Fin Alignment

I started on Baby Bertha and got two fins mounted. I didn't think they looked perfect. So I decided to buy the Estes Fin Alignment kit. Went on ebay and got a good deal.

Kit arrives and sure enough my two fins were way off. I carefully removed them, sanded and using the kit mounted all 4 fins. Way easy with the kit. Just the thing for a tyro like me.

Question, when glueing balsa wood fin to paper tube which is better to use Wlmers White glue or Tritebond Wood Glue? Or, something else?

Tritebond? That would have made a great "Wacky Pack" graphic, back in the day! :roll:

Personally I prefer a very shrinky wood glue like Carpenter's Glue by Elmers. I don't particularly like Titebond II as it doesn't shrink. I don't have experience with original Titebond so can't comment on it. In this application (fin to tube), the shrinking makes for a more rigid, tighter bond IMHO. I like Titebond II for couplers and centering rings specifically because it doesn't shrink and cause Coke-bottle effect.

Elmers White Glue will be fine too. It will hold plenty strong too.

For fillets I recommend Titebond Moulding and Trim Wood Glue. It doesn't shrink, and it's thick enough not to run. Stays where you put it.

Marc

Elmer's Glue-All or Titebond II? The answer is "yes" to both. They will both do a fine job.

Once it has set, Titebond II produces an absolutely bullet-proof, unmovable bond. Wood glue usually requires a period of clamping before it achieves a secure enough bond, though.

With that being said, there are are a couple of factors in white glue's favor. First of all, it usually looks neater and smoother than wood glue, especially bright yellow TB II. Second, the bond can be softened and then allowed to re-harden with no loss of strength. This can be helpful in some situations, such as with fins. If the tilt of a fin in relationship to the body tube ends up being something other than 90°, you can heat up the joint with a hair dryer just enough to soften the white glue a little, which will allow you to (gently!) adjust the fin orientation. (It helps to do this before you have applied fillets to them.) When the glue cools down and re-hardens it will be as strong as it was before.

White glue, like wood glue, will create a very secure bond between the bare balsa of the fin root and the paper surface of the body tube. The ability of white glue to be softened with heat can be a problem, though, if you live in parts of the country that get oven-like heat during the summer. (Hello, Texas and Arizona.) If your rocket sits out in the sun too long, or is kept in a hot car for an extended period of time, the fins can loosen and even debond in the heat.* In those environments, wood glue is probably your best choice.



*Note: it takes prolonged exposure to a very hot environment to do that. The phenomenon has never actually happened to me personally, even when I lived in regions that were on average much warmer than where I live now. But others, especially people living in the Southwest and the Plains, have experienced it, so it does indeed happen.

Thanks for all the advice! I never knew White glue could be heated and softened. Good to know.

:2:I use CA on most everything then titebond III for fillets.Just drag some sandpaper across the BT a few times

Reddwarf said:

I started on Baby Bertha and got two fins mounted. I didn't think they looked perfect. So I decided to buy the Estes Fin Alignment kit. Went on ebay and got a good deal.

Kit arrives and sure enough my two fins were way off. I carefully removed them, sanded and using the kit mounted all 4 fins. Way easy with the kit. Just the thing for a tyro like me.

Question, when glueing balsa wood fin to paper tube which is better to use Wlmers White glue or Tritebond Wood Glue? Or, something else?

Click to expand...

