Edge joining balsa

[DJ Delorie]

For an upcoming model, I need to cut fins from balsa sheets wider than 4" (around 6.5"). Any tips on edge-gluing two sheets together to make wider sheets, without having the seam show through the paint?

 

[DPatell]

hmm...I worked on a plane in my tech class and we needed to join pieces together. I would suggest sanding the edged you wish to glue at 45 degree angles, then joining them with wood glue. Then, place wax paper on both sides and put the joint under a stack of books. That should provide a nice, invisible joint, if not then wood glue is sandable.

The other nice thing about the joint is that it is now the strongest point in the board. The actual wood will breakbefore the glue does.

 

[Silverleaf]

Your best bet MIGHT be to use epoxy to glue the edges together, and then after cutting each to the proper size, fiberglass them. It would add strength and give them a solid structure.

Ray Dunakin posted a thread on repairing a fin edge - so the same technique would work for this process.

https://www.rocketryforum.com/showthread.php?s=&threadid=5633

In another thread, he had a photo posted to his Epson Photocenter that shows what the finished fin repair looks like. Here is the link - the pic in question is at the botom:

https://albums.photo.epson.com/j/AlbumIndex?u=3009006&a=30098271&f=0

Hope that helps,

 

[DJ Delorie]

This will be for a large solar sailer, so both end grain edges will be braced (one end will be the root, the other will have the dowel glued along it) so I'm not worried about strength or shredding, just appearance.

 

[OKTurbo]

The way I've always done this is to sand each joining edge straight using a long T-bar sander. Place both pieces over a sheet of waxed paper, then use thin CA glue to join them. Make sure the edges are flat against your building board. I usually press the two pieces together to prevent any gaps. The thin CA will wick right in and Voila!

A little sanding on the surface with the T-bar to smooth out any bumps and you're set. Fill....Prime....Paint...and you'll never know it's there.

 

[Micromeister]

Carpenter John has to agree wth dan on this one: 45ing the edges increased the joining surfaces making for a stronger butt joint. Wax paper and weighting the work sheet will indeed make for a great sandable joint, which will require some addition sanding to become invisible.

You can square edge join balsa sheets as well. either method should use the double glue joint method.

1. Apply a good bead of yellow carpenters glue to one of the joining edges.
2. On wax paper join the two parts, squeezing the parts together in a side to side slipping action until you can feel wood to wood contact. whip off excess glue.
3. Seperate the two parts just joined and allow the glue to dry (10 to 20 minutes). I usually elevate the parts on a book or something to ensure all wood surfaces remain clear of glue build-ups. When these glued parts feel completely dry move on to step 4.
4. Apply a second bead of glue to one of the joining parts and repeat step one, squeezing out all the excess glue in the side to side slip action until you again feel wood to wood contact.
5. Wipe way excess glue, cover with a second piece of wax paper and weight with a couple books or other heavy object.
6. If using Carpenters wood or elmor's glue allow the joint to cure overnight.
7. Once fully cured a double glue joint is Stonger than the balsa wood itself.

I would also recommend Ambroid Cement for this type balsa to balsa joint using the same method. This cement sets up faster then either carpenters or elmor's white glue. it is formulated to remain flexable even after years. Model airplane flyier have swarn by this stuff. I can attest to its great stength and longevity.

I would NOT recommend Epoxy for this application, Epoxy becomes brittle very sortly after applicaton.
Hope this helps

 

[jflis]

You may wish to look into cutting a "key" in the edges to be joined, if you have enough stock to do so. I've attached an image of how I repaired some damange on a model I am working on. You can read the whole thread about this design and this repair here:
https://www.rocketryforum.com/showthread.php?s=&threadid=1486&highlight=proto

 

[DJ Delorie]

You may wish to look into cutting a "key" in the edges to be joined,

If I were joinging the ends, that would help a lot. For edge joining, that makes the joint weaker. At least, with woodworking projects it would.
I don't suppose you plan on carrying 8" WIDE balsa sheets any time soon, Jim? ;-)

And before anyone asks, yes, I thought about plywood. Too heavy and the extra strength shouldn't be needed.

 

[OKTurbo]

Wow...you guys make this complicated. A 45deg bevel joint would be great, but you'll have to be careful making the joint or it will end up crooked.

