My exploration of papering techniques... I'm still not sold on it!

[Marc_G]

Hi everyone,

There have been a lot of discussions about papering fins for LPR/MPR purposes recently. I've been meaning to give it another try, since my earlier experiments at papering did not go well.

I've read up on a variety of papering techniques, with special thanks to JR for his detailed explanations, CaveDuck for his insights but on the forum and in PMs, and everyone else who has bothered to post their technique.

I will review here what I did and what the results were like.

It starts with: what do I want to get out of papering that I don't get by just cutting out the fin and sticking it on the tube:

1. Reduced effort finishing the fins to eliminate wood grain
2. Strengthen them... what matters to me is resistance to dings and chips in flight and landing.
3. A low weight solution would be optimal

My usuall method is to attach the fins to the tube, soak in thin CA, and then depending on the graininess, use Carpenter's Wood Filler (CWF), spot primer (Bondo/3M), or simply a heavy spray of filler primer. Of course, sanding the fins after they are attached can be a challenge in all but the simplest situations. Actually I've gotten pretty good at it, but I'm always looking for better ways.

I'm planning an Icarus build, and a Maxi Icarus, so I decided to use the very simple fin pattern as a testing ground.

I decided to test Elmer's Glue All, Titebond Molding and Trim Wood Glue, and thin cyanoacrylate glue (CA).

Conspicuously absent from my tests is the simple matter of using self adhesive label paper. I've done this before with success, more or less, but I find that these fins aren't much stronger or dent resistant than normal. But it's a good easy lightweight technique, particularly if you heat-activate the glue with a warm (not hot) iron or something similar. Sometimes the grain shows through, in my experiements.​

I cut out 9 fins and a few spares. Then I assembled the things I would need:



The glass is not for the soda, but will be used as a rolling pin of sorts. The risks of being found using my wife's nice marble rolling pin are too great...

 

[Marc_G]

I weighed the fins. A set of three weighs 1.6 grams. Note, the fins have rounded leading edges but are square edged otherwise.

I traced the fin on 20 lb inkjet printer paper which I had quartered, then kind of rolled the fin over the leading edge line and traced the other side. The result is sort of a taco shell shape when folded, but for now I left it flat. I took some Elmer's Glue All and spread a line of it at one edge of the fin tracing on the paper. Using the keycard, I spread the glue quite thin on the paper, just like many others have directed. I made sure that it was kind of thin and still kind of wet-ish. I gave the thing maybe 2-3 passes with the keycard, then pressed the fin onto it's traced location, without being paranoid about it. Then I gave the same glue spreading treatment to the other side of the fin tracing, and folded it over.



I used the rolling pin glass and made sure it was nice and smooth.



Then I cut most of the excess paper away with scissors. I didn't want to risk cutting damp paper with the Xacto knife for fear of it tearing.



When all three fins were done, I pressed them under glass.



I've read a lot about pressing under glass and always wondered how thing dried this way, being largely cut off from the air. Answer: they don't. The fins were still just as damp in the next morning. Edge drying effects or the impact of the air in the fins themselves certainly didn't result in the fins drying while pressed.

 

[Marc_G]

I then did another set, using the same technique, except this time I used the Molding and Trim glue.

They went under glass with the others:



Yes, I labeled them so that I could keep track of them :wink:

 

[KenRico]

Thanks for the feedback, CaveDuck has been sharin g with me too.

For my renegade f I used 1/64 inch ply instead of paper . It is strong but think I will reserve this for fins that the leading edge or trailing edge are shaped to a point as the paper and tissue peel back during finish sanding. Like paper you can cut this plywood with scissors so can cut eliptical and such. Also good for liteply crs to add some shear tollerance but doesnt add a lot of weight .

I like the way it turned out but is a little pricey for every rocket and heavier than paper . Would like to turn more or my lpr and paper mpr to ttw. Like executioner without having to cut all new fins so this is looking like a good solution to build up the fin and more importantly the tab.

Kenny

 

[Marc_G]

While those "dried" I decided to try the CA technique CaveDuck had recommended to me.