For fins, Titebond II will give a stronger joint than the Elmer's will. Use a double-glue joint and the fins go on fast and strong. Apply a thin layer of Titebond to the fin roots. Using an old egg carton from the refrigerator that you've inverted and slit the egg cups perpendicular to the long axis of the carton with your hobby knife, stick the fin tips into the slits and they'll hold the fins level while the glue on the root edges dries... a thin layer is all you need, and it only takes about 10-15 minutes or so to dry... doesn't have to be "hard dry". At the same time, apply a thin bead of glue to the fin lines on the tube, and smear it thinly and evenly down the fin line with your finger so it's spread out a little... for even greater strength, you can sand the fin lines lightly with a little 220 grit sandpaper to rough up the glassine and give the glue more "tooth" to grab onto. You only need to sand up and down the fin line a few passes, not sand the line completely off. Set the tube aside to dry while the fins are drying. After 15 minutes or so, the fins are ready to go on the tube... Apply a SECOND fairly thin bead of glue to the fin root edges, and spread it evenly with your finger over the width of the fin root. Take the fin in one hand and the tube in the other, carefully align the fin to the marks and lines on the tube, (or the rear tube edge, whatever you're using for a fore-and-aft aligment) and then put the back edge of the fin to the tube, and align the fin with the fin line at the front, and gently tilt the fin foward til the front end of the root edge is against the tube. Hold it about ten seconds, and PRESTO the yellow glue will "lock" the fin in place just like you used super-glue, but with about double the strength. Repeat for the rest of your fins. Spread any yellow glue squeezed out from under the fin root with your finger along the joint on either side of the fin... sometimes I add a little glue and make first-pass "mini-fillets" at this time to make sure everything is spread evenly and smoothly, as usually not enough glue is squeezed out to make a continuous mini-fillet. Since you have the fin alignment guide, you can now install the rocket over the guide and gently clip the fins in place... there will still be enough play in them (the glue is still soft enough) to allow the fins to be gently pulled into position by the guide before the glue sets up hard... This style of joint is AMAZINGLY strong... the balsa will break or the outer layer of the tube will rip off before the glue turns loose... I've seen it myself. Works like a champ.

For the strongest fins, paper them. Simply smear a THIN layer of white glue (the thinner the better so long as they are completely and evenly coated) on one side of the fin, lay it on a sheet of printer paper with the LEADING EDGE of the fin toward the center of the paper, apply another THIN layer of glue evenly and completely to the side of the fin facing up, and, keeping the paper taut, fold the fin and paper over at the leading edge of the fin. Works even better if you've sanded whatever airfoil you want (rounded leading edge, tapered trailing edge, whatever) into the balsa beforehand. Use a sharpie marker or other round smooth object to "burnish" the paper down TIGHT to the fin and squeeze out any excess glue (yes there's always excess) starting in the center of the leading edge and working back and out to the root and tip edges of the fin toward the trailing edge, sorta like a rolling pin making pie crust... flip the fin and repeat. For this type of application, white glue works MUCH better than yellow wood glue like Titebond. Also, don't use SCHOOL GLUE, get the ELmer's "GLUE ALL" white glue as it's much stronger.

Yellow wood glues like Titebond are better for wood/paper joints in most cases, but for papering fins white glue works better due to its properties. Wood glue is also more resistant to heat softening than white glue, so I prefer to use it to glue the rings to the motor tube in a kit... BUT, when gluing the motor mount centering rings into the rocket body tube, DO NOT use yellow wood glue... it will shrink and "suck in" the tube around the centering rings, leaving an ugly 'depression' on the outer surface of the tube where the ring is inside the body tube. White glue does not shrink as severely and doesn't create this unsightly "pinch" in the tube wall. Besides, out by the body tube, the rings aren't subjected to much heat at all (due to the excellent heat insulating properties of the rings themselves and limited time for heat to travel from the motor tubes outwards) plus this joint has a LOT more surface area being between the outer edge of the ring and the larger body tube, so white glue is sufficiently strong in this instance. Also, DO NOT use yellow wood glue to glue in tube couplers or other tight fitting parts (like centering rings inside tubes). When spread thin between wicking materials (like tube couplers) it dries ALMOST INSTANTLY and can "lock" the parts in place BEFORE you get them slid into position... this is usually a DISASTER in the construction of your rocket.

