Cheap Fin hardening Techniques

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Const Star

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please provide some of ur best tips and products u use when reinforcing the strength of ur rocket fins.

some of mine are:

1. Thin layer of evenly spread wood glue

2. Wood glue spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe.

3. epoxy spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe
 
Orange Japanese tissue distributed by Peck Polymers.
Adhesive is Elmer's school glue gel.
 
Minwax wood hardener... just dip the fin in, or brush on. Be sure to sand the fin completerly to a 400 grit finish before applying as this stuff is difficult to sand.

NOTE: This stuff is MUST be used in a well ventilated area, preferably outside. It is full of all sorts of nasty flammable and brain cell -stomping chemicals. Please follow the aopplication instructions.

BTW: I alos dip balsa nosecones in Wood hardener for more durability.

Phred
 
Originally posted by astronboy
Minwax wood hardener... just dip the fin in, or brush on. Be sure to sand the fin completerly to a 400 grit finish before applying as this stuff is difficult to sand.

NOTE: This stuff is MUST be used in a well ventilated area, preferably outside. It is full of all sorts of nasty flammable and brain cell -stomping chemicals. Please follow the aopplication instructions.

BTW: I alos dip balsa nosecones in Wood hardener for more durability.

Phred

You don't have warping issues doing this? I did. I never tried it for nose cones though.

Nick
 
Hi Nick,

I have found the same warping difficulties as can be found with applying fill-n-finish. You cannot do one side at a time, or the fin will warp. That is why I suggest dipping the fin.

Ph
 
Thanks.

My newest method has been to use Modge-Podge and newspaper to cover. I do both sides and then place between wax paper and then under a book.

Nick
 
You are calling my middle name

Originally posted by Const Star
please provide some of ur best tips and products u use when reinforcing the strength of ur rocket fins.
some of mine are:
. . . . . . .
2. Wood glue spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper.


Why are you sanding away the paper?

I use watered-down Elmers and printer paper scraps. Sand the desired shape into the leading edges of your fins. Fold the paper (sharp crease) to fit the leading edge and cover both sides of the fin. Wet the fin with the glue, insert snugly into the folded paper, cover top & bottom with waxed paper, press under stack of phone books or magazines. When dry (a day later) trim off excess paper from trailing edges, root, and tip, and continue assembly.

The Minwax wood hardener also works well, but as astronboy has already noted, it STINKS (i.e., wife won't let you use it inside the house).

You can also use CA to wick into the end-grain and wipe all over the other fin surfaces (I use Q-tips to 'paint' the CA onto the balsa) but it stinks pretty well too. Use lots of ventilation, this stuff is not healthy for you.

I do not like to use 'just plain glue' to finish balsa. The water-based glues (Elmers, etc) may strengthen the balsa but they are usually not compatible with the paints. Unless you use a primer, the paint will craze at some point in the future, and all your finishing work will be wasted.
 
Originally posted by Const Star
please provide some of ur best tips and products u use when reinforcing the strength of ur rocket fins.

some of mine are:

1. Thin layer of evenly spread wood glue

2. Wood glue spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe.

3. epoxy spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe
If you plan to sand away the paper anyway, save time and energy and don't put it on to begin with. I.e. (1.) and (2.) above amount to the same thing, except (2.) involves more work. Adding paper will add strength, but only if it remains on the fin when you finish.
 
Another method is the CA approach. I found if you use the $0.99 junk from the bargain bin, and cut it 1:2 with acetone you get pretty good results.

Also, consider replacing the balsa with basswood. In a scratchbuilt the cost difference is marginal.
 
Originally posted by Const Star
please provide some of ur best tips and products u use when reinforcing the strength of ur rocket fins.

some of mine are:

1. Thin layer of evenly spread wood glue

2. Wood glue spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe.

3. epoxy spread evenly, followed by a sheet of paper pressed evenly and let dry. after its dry, sand away paper. and if needed, wet sand to get smoothe

regarding my wood glue and paper press method, works best if u use 2 books to flaten the fins and get glue even. i just tried it without it cause its still attached to the rocket itself (on the phoenix im restoring) and it was really un even and i had to sand off practically all the paper, and im even applying another stage of glue / paper to fix overly sanded parts. (excessive sanding on wood glue pulls it up) i bet this would work better with epoxy, but itd be more expensive and probably heavier
 