It goes like this:
0. Coat the root edges with some wood glue and allow to soak in and dry. This way, any CA that soaks in won't interfere with the bond.
1. Spray some Formula 77 spray adhesive onto regular printer paper. Very light coat, just to make it a little tacky. (I'd show a picture, but it would look just like a piece of printer paper)
2. Trace the fin like I described above. There are two options:
3a. Cut out the taco shape, then put the fin on, fold over, and use an exacto knife to trim it:

Or,
3b. Don't do the taco fold, but instead apply the two paper sides separately. This works fine too... I only did one fin this way, but I prefered the taco method given the rounded leading edge for an easy roll-over.
Either way, the light tack from the formula 77 spray holds the paper to the wood, without being overly gummy.

4. Use appropriate ventilation and protective gear. Soak in to saturation with thin CA (pink bottle at the Hobby Lobby) . I used a qtip to wipe it around, adding more until it seemed saturated. I left the thing on a sheet of glass to dry the first side before turning and doing the other side.

I goofed on one of them and got the edge stuck to the glass, causing a rip:



But I was able to trim that away, apply a drop of thick CA, and let dry overnight. Then I sanded the hard surface down to flush with the adjacent surface... the painted surface would not show the error.

 

[Marc_G]

(I'll document more later... gotta run for now!)

 

[Marc_G]

The next morning, I took the Glue-All and TMTWG fins out from between the glass shelves.

As I mentioned above, they were still damp. I set them on a table, tilted up with one side of each supported by a wood dowel. The idea was that this would allow both sides to dry evenly. There was no warping either right when I took them out, or after they were dry a few hours later (I was able to monitor the drying by weighing them periodically... at some point the weight became stable).

Here is the first set, done with Elmer's Glue All. Ignore the note that says white glue... chalk it up to a brain fart.



As you can see, one of them suffered from poor attachment on one side. Otherwise, they came out pretty well. It was pretty easy to trim them, but I would probably want to swab the trailing and tip edges with CA then sand them smooth. Not just to seal the edges, but to make sure I don't have little fibers sticking out. I eventually used a bit of Glue All to reattach the paper to the wood, and set it under something heavy for a while then took it out to dry.
This set was pretty easy to trim with an Xacto blade once the glue had dried.

The next set, done with TMTWG (aka TMTG), was much harder to trim because the glue was a bit thicker and tougher on the paper at the edges. However,
the paper seemed very well adhered to the wood. Same comments about feeling I need to CA the edges and sand.

 

[Marc_G]

Here is the CA set:



They worked out very well, nice and smooth. A quick pass over 400 grit paper left them velvety smooth. The torn section I mentioned before was just about perfectly smoothed into the adjacent surface by some thick CA and sanding.
These fins are very hard, rigid, and would take paint just fine. No worries about them being dented easily. They are definitely harder than the Glue All or TMTWG sets.

Finally, I tried one more thing for comparison: I took a sheet of basswood, that had been sealed as a full sheet with Rustoleum Auto Filler Primer, then sanded down. I cut a set of fins in the same dimensions, and rounded the leading edge. On this set I also rounded the trailing edge, but the set was otherwise identical to the other three:



These are very nice. Smooth, hard, easy to shape...

Tomorrow I will post weights and some further observations.

 

[luke strawwalker]

Interesting ideas... thanks for posting this.

I agree that the glass is a total waste of time. If you do the "wrap over the leading edge" method, there's really no danger of warpage anyway, because the fins have glue (and thus moisture) on both sides simultaneously, and therefore any tendency to warp is "balanced out". And, as you correctly pointed out, the glass cuts off virtually ALL the routes for the moisture to escape from the fin and allow the glue to dry... My first experiments in papering fins, I used some stacked books, but like your experience, they slowed the drying progress considerably (not as bad as glass would I think!) After that I papered fins without it and no worries-- the dried fine overnight and no warpage.

