above, I've found the #1 tool for success (for
me anyway)- small clamps! Depending on the size of the transition,
I use small plastic (found at Lowes/Rocket Depot/etc), spring loaded
tweezers or hemostats.

Not having to use my fat fingers really helps with the alignment of
the edges and such.

 

[accooper]

Something no one has talked about in this thread is what is your favorite material to make the transitions from and what do you do about the seam?

Andrew

 

[luke strawwalker]

Something no one has talked about in this thread is what is your favorite material to make the transitions from and what do you do about the seam?

Andrew

I like to use 110 pound cardstock... seems to work pretty well. I've been building mostly Dr. Zooch kits for the past year and they usually have LOTS of paper transitions, some are just wraps for balsa transitions and some are genuine paper transitions unsupported from the back, and bunchs of them are used to make various rocket nozzles, which incidentally look AWESOME when they're done!

I've also used cereal box cardboard/stock (I tend to think "corrugated cardboard" when I say cardboard, 'cardstock' to me implies a flat sheet-type product) cut from old cereal boxes like Apple Jacks... I used that for the SRB aft-skirt on my Ares I 1/100 scale scratchbuilt I'm working on... and it looks great.

I usually harden ALL paper shrouds/nozzles with thin CA glue when I'm done-- turns them into a 'composite material' more like plastic than paper...

As for seams, Tim Van Milligan over at Apogee Components put out a handy-dandy construction tip video of making a paper shroud on his "Apogee Rocket Workshop" video tutorials on YouTube... you should be able to find a link either at the Apogee Rockets website www.apogeerockets.com or google or yahoo it or look it up on Youtube. They're pretty good vids BTW. He uses 'rubber contact cement' with a small 'backing flap' glued on the backside overlapping the edge of one side of the transition seam, and then glued the other side to the backing flap-- this eliminates the seam down to just a thin line that is EASILY filled, sanded, and painted over to be invisible. I haven't used that technique yet, but it looks like a good one. He hardens the whole thing with CA to stiffen the paper and also permanently 'set' the backing flap joint, since rubber contact cement isn't a particularly durable type of glue, although it's non-wrinkling non-warping properties make it VERY useful for this type of job, since white or yellow glues tend to wrinkle the long thin joints of paper shrouds.

I've made some with just an ordinary 'overlap' joint with a 'glue tab' on one end of the joint and gluing the other end of the transition directly over the glue tab to make the transition. You can harden it with CA after it's dried (using regular white/yellow glue on the flap) and then fill it like any other 'imperfection' using thinned Elmer's filler and sanding it down, and primering over it. That should hide the seam really well and make it invisible too. I WOULD harden the paper with CA first though, as water-thinned Elmer's filler would probably wrinkle it otherwise. Once it's CA hardened it should be pretty impervious to water from the filler. If in doubt, one could always go over it with a thin layer of yellow wood glue rubbed on with a finger to 'seal' the paper and then use moulding/trim glue to hide the seam, and prime/sand/paint normally. The TMTG might be a bit harder to sand than the filler though, as sanding white glue often leaves a bit of a 'rough surface' or rolls up little balls of hardened glue and other such stuff that Elmer's filler doesn't do.

Good luck and hope this helps! OL JR

PS... that's a plain printer-paper transition/nozzle shroud on the Ares I LES rocket nozzles in the third pic, hardened with CA. The SRB skirt is Apple Jacks box material hardened with CA... the Zooch nozzle is cardstock (110 lb IIRC) from the Discoverer Thor kit.

 

[luke strawwalker]

Couple more shots of the Dr. Zooch engine bells...

Way cool! OL JR

 

[Micromeister]

Couldn't agree more with Mark and Luke.

Taking our time is by far the most important part of making very nice paper and cardstock transitions.

Rolling over the edge of a table or curling on a soft foam pad make the fit-up easier. Than its time to decide if your going to taper the paper tabs to give a smooth seam. or cut them off and add an interior tab that mates both edges in a butt-on joint. or simple letting the overlap thickness be what it is and address it with filler, primers or sanding. All three techniques can work well depending on the amount of time you wish to spend.

You ask about material choice: there it totally depends on the model and size of the transition. They can be made from just about anything from onion skin traceing paper to 3/64th in 3 ply plywood. Most use standard 67 or 110lb Cardstock as these are most easily obtained. Many of the transititions I make are of different materials depending on the application. some taper very thin tracing vellums, papers or mylars. Most are rolled around a mandrel or hardwood dowel, just using an edge to work the roll into the paper as it goes. Long transitions and boattails are often reinfoced with water thin CA after attachment creating a sort-of phenolic of the paper.