A 90deg butt has always worked for me. Another thing I do is (if the wood is thick enough) is to poke some holes on the joint surface with a pin. This gives the glue a little more surface area and grip.

CA is quick and simple, but I've also used Ambroid and Sigment. I'm partial to SigMent. SigMent thins nicely using Acetone for those indoor FF projects. About the only guys who use Ambroid anymore are the free flight and indoor model airplane fliers. (It's fun peeling the glue off your fingers all night long...)

I guess it boils down to what works for you, and how much patience you have.

Here's a picture of the joint on my big Red Max. 3/16" balsa fins.

 

[OKTurbo]

Here's the final product...

No failures yet. Flown half a dozen times on AT F21's. It starting to get a few "battle scars", but it's solid as a rock.

 

[Micromeister]

No we are not making anything difficult but we are trying to give folks good info.
Good grief OKTurbo! CA is an awful choice for edge joining, it's even worse then eooxy. Not only does the CA become brittly as it sets..we didn't use accererator did we.. that just weakens the CA further. and the wicking mentioned makes the Balsa brittle as well, inflexiable and subject to easy damage..Super BAD choice folks don't do it!.
CA a is great for competition models that will only be around a very short time, spot glue-ups, fixture holding and some other things. I use CA extensively but NOT for critical joints.
Butt jointing any wood can be done with a good square edge,(45'ed edges are better but more time consuming) plain Old Every day Elmor's white glue is a better choice than CA, though not much, Yellow carpenters glue, Ambriod, or Sigment are EXCELLENT choices for this type bonded joints. Strength and flexibitly is what we looking for in edge joined wide width flat thin slabs.
Kind of keep in mind NO one adhesive, glue or cement is correct for every joining job, they all have there place and purpose. Oh darn something else to research and learn about?? What's the difference between Adhesives, glues and cements? Learn something new everyday
Hope this helps.

 

[OKTurbo]

Whoa there...I meant no offense. Use what you're comfortable with. I'm sorry for the "complicated" comment. It was meant in jest.

In my experience, I've had no problems at all using CA to edge join balsa. I won't disagree that there are better ways to do it, but we're not talking rocket science here....well....maybe we are.

I didn't want to start an argument. I just wanted to share my experience. I've used this method on model rockets and R/C airplanes over the last few decades. I use Sigment or Ambroid on my indoor and outdoor free flight airplanes.

I've never had a failure of an edge joined component...be it a rocket fin...or a vertical stab...or a rudder...or whatever... due to the joint coming apart. If they've crashed, then the damage was much more than any joint could handle.

I wouldn't say the CA is a "Bad" choice. It's may not be the best, but certainly not bad.

I would never recommend something that I hadn't done myself. It may be a "bodge", but it's worked for me. Maybe I've just been lucky.....a lot.

John

 

[Stymye]

I like yellow glue for edge joining,,because no matter how good you get the joint,a little flat sanding is usually needed..

cya and epoxy are considerably harder than wood glue so when you flat sand the joint the balsa surrounding the joint gets worn away too easily leaving a ridge,,,of course nothing that a little (or alot of)filler wont fix...lol

If you look at ok turbo's first pic you can see the obvious area of hardened glue,,
with yellow glue and a wipe with a damp napkin ,, once dry,,you would hardly notice the joint,,of course no wrong way to do it really in my opinion...... just a matter of personel preference

 

[sandman]

The biggest problem with edge glueing balsa is sanding across the joint to get the glued edge invisable.

You always seem to get a visable "hump" if you're not very careful.

As for glue...well you guys should know me by now...Elmer's white glue all the way. Balsa is pretty weak by itself. Almost any glue joint will be stronger than the sorrounding wood.

OK, I do have to agree with Micro. CA glue sprayed with an accelerator is one of the weakest glue joints you can use.

sandman

 

[Silverleaf]

I really love Great Planes Wood Glue with Aliphatic resin. Super strong, cleans up easily, and has a scent that I don't mind. Not to say I sit and smell the glue all day long, but I know I'm working with a quality glue.

8)

 

[Micromeister]

Originally posted by OKTurbo
Whoa there...I meant no offense. Use what you're comfortable with. I'm sorry for the "complicated" comment. It was meant in jest.