On the "tumbler as rolling pin" idea... I think this is part of your problem-- the REAL TRICK to papering fins is twofold-- 1) you have to use a VERY THIN layer of glue-- it should be "sticky" after applying it, but NOT WET... if it's wet, you've got TOO MUCH glue. I know, you'll think, "this little bit of glue can't POSSIBLY bond", but it DOES... (so long as you put the balsa and paper together immediately after spreading the glue out very thinly-- I personally just use my index finger to spread the Elmer's Glue-ALL (white glue) over the paper, and when it starts to feel more sticky than wet, almost like it's about to stick my finger down, that's when I push the fin down onto the paper firmly, and start applying the glue to either the upper surface of the fin, or to the opposite tracing of the fin on the paper above the leading edge... I don't bother with "spatulas" or credit cards or anything because in my experience it's too hard to get a VERY VERY THIN layer of glue... they tend to 'float' more and leave more glue behind, PLUS, your finger is warm-- it helps the glue to "dry out" a bit and tack up when spread very very thinly, and you get the tactile feedback of when the glue layer is JUST RIGHT.

Using a tumbler as a rolling pin is creative, but I think it contributes to your problems, honestly... A glass is a VERY large diameter object, and larger diameter objects generally exert less surface pressure than smaller diameter objects (or the larger ones spread the force out over a MUCH larger area). The second REAL TRICK to papering fins is, once the paper is applied, to BURNISH IT DOWN VERY TIGHT ONTO THE WOOD! You want to squeeze out absolutely ALL the excess glue from between the paper and the wood... don't worry, enough will remain to lock the paper down onto the wood permanently... To really do a GOOD job burnishing the fin down, you need a SMALLER DIAMETER burnishing tool... I've found that a regular old gray and black-capped Sharpie markers works WONDERFULLY well for burnishing down the paper onto the fins-- the surface of the marker is rounded, but small (maybe 3/8 inch diameter or so) which is IDEAL for applying pressure to the fin... and there's a technique to it... start from the CENTER of the LEADING EDGE of the fin, and work OUTWARDS AND BACKWARDS across the surface of the fin, holding the pen flat against the fin, and simply SLIDING it across the paper towards the back and root and tip edges of the fin... you DON'T have to "roll" the fin, although you CAN. If you use too much glue, the paper will get "wet" and be VERY soft and prone to tearing or wrinkling... that's why a THIN coat of glue is absolutely essential. Even when you think you have the glue layer "too thin" when you stick the fin down onto the paper, or fold it over onto the second half of the paper, you'll be AMAZED at how much glue you'll squeeze out with a PROPER burnishing job... It's basically the same process as floating out drywall mud or putting up wallpaper-- you want it to be worked down TIGHT against the wood, to eliminate all air/glue bubbles and to ensure a good TIGHT bond to the wood (the thinner the glue layer, the stronger the bond, in glue joints... it seems counterintuitive, but it's true!). Once you burnish the entire surface of the fin, flip and repeat in the same manner on the other side of the fin. Once I've finished BOTH SIDES of the fin, I then run the ROUNDED TIP of the Sharpie marker, opposite the cap end, over and around the edge of the fin, all the way around. I cut my paper to have at least a half-inch of paper all the way around once the fin is covered in paper... (except the leading edge, which is where the fin is folded over onto the other side of the fin to paper both sides at once). This burnishing the paper over the edge does a couple things for you-- it ENSURES that the edges are LOCKED DOWN TIGHT against the wood, and the glue that's squeezed out from between the wood and paper that's trapped in this area is evenly spread, and glues the paper to itself, ESPECIALLY if you airfoil the back edge of the fin (taper it down to the classical "teardrop" airfoil). The paper will be glued down to itself TIGHT, completely locking the fin inside the paper, and in the case of the trailing edge, this will be a benefit later when we cut the excess paper off the fin, because we can leave a TINY STRIP of the paper glued to itself just past the edge of the wood to ENSURE that it stays locked together, if we desire, or we can cut it off flush with the back edge of the fin if we want... up to you... Be sure you flip and BURNISH THE EDGES ON BOTH SIDES OF THE FIN... don't worry that it'll end up "flat" on the table on the opposite side you just burnished, while the side you're burnishing presently will be curved over the edge of the paper... it all balances out while drying and the paper will be stuck down TIGHT over the edges when you're done...