If a seam is going to remain un-finished or exposed it can often be hidden under a fin or other attached part.

In the pics the very long almost 8" SS-N2 Styx boattail is file folder CA soaked sanded and painted, that fins are butt jointed directly to this cardstock transition, while the booster nozzle is 67lb cardstock wrapped with nylon thread in carpenters glue.
The oval transition of the micro cluster is mylar tracing vellum CA soaked, sanded and painted.

The interstage transition on the 3X laser-X is 3/64 3 ply plywood. while the standard model beside it has 110lb cardstock transition. So you see it really all depends on what the model is and how much pressure the transition or boattail has to take.

 

[MarkII]

Something no one has talked about in this thread is what is your favorite material to make the transitions from and what do you do about the seam?

Andrew

Georgia-Pacific 110 lb. white cardstock (about $5.25 for a ream of it at Walmart) is my all-around favorite. I just run it through my printer and print out the shroud pattern on it. I have also used 100 lb. Strathmore Smooth Bristol paper on occasion. It is much more expensive than the cardstock, but it is unrivaled (among papers) in structural integrity. (You won't need to put CA on it.) I bought a 9"x12" pad of 20 sheets of it at Michael's, but I don't remember what I paid for it. (Watch for those Michael's coupons in the paper!) I have used one sheet out of the pad so far. Another material that hasn't been mentioned is thin sheet styrene. Gluing it neatly can be tricky, though.

Most of the time I assemble the transition with a butt joint. The two edges are butted up against each other and glued together. For a butt joint to work with something like a transition shroud though, it needs more support. I cut an extra piece of material that is narrow and the same length as the shroud and glue half (lengthwise) if it to the back of one edge, then apply glue to the uncovered side of the strip, and bring the other edge around and bond the strip to it. This usually makes for a flatter seam. Make sure that the strip is not too wide, though, because if it is, it will create a flat spot in the cone at the seam. Put a small amount of white glue onto a paper plate, and then pick some of it up with the end of a toothpick and use the toothpick to spread an even, thin film of glue on the strip. Keep the layer of glue thin and even without clumps and not too thick. Too much glue will cause the paper or cardstock to wrinkle. Don't use wood glue; it will shrink and look ugly. White glue is the best choice for bonding paper to paper.

The other common method is to use a lap joint. Instead of bonding a strip to the inside of the cone, one edge has an extra tab on it that is glued on top of the other edge. If the material is thin, this extra thickness caused by the overlapping material at the seam can often be unnoticeable and it can be disguised by painting and finishing techniques. The advantage of using the lap joint is that it is stronger than the butt joint and is somewhat easier to create.

One other method that I have experimented with for gluing the cone together is to use rubber cement for the initial bonding. The advantage is that it gives me more working time, and if the two edges of the joint aren't quite lined up evenly, I can pull it apart and reposition them. The glue remains flexible, which enables me to recurve the area of the seam after I have created it in order to eliminate any flat spot. And if I get any stray glue on the paper where it shouldn't be, I just wait until it cures and then I simply rub it off with my finger. The rubber cement does not mar the paper because it does not soak into it. Now I know that you are thinking, "Wait, rubber cement isn't all that strong of an adhesive" and you are right; it isn't. But once I coat the shroud with CA, the CA soaks in and firmly bonds the joint. Using rubber cement allows me to continue working with the shroud, making it rounder and more even after I have glued it together, and it enables me to clean up any messy glue spots. As I said, I'm still experimenting with the technique, but it looks like it could be a viable answer in some situations.

BTW, I agree with Chris; when it is possible to do so, it can often be helpful to apply the CA to the inside of the cone before you glue it on. But it can also help to apply it on the outside, because that makes the paper sandable. Try it either way. Finally, one other way to make a VERY strong shroud is to make two of them, and size one to fit inside the other. Then bond them together.

MarkII

 

[stantonjtroy]

For rockets with a main tube of BT-60 or larger I like to use 1/64in ply, it holds it's shape wull and won't kink or wrinkle. Reciently I got my hands on some very thin (aprox 1/40 in) sheet G10. I just today rolled a boat tail for a 3" upscale bullpup. It turned out perfect, with very little effort.

 

[accooper]

I just printed out a transition pattern through my laser printer and it is curled to start with. That should help.

Thanks for the info.

Andrew