CA and balsa nose cones

[AfterBurners]

Well I'm a believer now. I never tried this method of sealing a balsa nose cone, but I must say I'm impressed. I had a nose cone that I didn't use for my Bat Ray (BT-70) due to some major imperfections and decided to use it on a scratch build. Just your basic 3FNC. I epoxied the nose cone into 4" of body tube and sanded it to shape and even the out the OD with the OD of the body tube. I used a tube coupler to make a shoulder and some balsa for a bulk head and attachment point.

After I got it shaped and sanded I applied some thin CA (BSI was all I had) and I wiped it evenly using a paper towel. I came back and sanded it with some 220 and repeated the CA, but then came back with some 320. After the first coat of primer there were only a few areas that needed attention so I used some thin out FnF and sanded and primed again. I applied one more coat of gray primer and wet sanded the nose cone. The results are below. It blended nicely and now it's ready for paint. I used 30 minute epoxy for the engine mount and applied a coat to create a fillet on the AFT center ring. The epoxied "Flowed Out" and coated the entire AFT ring. It feels like glass and I like the results.

 

[luke strawwalker]

Nice work...

I really like using that method... it won't necessarily make the cone bulletproof (though it DOES toughen up the outer layers somewhat) but it REALLY makes it possible to get the cone looking as smooth or smoother than a plastic cone when you're done... I do this on ALL my balsa cones and transitions... works great!

Later! OL JR

PS... any 'brand' CA works fine so long as it's "water thin" or "ultra thin" kind so it can soak into the wood... also be sure you do it outside so the fumes from the CA curing don't get you as it's applied!

 

[AfterBurners]

Thanks JR - I'll get some pictures up when the rocket is done. Should be soon I hope.

 

[Marc_G]

Nice work.

I love this method. I do it for all my balsa cones and similar parts. Just did the first step on two last night, actually!

A related technique I've learned is that if you have a cone with spiral score marks, as in it didn't get sanded quite right on the lathe, is to do a first coat of thin CA, lightly sand it, and use medium thickness CA for a second coat. The medium CA flows just enough to fill most of the typical score marks like this. A little sanding and you'll be at a point where a tiny bit of spot putty or even heavy coats of filler primer will give you a perfectly smooth cone. I'm more successful with this method than pre-smoothing the cone before CA... I tend to deform them if I sand before hardening with CA.

Marc

 

[majordude]

Is there a link to an original thread or technique? This is all new to me. I have always had problems trying to fill in the pits of wooden nose cones.

 

[luke strawwalker]

https://www.rocketryforum.com/showthread.php?29228-Dr-Zooch-Rockets-EFT-1-beta-build

Specifically pics and description of the process at about Post 15 and on...

https://www.rocketryforum.com/showt...-Rockets-EFT-1-beta-build&p=261802#post261802

Also in this thread, starting about post number 6...

https://www.rocketryforum.com/showthread.php?25443-Dr-Zooch-SLS-beta-build-thread

Lots of pics and text in those for you... and other helpful hints...

Later and hope this helps! OL JR

PS... I see those are more about "damp sanding" than actually having any pics of the CA hardening techniques, even though that's the first step I do on balsa cones and transitions I get in kits...

Basically, you want to use WATER THIN CA; Hobby Lobby sells it in a pink bottle labeled "Ultra-Thin" CA... it works very well and it's cheap. Get small bottles-- CA tends to thicken and go bad over time, so don't buy a huge bottle for big bucks and have it go south on you. If you have a local hobby shop, they'll probably have a "house brand" CA, look for the "water thin" or "ultra-thin" stuff...