White glue (Glue-ALL, Aileenes, etc) is superior for paper/paper joints, in most cases. For most wood/paper joints, yellow glue is superior, except in the case of paper skinning fins. Also, since white glue doesn't shrink as much, it's superior for gluing in motor mounts inside the tube as mentioned. Also, white glue doesn't "grab" as fast or hard when inserting tube couplers or other tight fitting components into tubes, so it's a better glue to use in these applications, as mentioned.

Good luck! OL JR

You guys are all clueless. Obviously, you should use epoxy! :neener: (Kidding! Just kidding!)
I actually put a small amount of thick CA on part of the root edge, then put Titebond wood glue on the rest of the fin root. This does help keep the fins more ridged in the event of the wood glue getting soft. This actually has happened to me the past couple of launches I've been to; it gets very hot in Florida in the summer, but we launch anyway! It does help to keep your rockets under a shade. The glue only softens while they're out in the sun waiting to be recovered. It's really not that uncommon for paint to get sticky from the heat and humidity, too.

I didn't know that about Elmers glue shrinking more than Titebond. I might have to get some of that.

Marc_G said:

Tritebond? That would have made a great "Wacky Pack" graphic, back in the day! :roll:

Personally I prefer a very shrinky wood glue like Carpenter's Glue by Elmers. I don't particularly like Titebond II as it doesn't shrink. I don't have experience with original Titebond so can't comment on it. In this application (fin to tube), the shrinking makes for a more rigid, tighter bond IMHO. I like Titebond II for couplers and centering rings specifically because it doesn't shrink and cause Coke-bottle effect.

Elmers White Glue will be fine too. It will hold plenty strong too.

For fillets I recommend Titebond Moulding and Trim Wood Glue. It doesn't shrink, and it's thick enough not to run. Stays where you put it.

Marc

Click to expand...

Don't know where you got Titebond that doesn't shrink (other than the Moulding and Trim "wood glue" which is actually sort of a thickened white glue, and works WONDERFULLY well for fillets!) Regular yellow titebond II is my preferred adhesive... it doesn't shrink QUITE as much as Elmer's yellow, but it DEFINITELY DOES shrink more than white glue! It WILL cause the "coke bottle effect" and suck in the tube wall around the centering ring if you use it to install a motor mount, especially if you use quite a bit to "fillet" round the internal ring/wall joint.

I don't see how the 'shrink' amount has anything to do with how strong the joint is. Glues that shrink usually cause more problems than they solve. The absolute strongest fin joint you can get from yellow glue is double glue joints, and I speak from experience here... I've had a second stage of a rocket come down horizontally and impact the ground at high speed with a fin pointing down... the fin had been papered for strength, and when it impacted it obliterated the outer forward 1/4 of the fin before the loads finally exceeded the strength of the tube wall and the outer layer of glassine and first layer of spiral-wound paper ripped off the underlying layers, right at the edge of the fillet areas... the glue joint itself never failed-- it was stronger than the balsa and paper tubing it was bonded to! No need in trying to get stronger than that! (weakest link breaks first ya know!)

Later and good luck! OL JR

Barracuda said:

:2:I use CA on most everything then titebond III for fillets.Just drag some sandpaper across the BT a few times

Click to expand...

CA is probably the WORST adhesive you can use for most rocketry gluing needs... it's very strong in TENSION but very weak in the SHEAR planes... which EXACTLY the kind of forces our rockets experience when the fins hit the ground descending under a parachute... PLUS, CA becomes brittle with age. I keep some around, but strictly for emergency repairs and tacking on detail parts (though I don't even usually like it for that) and for hardening balsa parts like nosecones and transitions to help them resist dings.

Double-glue joint using wood glue are ALMOST as fast drying as CA gluing the fins on, but the joint strength is probably double or more that of CA, and it doesn't embrittle with age. Also no fumes or risk of gluing your fingers to the fin or tube. CA seals off the grain of balsa, so that once CA is applied to a fin, other glue cannot penetrate and from a good bond... (I've heard of poeple "tacking" their fins on with CA and then filleting with wood glue and thinking they're getting a good bond, but it ain't so-- maybe mechanical strength from thick wood glue fillets, but sooner or later the wood WILL bust free of the wood glue because the wood glue can't penetrate CA-sealed wood grain!)