Originally posted by Const Star
regarding my wood glue and paper press method, works best if u use 2 books to flaten the fins and get glue even. i just tried it without it cause its still attached to the rocket itself (on the phoenix im restoring) and it was really un even and i had to sand off practically all the paper, and im even applying another stage of glue / paper to fix overly sanded parts. (excessive sanding on wood glue pulls it up) i bet this would work better with epoxy, but itd be more expensive and probably heavier
Best to even up the surface before covering it. Also, wood glue will sand better if it's allowed to dry for several days. If you sand it too soon, it's still kind of rubbery below the surface. Be sure to prepare the surface with sanding before applying glue, so it has a better chance to soak in and grip the fiber of the wood or paper. I like Fill-N-Finish for smoothing out balsa. Add little, if any, water, and do both sides of a fin at once. It's the fibers of the paper, glued to the surface, that add strength and smoothness. Sanding away the paper removes the advantage of adding it in the first place. I agree with others here that wood glue isn't the best way to strengthen balsa. CA (cyanoacrylate adhesives, such as Crazy Glue or Super Glue) soaked into the wood will strengthen it a good bit and seal it fairly well too, though it does become somewhat more brittle in the process. Finishing epoxy is good, but you're right that it's heavier. I like light paper for smoothness and strength. Experiment. Keep notes. Have fun. Share what you learn! :cool:
 
super glue would be another of those non cheap methods, and also, i dont like the fact it tends to crystalize and become britle in excessive amounts other than fixing broken glass figureins and such. epoxy would be my first choice for strength just due to the "thus far" experience i have. wood glue if used correctly and if u have patience is a nice choice. my biggest factor is finding a flattening method which allow me little or no sanding after its dried.

anywho, im getting some pics taken tonight of the Phoenix so far in the works. im pretty much done with all the sanding and i can basically paint it at anytime. i havent changed the engine mount at all yet, figured thatd be best waited til i buy the reloadable motor and make precise meaurements. i added some nose weight to it with a few sticks of hot glue. didnt have any clay stuff around, next best thing. also the nose cone fits a little loose, so i use a strip of tape to make it more snug for now.
 
Originally posted by Const Star
super glue would be another of those non cheap methods, and also, i dont like the fact it tends to crystalize and become britle in excessive amounts other than fixing broken glass figureins and such.
Yeah. If you just use it around the edges (except the root edge), you get most of the benefits with less cost. It also has less of the brittleness problem, since the rest of the fin isn't soaked and is behind the edge, absorbing the impact. This is what I usually do. I also use the CA (water-thin variety) to reinforce the ends of the body tube and the rear end of the motor mount, so they're less likely to take damage from shock cords and engine stuffing-in and removing. The paper or balsa swells a bit where the CA soaks in, so it means a bit of extra sanding in those areas (and for fin edges), but it's worth it, IMHO and not too expensive when done this way.

Originally posted by Const Star
Epoxy would be my first choice for strength just due to the "thus far" experience I have. wood glue if used correctly and if u have patience is a nice choice. my biggest factor is finding a flattening method which allow me little or no sanding after its dried.
I've not yet used epoxy in rocket construction, as wood glue is quite strong, and I've done only low-power to date. I plan to start my LOC Graduator over the holidays, and I'll use epoxy for that. Another reason I've not used epoxy on my fins is that it's heavy and expensive. Weight in the rear of a rocket is destabilizing, so I'd have to recheck stability, and so on. You can get epoxy glassy smooth though, so I'm sure I'll try it some time on a rocket that's big enough or long enough to get away with the added tail weight. Once a fin is relatively smooth and straight, papering it will cheaply strengthen and smooth it. I don't think I'd worry too much about sanding it first, unless it had noticable lumps or grooves in it. Maybe just a tiny bit to give the glue that much better hold. Balsa's pretty porous to begin with though. Once the paper's on properly and dry, the surface will be, well, paper smooth. :cool:

Originally posted by Const Star
I added some nose weight to it with a few sticks of hot glue. Didn't have any clay stuff around, next best thing. also the nose cone fits a little loose, so I use a strip of tape to make it more snug for now.
Tape is about the best way to snug up the nose, so I'd consider it a permanent solution if it was me. Quick, easy, good friction qualities, and it's adjustable to the tightness of the nose on any given flying day. Temperature and humidity can alter the fit. For nose weight, epoxy clay is probably ideal, though pricy. Regular modeling clay can be stuffed in and covered with a layer of wood glue or white glue for a bond that will last decades. Ordinary epoxy, if available, is heavy enough and self adhering. If you need more weight in less space, small lead fishing weights can be dropped into the liquid epoxy before it begins to set. They'll sink to the tip of the inverted nose, giving you maximal stability for the weight. I would think that in most low power cases, you could do that with hot glue too, but in higher power boosts, the weights might pull through the rubbery glue.
 
annother easy way is adhesive label paper, the kind that sticks like crazy, than I just add a little filler to smooth things up.
quick and easy.
 
i've heard (but never tried) of laminating them with that peel and stick lamination. and then epoxy the fillets over the bottom of the laminate.
 
Originally posted by stymye
annother easy way is adhesive label paper, the kind that sticks like crazy, than I just add a little filler to smooth things up.
quick and easy.
I'm always concerned that I'll get the stuff on wrong and not be able to pull it away to adjust it properly. I guess if I put it on before attaching the fins. it would be easy to trim it to fix anything except wrinkles.