>>>>OT, No offense taken. Nor am I going to argue about weather one can or can not use CA in edge jointing, one could use chewing gum. However DJ is about to do something he hasn't done before and wants help with the best method & materials for the job. Your " complicated" comment just didn't fit the request, and your choice of materials was way flawed. I am stating as clearly as can be done in the Typed world of computers CA isn't the adhesive to be used in this case..PLEASE DON'T DO IT. Any or the aliphatic resin carpenters (Yellow) glues (Elmor's, Great Planes or whoevers) is the best choice Glue for this Joint. This is the help DJ asked for.

>>>>DJ don't forget the double glue joint method, wadding thou all these distractions no mater which glue you use (except CA) the dryed double glue joint will be stronger than the balsa wood itself. Waxed paper both sides and multi booK weighting will help keep the slab(s) flat while drying overnight.

I wouldn't say the CA is a "Bad" choice. It's may not be the best, but certainly not bad.

>>>>As I said it is not a bad choice.. it a SUPER BAD choice..please don't teach others bad modeling habbits CA has no business being used in this type application. As was explained in the eailer post.

I would never recommend something that I hadn't done myself. It may be a "bodge", but it's worked for me. Maybe I've just been lucky.....a lot.

>>>>>Yes; you certainly have been lucky and maybe a lot. This is exactly why I love this forum. We can exchange "experiences" and Learn what we've been doing that could (should) be done differently to make our models better, safer, longer lasting. Sometimes it's hard to hear, but sometimes we also have to learn from our experiments or mistakes. OBTW sometimes crossover experiences are of little help. Stresses on model rockets are far different then those on freeflight R/C or even static line model aircraft. Lets' try to give folks the BEST methods and materials for a given task.
For sure express your experiences, we all want to hear what everyone else is doing but if we find others have a better way, more "experience" or better info on a method or material saying ha! this is a better way, or try this method for stronger results.. with some explaination as to why it's better then take it for what it's worth, Good advise. The more we learn the better our modeling will be. That's what I ment by "let's give folks good info."

Hope this is taken in the good spirit of passing along knowledge.

Fine looking fillets on your Big Red Max OT, good job

The 15" wings on this Bomarc 1:13.25 Scale are 3/16" edge glued balsa just at the prob tips horizontially across the span. This slabs are 45 degree butt joints with ambroid cement. Sorry I don't have anything closer, but the seam is completely invisible on very close inspection.

 

[Fore Check]

This is an interesting "discussion."

I've had no trouble whatsoever using CA. I use the thick, "slow" CA on almost everything that doesn't otherwise require epoxy.

Too bad I don't have pictures uploaded of my Attack Craft Orion (Estes kit.) It has some rather large fins that are all glued to each other (a whole mess of end-type joints, if you will.) I've launched it several times, and it has survived with barely a scratch - even after a C6-5 launch to over 1000 ft and a melted parachute (so a big plummet and a *hard* landing). I'll take some pictures of it when my wife gets home with the camera later.

It's hard to visualize what I'm talking about as far as all the fins glued to each other by looking at the catalog pic (no plans on the internet) unless you've actually seen one built.

There are 6 "fins", but only two of them are attached to the body tube. The ones attached to the body tube have a root edge about 3.5" long and the fin is a strip about 1/4" wide. These are mounted across from each other on the airframe (horizontally.) Then, there are two large "delta" type fins that are glued to the edge of those strip fins, but angled downward at about 30 degrees. Then there are two smaller delta fins glued to the top of the large set of delta fins at a right angle (so they each end up being about 30 degrees from vertical.)

Again, mine are all glued together with thick CA and it seems to be quite rugged. The joints, sanded and sealed with aerosol sanding sealer, look pretty good to me.

Like I said, I need to take some pics and get them uploaded.

But back to the topic of the thread - yellow glues may be the "best" choice, but I've had no trouble at all using thick CA either. I guess I've been "lucky" too....

 

[Stymye]

give it time ,, on some of my old cya-glued rockets, the joints have become quite brittle with age..they are since retired anyway

I don't recall what cya I used ,but it was most likely superglue from the little tubes,mabey a thicker or better brand will last longer

I don't think you will see Norm Abram using cya or epoxy for wood
and he can afford what ever he wants

what better choice for glueing wood to wood than Wood glue?
it's a no-brainer,,,but whatever works for the builder is the right choice in the end