CA has a few SPECIALTY uses for hardening paper tube ends and fins and nosecones and such, but that's about it, IMHO...

Later! OL JR

I use Aleene's Tacky Glue (the gold-bottle stuff) for almost all LPR paper-paper and balsa-paper glue joints. As the name implies, it grabs fairly quickly, but not quite instantly, so you can nudge a fin over a millimeter or so if it's a bit off -- as long as you don't wait more than 15 seconds or so. After a minute or so it's usually set.

G. Harry Stine was a big booster of Aleene's in the HBOMR so that's good enough for me.

Yellow glues as several have mentioned do lock up almost instantly so they're kind of risky on motor mounts -- you pretty much have to nail it on the first try. Aleene's as well as Elmer's Glue-All and other white glues do allow you a few seconds before they lock up so you can edge it up or down a bit if you have to.

The yellow glues as others also have noted eventually shrink, sometimes creating unsightly crimps or ridges on body tubes where motor mounts are glued inside.

As Luke says above, don't use "school glues" -- IMO they are basically white glues watered down to make them easier to wash out of school clothes (and also cheaper), which also makes them weaker, slower to set and more liable to cracking.

CA I usually use only for plastic-to-balsa or plastic-to-paper joints.

For clarification to my above post, I use the double-glue method just as described above. It's the surefire way to get a fin on in good order without glue dripping all over the place and the fin wiggling around before the glue sets up.

As to the "Titebond II doesn't shrink--- or does it?" question, I learned here on the forum that Titebond II (specifically the II formulation) is a lot less shrinky than some other yellow glues. I've observed the Coke-bottle effect quite a bit when using Elmers Carpenters wood glue but never when using Titebond II. I learned about the shrink variance in the glue formulas here on the forum, and tested it out in several ways, including fin papering, filletting, and the centering ring applicaiton. In all cases, you could see the Carpenter's glue (Elmers) shrink considerably while the Titebond II shrank relatively little. Things like Trim and Molding glue shrink almost not at all.

Anyone interested in going back to the original (or at least, earlier) posts on it could probably find them on the Techniques forum. Maybe keywords like "shrink" "coke-bottle" and the like would work. Others than me probably know more about the details, but the difference in shrinkyness is easily demonstrable empirically.

Back to fins: any of these glues will work fine to hold them on, but I found that the joints I did with Titebond II double glue joints were (when dry) much more wiggly than visually identical joints I made with Elmers Carpenter's Wood glue. On one rocket (BT56 with Red Max shaped fins) I did with 2 fins being Titebond II, and 2 fins being done with the Elmers wood glue. The next day, so fully dry, and before any fillets were applied, if you held the rocket body tube tightly, you couldn't really wiggle back and forthe the Carpenters glue -joined fins, without risking ripping the underlying paper of the tube. The TBII fins could easily be wiggled back and forth. This went away after filletting (with TMTWG). This effect was explained to me in that the Carpenters glue shrinks more and sucks the fin down a bit. I reproduced this effect again on another rocket.

Not everyone has noticed this, so I've been meaning to try a side by side test with a fresh bottle of TBII. Maybe I had a wonky bottle.

Marc

As Mark II said, either one will work well, as will a number of other adhesives that bond wood and paper. In fact the cheapest elmers white glue will create a bond that is stronger than balsa or paper. Titebond and other yellow-brown glues may indeed be superior to white glues but if white glue will produce a bond that is stronger than the materials being bonded what's the point of stronger? Case in point, I had a hard landing with one of My Big Berthas at a recent launch, I broke two fins. The elmers white school I used to attach the fins never budged. That said I've recently yielded to peer presure and started using Titebond on my low power builds. I just want to be one of the cool kids.

Thanks so much for all this help! Great ideas and tips!