Now, SET THEM ASIDE TO DRY COMPLETELY... I notice you said you started cutting off the excess paper right after applying the paper, after rolling them under the glass... Honestly I'm pretty sure THIS is part of your problem too... wet paper doesn't cut worth a darn, and messing with them at this point is just going to mess something up, not make it better-- you've applied the paper, got it burnished down TIGHT with an ULTRA-THIN layer of glue, now's the time to let the adhesive do it's job, and set up, and lock everything together permanently. I just set the fins aside, leaned up against the kit box overnight to dry, in most cases... the excess paper won't hurt ANYTHING at this point, in fact, it works in your favor, due to the burnishing around the edges, gluing the paper to itself.

The next day, when the glue is TOTALLY dry, THEN use scissors to take off the excess paper down to about 1/4 inch or so of the edge of the wood, then CAREFULLY SHAVE the rest of the scrap paper off the edges down to the wood using a SHARP hobby knife... Go slowly and carefully, and you can shave right down to the edge of the wood in one step... if you're afraid you'll nick the edges of the wood, shave the paper off down to within about 1/16 inch of the wood, and then go back and, resting the side of the blade against the wood itself, carefully shave off that last 1/16 inch of paper by cutting toward the wood... if you have a sharp #11 blade, it'll shave off in a pretty little curly-Q pretty as you please, easy-peasy... Decide how you close you want to shave the paper to the trailing edge, and then carefully shave that down as well. Shave the paper down completely to the edge of the wood on the tip and root edges of the fin.

If there are any "hairs" or bits of paper or glue that didn't quite shave off cleanly, holding the fin edge against a sheet of 220 grit sandpaper on your workbench and, tilting it at a SLIGHT angle to put the contact with the sandpaper precisely on the fin edge, with slight downward pressure on the fin, draw the fin towards you a time or two-- DO NOT sand "back and forth"... do it like you'd sharpen a knife-- in one direction ONLY, draw the fin toward you, lift the fin and go back to the opposite side of the sandpaper, and do it again... inspect, and repeat until the edge is as clean as you want, and repeat for the other side of the tip edge and root edges, and you can similarly dress the trailing edge if you desire...

I notice the paper doesn't go all the way to the root edge of your fin-- I take it you "pre-cut" the paper to leave the edge more exposed for filleting?? I've found that's really not necessary and complicates the papering process... paper is, after all, wood, albeit reformulated wood... and white glue is compatible with wood glue used to attach the fins to the tube and the structural fillets (and with TMTG if you're using that for fillets as well). Well burnished-down paper glued to the fins will hold a fillet just as strongly as if the yellow glue or TMTG were applied directly to the fin wood itself. I've had a papered fin (edge to edge papered-- no exposed wood except on the root face and tip face of the fin) glued to the tube with yellow wood glue and filleted with TMTG go squirrely on an upper stage flight one time, and hit the ground at a high rate of speed UNDER POWER, basically coming down horizontally RIGHT ONTO THE EDGE OF THE FIN, and it ripped the fin off the rocket, alright-- BUT IT TOOK ABOUT HALF THE THICKNESS OF THE TUBE WITH IT! Also, this glue joint did NOT fail until the outer half of the fin and paper were ground to dust from the impact before the tube wall itself FINALLY gave way-- the GLUE JOINT DID NOT FAIL!! When your glue joint is STRONGER than the paper tube to which it is applied-- well, you cannot get any stronger than that! (it's pointless to try for "stronger" because, like the chain, it's going to fail SOMEWHERE, (at the weakest link) and so long as the glue joint isn't the weakest link, that's all you can ask for... BY THE WAY, these were DOUBLE-GLUE JOINTS... another procedure I HIGHLY RECOMMEND!)