Take your nosecone or transition OUTSIDE to apply the CA... I hold it between two fingers by the very back of the cone or transition shoulder, and using the tip of the bottle as an 'applicator", I gently squeeze out some CA onto the surface of the cone JUST AHEAD of the shoulder-- DO NOT apply it to the cone shoulder unless you want to have to sand the cone back down to size, because it WILL increase the diameter of the cone just enough to make it either a very tight fit in the tube, or impossible to get into the tube without sanding it down quite a bit. Allow the wood to "drink in" as much CA as it can possibly take-- I gently turn the cone between my fingers as I apply it, and gently spread it out over the surface of the cone using the flat side of the bottle tip applicator... try not to stick the very tip hole of the CA bottle against the wood, as you may "suck in" debris that will eventually thicken and ruin your CA. Work evenly across the surface from the back of the cone toward the front, until it's evenly covered-- keep applying it til it starts to run down the cone and drip off at the tip, basically... (or about to drip). The CA will be drawn by capillary action down into the grain of the wood, where it will cure inside the wood grain and pores, turning the balsa cone into a simple "composite" material, consisting of wood fibers and CA resins, sorta like fiberglass or carbon composite materials that consist of fiberglass fibers or carbon fiber locked inside epoxy or polyester resins... BE CAREFUL NOT TO GLUE THE CONE TO YOUR FINGERS, because the CA WILL wick back through the balsa grain to the base of the cone where you're holding it-- keep turning it and don't hold it tightly or steadily or you WILL glue the cone to your fingers... if in doubt, use nitrile gloves to hold the cone. When you're done applying the CA and it won't soak up any more, set the cone aside on a piece of wax paper-- this will prevent it from gluing itself to whatever it's sitting on!

ALSO, BEWARE OF THE FUMES! CA gives off some powerful ammonia-like fumes as it cures, ESPECIALLY in large amounts like this... BE SURE you do this OUTSIDE, and preferably in a well-ventilated place with some moving air currents... try to be CROSSWIND from the part... if you're upwind, the fumes will blow in your face from the part... if downwind, the air currents swirling around you can whiff it up into your face. Crosswind should carry the fumes to your right or left and away from you...

Good luck!

 

[powderburner]

For small balsa NCs, I have had good luck using those little tubes of "dollar store" CA to harden the balsa surface.

Also, you may want to try Minwax wood hardener... but it is also pretty smelly, best used outdoors.

 

[majordude]

Good luck!

Awesome explanation! THANK YOU!

I take it that the glue hardens by itself in a few seconds/minutes? Do you sand it afterwards or add another layer of CA to make sure you fill in all the pits?

Do you do this on plywood fins too?

 

[modeltrains]

For small balsa NCs, I have had good luck using those little tubes of "dollar store" CA to harden the balsa surface.
Also, you may want to try Minwax wood hardener... but it is also pretty smelly, best used outdoors.

Have tried each of those and can verify they work. Was unaware of the wood hardener until seeing it on here somewhere a a year or two ago.
Have used the CA over that Elmer's carpenters wood filler, still works fine. Before learning of wood hardener something I did was saturate balsa with Minwax clear gloss lacquer - and you wanna talk about something smelly that you'd better do outdoors and stand upwind of - yikes that lacquer is potent! But had already learned that lacquer is potent thing about four decades back. Also tried shellac, it works reasonably and is dramatically less potent since its solvent is alcohol. For the boatbuilders and cabinet makers there are shellac flakes you can buy to mix yourself to whatever viscosity desired, and idea not tried yet.

 

[modeltrains]

ALSO, BEWARE OF THE FUMES! CA gives off some powerful ammonia-like fumes as it cures, ESPECIALLY in large amounts like this...

He ain't kiddin, that vapors from that stuff can seriously mess with the soft wet tissue in your eyes and the slimy wet tissue in your breathing parts.

 

[Marc_G]

Awesome explanation! THANK YOU!

I take it that the glue hardens by itself in a few seconds/minutes? Do you sand it afterwards or add another layer of CA to make sure you fill in all the pits?

Do you do this on plywood fins too?

My technique: do a first coat with thin CA, pretty much like JR says. I let it harden an hour (probably overkill) then hit the cone with a 220 sanding sponge to remove the hardened hairs and such. Then I like to do a second coat with either thin CA using a q-tip to spread it around, or If the balsa seems like it has a lot of little pinholes, I switch it up to medium CA at this point instead of thin, which tend to do a better job of filling the pinholes.

Ply and basswood tend not to benefit as much from CA treatment as they are already harder and less grainy (Easier to fill) than balsa. Just my 2 cents.

 

[luke strawwalker]

Also, you may want to try Minwax wood hardener... but it is also pretty smelly, best used outdoors.

... And takes FOREVER to harden up and fully cure, and in the end the "toughening" is really no better than you'd get from a CA hardening treatment that's done from gathering materials to finish rough sanding in less than an hour...