Do you paper it then smooth it or smooth it then paper it? Sounds like the former. I can see advantages to both. Paper attached directly to the balsa is likely to adhere better than if it was attached to a layer of Fill-N-Finish (or simlar), but papering last ought to give the smoothest finish.
 
ive forgot how to spell the word so please no laughing

But has anyone tried polying the fins with a pretty good coat of polyeurethane < dunno how its spelled so sound it out. i used to used this stuff when i worked on house redoing floors. leaves a nice hard glasslike coat. im considering brushing some of this stuff on rockets as a good strengthener, fins, body, etc. ive got tons of the stuff too so its cheap for me to do. of course the fumes are killer
 
many ways to strengthen the fins and
almost any finishing product would work , just depends on how heavy the rocket can be yet still acheive the results your after.

obviously on model rockets it's best to build light
 
true, do u think it would be a good method for a extremely high powered rocket? thats like really huge? cause at that level it would (in my theory) add a optimal amount of strength and in ratio wouldnt hardly add any weight.
 
Const Star,
You are right that you can add a lot of strength for not very much weight.
About the only time you need to be cautious about reinforcing fins (or switching up to materials like basswood or plywood) is if the fins are relatively big, or if you start out with a design without much stability margin, or if the rocket is already heavy and performing poorly.
Most of the time you can reinforce fins and not hurt stability much at all, and the performance difference would be barely noticeable.
But any time you modify someone else's design, especially when you add any weight in the back end, you really need to re-check stability (statement of the obvious?)

For 'really high-powered rockets' I am going to let the expert builders here on TRF answer that one. I think they commonly use plywood or fiberglass for the basic fin, and often cover with more fiberglass and epoxy. It seems to be the required minimum?

BTW, as far as doing a low-cost CA treatment on the balsa fins, I buy the little CA tubes at the dollar store as my main source. (Yeah, I know, some of you are screaming in horror out there---)
I get the cards with three little tubes for a buck, sometimes five tubes, and it only takes one or two tubes to do the fins for one rocket. I think that's pretty cheap.
 
mind explaining what CA is? i know im probably getting alot of looks right about now from people wondering why i dont know what CA is. but level with me i dont even go to shows nor have i since i was a little kid = (
 
superglue, crazy glue....etc...ZAP CA glue...it stands for cyanoacrylate. ZAP is the good stuff, IMO. i've glued my thumb and index finger together by accident and the only reason they came apart was because i had the ZAP release stuff. heh. now i wear gloves.
 
o ok, they sell that stuff in my mueller magazine. best stuff for replacing cue tips and what not.
 
most drug stores have them...like CVS, walgreens...wal mart also has super glue and crazy glue. home depot...etc...home depot also has quite an extensive variety of other glues as well.
 
Seems like to an extent this thread has gone from a strengthening thread to a smoothing thread. Judging from previous posts by Const Star, I'm guessing the question is one of strengthening the back fins of an Estes Phoenix. For that purpose, having seen Stones launch and repair his a number of times, I'm convinced that a light layer of glass is the only way to go to guarantee strength.

Any adhesive and/or treatment coating on its own provides a small amount of stiffness helping to prevent cracks along the grain, but will never provide considerable structural strength to resist an impact break that would go cross-grain without the coating. This is why people vacuum bag their glassing/carbon works--the epoxy doesn't provide the strength, the cloth does.
 
hate to break the news to ya, but it provies the key element in strength. and this thread didnt go from a hardening to smoothing thread, because all about the same thing. no one wants to harden their rocket stuff and keep it looking like a turd or something. its all in the process of crafting a good rocket. and the glass coating thing im sure is very strong, but theres a million other things u can do as well. so it aint the ONLY option as far as strength goes. might be ur decided option. id like to see u try and break a good coat of poly coated fins. weve dropped refrigerators on the stuff and only see slight scratching. couldnt crack it or damage the wood under it.
 
Regarding the strengths of hardners/adhesives like epoxy or polyuerethane and glass fiber, you're essentially both right. Epoxies and resins are good in compression--like when you drop a refrigerator on them. They're not so good in tension, though.

Glass fiber is really good in tension--you can pull on it and it won't break. Together, glass and epoxy make a really good combination.

Do a test. Coat a one foot section of your favorite fin material in poly or epoxy or both. Allow to set. Now bend it. One side of the material is in compression and the other is in tension. See which side cracks. Repeat with glass fiber and epoxy and see what happens.

This is exactly why engineers use steel to reinforce concrete. Concrete is great in compression, but it doesn't do very well in tension, like when a concrete beam bends. Steel needs help in compression because of it flexibility. That why they add steel to the bottom of a reinforced concrete beam.
 
Getting a little closer to the thread's start, I like to use thin layers of quality thin CA (Zap, Bob Smith/Store brand), followed by 400 grit, then 600 grit wet sanding (a final dry 600 grit once over really kicks it up). This can yield a smooth as glass surface.

A few cautions are in order-- this can only be done in a well ventilated area, and (need I add) you must use extreme caution when applying CA, as you can easily end up gluing your finger (or anything around) to the fin which is quite a mess. But with patience and caution, you can get really nice results.

Taking this a bit off topic, I am looking for an easier way to harden and smooth balsa nose cones. I have yet to get a Tyvek (or paper) to reinforce under a light coat of epoxy that fits properly without wrinkles or lines. I use the CA method and follow with light epoxy and allow it to drip pointy end down, but this is still all too subject to puncture or dent. Does anybody have a better way to do this yet?
 

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