Now, I hear ya, that you want substantially STRONGER fins than balsa alone... balsa is notoriously soft and easily dinged, dented, or crushed... and paper adds some strength, but only so much... You have a couple choices...

One is, going with THICKER PAPER-- switching to 60 pound or 110 pound cardstock instead of regular 20 pound printer paper should add considerable strength. Might make working the paper down a bit harder though, but it should also make a harder surface VERY resistant to balsa dings...

OR, you COULD CA the balsa fin BEFORE papering-- as you said, lay down a layer of wood glue along the root edge and let it soak in and dry (the first step in double-glue joints BTW) and THEN soak the fin with the ultra-thin pink bottle CA, let that cure, and THEN paper the fin... I've never tried it this way, but the white glue SHOULD hold the paper onto the fin in the same manner-- probably not AS strongly, but if the fin isn't sanded, the CA tends to raise the 'balsa hairs' and dust and crud on even the most meticulously cleaned balsa surface, and should provide plenty of "tooth" for the white glue to lock the paper onto the fin (so long as the "grit" from the CA doesn't show through, but I think that's unlikely... you'd have to experiment here to do see how that works...

The other alternative is, paper the fin normally as I described, then, once it's completely finished, THEN drench the surface of the PAPER with CA... the CA should soak into the exposed layers of the paper and the edges of the fin (especially the tip and trailing edges which are exposed-- again, presuming you have already applied wood glue to the root edge and allowed it to dry as the first step of the double-glue joint to glue the fin onto the rocket later). The CA should harden up the surface of the paper into a composite material something like fiberglass, on a smaller scale-- instead of glass fibers and epoxy resin, you have paper fibers and CA resin... just the same way you'd harden up a paper shroud or transition on a build by soaking it with CA...

Of course, balsa will always be balsa... we can "harden" it with CA, but it's just flat never going to be as strong as something harder... even papered... if you're REALLY wanting a hard fin material that will be the MOST resistant to crushing or dent damage in flight or landing, you should probably just switch to basswood and call it good... basswood is MUCH more resistant to crushing and dinging and denting than balsa will EVER be, no matter WHAT the balsa is treated with...

I'd give these techniques a try before I really passed judgement on the whole papering thing-- there are reasons why some things work better than others... and if you want a more 'dent resistant' surface, well, you may have to experiment even more to find what you like...

Good luck with your projects! OL JR

 

[Marc_G]

Work and family stuff has slowed me down but I will continue the thread in a day or three...

 

[Marc_G]

OK, I finally got back to this.

Recall that each set of plain balsa fins weighs 1.6g per set of 3 fins. Here are the final weights of each set, as they stand ready to take paint:

Elmer's Glue All:	3.1g
TMTWG:	4.1g
Thin CA:	4.6g
Basswood:	7.0g

The basswood fins were cut from a sheet that had been sprayed with Rusto filler primer, sanded with an orbital sander briefly, sprayed again, and sanded. Not counting drying time, the whole sheet took about 5 minutes of effort.

 

[Marc_G]

For the "finish test" I took one of each fin and taped it to a piece of cardboard:





Note that the paper edge trimming job on the Glue All and TMTWG set wasn't as pretty as the CA set... I learned along the way. I could do a much better job today in trimming. So, please ignore the weak trimming job on these two.

I sprayed a coat of Auto Air Sealer White (an acrylic white primer, you could call it) which is my standard base coat for any rocket these days when I topcoat with acrylics. Note, this being a primarily aquaeous paint, it does create the possibility of wrinkling or warping. However, I didn't notice such effects on any of the fins.





The hard part for me is capturing the results photographically. Angle and lighting are a big deal.

In short, all the fins were usable if I wanted to. The Glue-All had noticeable grain show-through, but it wasn't bad. For the amount of effort put in, and considering this was my first shot, it got rid of ~80% of the graininess with very low effort.

The TMTWG fin was noticeably better. About 90+% of the graininess removed.

The CA-papered and Basswood fins might have been molded from smooth plastic.

 

[Marc_G]

(More documentation to follow later)

 

[GDJ]

Interesting read, and I can confirm to a certain extent of what you are publishing here.