Just sayin'... Later! OL JR

 

[luke strawwalker]

Awesome explanation! THANK YOU!

I take it that the glue hardens by itself in a few seconds/minutes? Do you sand it afterwards or add another layer of CA to make sure you fill in all the pits?

Do you do this on plywood fins too?

CA won't really "fill in" the pores in the wood, not and get it glassy smooth like a filler would... the purpose of the CA is really to "toughen up" and seal off the wood grain... the CA soaks into the wood and fills up the pores, but it still leaves the surface rather rough... To get it looking nice, you really need to brush on a coat of Elmer's Carpenter's Wood Filler (the "creamy" style, not the "chunky" looking stuff that has glass beads and wood dust and crap in it-- that stuff sands like rocks-- it's just terrible... the "good stuff" looks basically like smooth peanut butter when you open the tub or tube...) Put a spoon-size dollop of CWF into a small resealable bowl or jar (baby food jars work great for this, and they're cheap... or the little resealable bowls the side orders come in from KFC). Put a few big drops of water in there, and using a 1 inch paintbrush with fairly stiff bristles, "work" the water into the filler by "dabbing" the brush against the filler and rubbing it with the bristles... after a few minutes you'll see the filler getting thinner... if it's still thick like pancake batter or something, add a few more drops of water and work that in... you're shooting for the consistency of hot dog mustard... thin, but not TOO thin... brush it on the nosecone from just above the shoulder to the tip all the way around... (I usually tape over the shoulder of the cone that goes into the end of the tube with a wrap or two of masking tape to make sure) Allow to dry thorougly (usually about an hour or so) and then sand it down with 220 grit followed by 400 grit...

The cone will be VERY smooth after this... inspect for any dings or spots not fully filled, and if needed, brush a little more on, allow to dry, and sand smooth again... it's not ready to prime and then finish sand as previously described in another post...

Using the "water thin" CA that I use, it goes on and you can literally SEE it being "sucked into" the wood like water into a sponge... Balsa wood is shot though with pore spaces and holes, which is why it's SO lightweight... the CA, due to capillary action and the low viscosity, will be "sucked into" the wood... CA cures by reacting with moisture to cause it to "set up" and cure... CA can cure almost instantly... in fact, the chemical reaction as CA cures releases heat (endothermic reaction) and can get quite HOT from curing very fast... and I've seen balsa parts that had too much moisture inside the wood literally SMOKE or STEAM from the heat of the CA kicking off... When hardening parts with CA, you keep applying it until the wood simply won't suck in any more... when it starts to run down the nosecone or transition to the tip and drip off, it's had all it will take.

Now at this point, you've got a cone covered with wet CA that won't soak in... if you're REALLY QUICK and use VERY LIGHT PRESSURE, you can wipe the excess CA off-- BUT DON'T GLUE THE PAPER TOWEL TO THE CONE! Usually this isn't necessary and so I don't do it. If you've already installed the screw eye into the cone, you can hang the cone up vertically to allow the CA to dry. If you haven't, set the cone point up on a piece of wax paper to dry... some CA will migrate down from inside the cone and CAN glue the cone to the cardboard box or whatever you set it down on if you DON'T use a piece of wax paper... (ask me how I know this!) Give the cone about 10-15 minutes and the CA should be fully cured and "dry"... the cone is now ready for sanding it down with 220 grit... CA tends to raise the balsa "hairs" (bits of wood fiber on the surface loosened when the cone is sanded to size and shape at the factory) and bits of balsa dust embedded in the surface of the cone... these combine with CA to form a hard "gritty" surface on the balsa after CA hardening it... sanding with 220 grit will take this off and make the cone smooth-- generally you'll want to brush on CWF and then sand that down, which will smooth the cone out completely and make it look just like a plastic cone after it's primed and sanded...

Plywood fins... I suppose you COULD do this to plywood fins, but there's really no need and I can't see anything to be gained from it... plywood for models is usually birch or other woods that are harder and denser than balsa is, and thus there's little/no pore space for CA to soak into, and little hardening will occur... BALSA fins, on the other hand, have a LOT of open pore space inside (again because balsa is a very light wood) and the CA CAN soak into them and help harden them up...

Later and hope this helps! OL JR