I don't feel that glass is a waste of time. It has certain advantages, like rigidity, weight, and you can readily see what the glue is doing (ie spreading out evenly, layers are staying aligned, etc) but in order to be really effective, the glass has to be fairly thick (at least 10mm thick). Also the thicker the glass, the better it can withstand some weights being placed on it to get a tighter fin assembly, and force out any air bubbles or thicker blobs of glue that would be trapped between the layers.

I have done a variation of the glass plate method by using 2x6 cut in 1 foot lengths, gluing them together (so I would have 2 pieces of 4x6 effectively) and using those with large C-clamps to compress the fins while the glue sets up, either with papering or using 1/64" birch. Cardstock on balsa fins works well, but for real rigidity the 1/64" birch with balsa fins is really hard to beat. You still have the weight advantage of balsa fins (just a touch heavier) but the rigidity goes "thru the roof". The difference is akin to comparing a sheet of aluminium to a sheet of high carbon steel.

 

[bradycros]

The next morning, I took the Glue-All and TMTWG fins out from between the glass shelves.

As I mentioned above, they were still damp. I set them on a table, tilted up with one side of each supported by a wood dowel. The idea was that this would allow both sides to dry evenly. There was no warping either right when I took them out, or after they were dry a few hours later (I was able to monitor the drying by weighing them periodically... at some point the weight became stable).

Here is the first set, done with Elmer's Glue All. Ignore the note that says white glue... chalk it up to a brain fart.

You might try using pieces of glass that aren't more then a few inches bigger then the area the fins are taking up. I have pointed a small fan at the space seperating the two pieces of glass over night. Worked for me.

 

[Marc_G]

Next, I decided to test the degree of hardness of the various fins.

I used my thumnail and attempted to create a dent in the fin, running along the grain. Of course plain balsa would easily dent this way, and I've found that using label paper with no additional glue imparts a little bit of resistance but not much.

The Glue-All -papered fin easily dented. It was certainly harder than plain balsa, but it still dented pretty easily.

The TMTWG -papered fin was a little more resiliant, but still took a dent pretty easily.

The CA-papered fin did not take a dent, even with me pressing pretty hard with my fingernail.

The basswood fin also was very resiliant. Pressing very hard, I could make the smallest of impressions, but it was really quite hard.

 

[Marc_G]

So, where does all this leave me?

I might need to adjust the title, because I think I'm more likely to paper now than I was...

From what I've learned, I will probably less frequently use my go-to technique of attaching fins, sealing with CA, then filling with CWF or spot putty, with lots of sanding.

The technique I use for future builds will depend on what I'm doing. Let's review:

Scratch builds:

• For simple geometric fin shapes like Icarus, I would most likely just use basswood fins cut from a sheet finished with filler primer and an orbital sander
• If I was particularly concerned with weight, I'd go with papering probably with self adhesive label paper.
• If the fins were composites of several pieces cut out, such as Vagabond style with a main fin, and an attached strake and lagging triangular bit, I would probably use balsa with the papering with CA method.

Kits with supplied fins:

• Most likely I would go with the papering with CA method. Quick, easy, and very good coverage of the grain.
• Adhesive papering (label paper) would be my go-to if weight was a concern
• If I needed particularly good coverage of dings or something, I would paper with TMTWG then perhaps overcoat with thin CA

Of course, this is just my own analysis based on my own skills and priorities. I'm not saying what's the right way, just how I would probably do it.

I really like how quickly the CA-papered fins dried and were ready for use, and the fact that I could do minor sanding if need be without worries of fibers from the paper sticking out... the CA/paper composite is sandable without fibers sticking out.

Part of my own rationale is driven by the fact that I mostly use water-based acrylic paints (including white/dark sealer) with my airbrush. I love these paints but you can't sand them, at least not much. They dry much softer than lacquers or even enamels, so to get a smooth paint job, the surface has to be impeccable. Also, the paint itself isn't a good "sealer" and the surface must be well sealed before painting.