Launch Lugs and air bubbles

[accooper]

Anyone have a great idea on how to keep from getting air bubbles in the launch lug fillets? I have tried everything I know with little or no luck.

Andrew From Texas

 

[WillMarchant]

I try to force the glue as deeply into the body-tube/launch-lug joint as possible.

If you see bubbles early on in the drying process you can try to pierce them with a pin. Sometimes that will let the bubble "heal."

 

[NjCo]

Try using Titebond Molding and Trim Wood Glue. From what I can tell this is the same thing as the other Titebond products but it dries clear and doesn't run. It doesn't run because it's very thick stuff and that's just the key to those tight spaces around launch lugs. Because the glue flows slowly it's easier to get the glue into the crease along the launch lug without getting a huge glob of glue in the area. Works great on fins as well.

 

[hcmbanjo]

Try popping the bubble with a toothpick instead of a pin or hobby knife.
With a very sharp point you'll "chase" the bubble around without popping it.
The blunt tip of a toothpick will pop it usually the first time.

Popping the lug air bubbles is best done when the glue is fairly wet. The glue will flow into the area where the bubble was. Sometimes you'll have to fillet three times to get a smooth fillet on a launch lug.

 

[Boosterdude]

The best way is to stop using wood glue and using some 30 minute epoxy mixed with micro-balloons. You can make a much better fillet without the worry of the air bubbles. Very light weight since you're using very little epoxy.

 

[SteveF]

second on the tite-bond molding & trim glue - stuff is incredible for fillets

 

[accooper]

I tried this on an old piece of bt-60 and a launch lug.

I took some wood filler, added just enough water to make it like cake frosting, put it in a zip lock bag, cut a very small hole in one corner of the bag, and squeezed gently just like I was using glue to make a fillet. It takes a while to dry, but then I sanded it with very fine sand paper and it looks great. If I knew how to affix a picture with this I'd show you how it looks.

Andrew From Texas

 

[RimfireJim]

I tried this on an old piece of bt-60 and a launch lug.

I took some wood filler, added just enough water to make it like cake frosting, put it in a zip lock bag, cut a very small hole in one corner of the bag, and squeezed gently just like I was using glue to make a fillet. It takes a while to dry, but then I sanded it with very fine sand paper and it looks great. If I knew how to affix a picture with this I'd show you how it looks.

Andrew From Texas

The disadvantage of that method is that the wood filler doesn't add any strength to the joint, whereas using glue does.
I haven't tried the trim glue others have mentioned, but I found Aleene's Tacky Glue works for me. I suspect they are similar: high viscosity polyvinyl acetate (PVA) glues. I use it for fin and launch lug fillets on my LPR birds.

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[MarkII]

Wood filler can be used to make smooth fillets, but it won't add anything to the strength of the joint. Epoxy mixed with microballoons, as Boosterdude suggested, works very well, especially because the fillet can be sanded smooth afterward. If you are going to swipe an epoxy fillet smooth, though, put on a nitrile glove first; don't swipe it with an unprotected finger. But it is tricky to sand fillets for something as small as a launch lug, and mixing up a batch of epoxy just for the lug is a bit of work for just a little part. Air bubbles come from getting air trapped in the joint as you place and position the lug. Putting a thick bead of glue on the tube (as opposed to the side of the lug), and then pressing the lug down solidly, sliding it around very slightly to give it solid contact, and then swiping the sides of the joint clean with your finger immediately afterward can help lessen the chance that you will get air bubbles around the joint. Also, using a glue that has a smooth but thick consistency with a lot of solids, such as Titebond Molding & Trim Glue or Aleen's Thick Designer Tacky Glue (in the white plastic jar with the pink label) will also work well. (But be sure to swipe the fillets smooth immediately after application, because both glues set up fast.) Titebond M&T Glue is similar in appearance to, but is not the same as, its wood glues. Aleen's Thick Designer Tacky Glue is a type of white glue that is VERY thick in consistency. (Too thick to use in a squeeze-type bottle, in fact.) You can find it at a crafts store, such as Michael's, or in the sewing and crafts section at Walmart. Using these types of glue is similar to using the epoxy+microballoons mix, except that they can be used right out of the bottle or jar and don't require mixing beforehand.

MarkII

 

[Evo666]

I check it every so often when drying and pop it with a toothpick.

 

[accooper]

OK, here is what I did. I glued on the launch lug as usual, using wood glue. Put fillets on the lug, twice as usual. Then after that was good and cured, then I used the wood filler over the wood glue.

Hope this clears up what I did.

Thanks for the input.

Andrew

 

[luke strawwalker]

Anyone have a great idea on how to keep from getting air bubbles in the launch lug fillets? I have tried everything I know with little or no luck.

Andrew From Texas

Use Titebond Moulding and Trim Glue (TMTG)-- the stuff is great! Goes on smooth and slick, and it's thicker than regular white glue so it WILL NOT RUN around the ends of the launch lugs-- it stays where you put it and doesn't form bubbles or shrink anywhere near as much as regular white or yellow glue as it dries.

I usually use a double-glue joint with yellow glue to put the lug on the body of the rocket (since I usually use double-lugs, a shorter one 'up front' and a second in a fin fillet) and then after they've dried go back and fillet the lugs with TMTG. When it's done it looks every bit as good as epoxy fillets with none of the epoxy hassles or weight. The TMTG makes killer fin fillets as well...

Highly recommend it! OL JR

 

[luke strawwalker]

OK, here is what I did. I glued on the launch lug as usual, using wood glue. Put fillets on the lug, twice as usual. Then after that was good and cured, then I used the wood filler over the wood glue.

Hope this clears up what I did.

Thanks for the input.

Andrew

I've never had to fillet twice with TMTG... OL JR

 

[accooper]

Where can you get this glue?

Andrew

 

[luke strawwalker]

Where can you get this glue?

Andrew

Lowe's or most better hardware stores... read a post recently that said Home Depot didn't carry it, but I'm not sure... if they don't they're kinda falling down on the job!

It's in a gray bottle right beside the Titebond and Elmer's yellow wood glues... Pic below to help...

Later! OL JR

 

[Pem Tech]

I use epoxy for mirror smooth LL fillets, or Apoxy clay, which is heavy but works well. The advantage of Apoxy clay is that it has a long pot life and can be molded and shaped.
:cyclops:

 

[kjohnson]

I've had good success with Gorilla brand Wood Glue. This isn't the regular Gorilla glue that foams up and expands, but a different glue altogether.

https://www.gorillaglue.com/glues/woodglue/index.aspx

It doesn't seem to shrink as much as Titebond or Elmers and I had no issues with bubbles in the fillets I made with it.

kj

 

[Micromeister]

most of my models these days have elmers carpenters yellow glue attached launch lugs, fins and fillets. The Titebond molding stuff is fine but just isn't what i'm used to and required cleaning the darn nozzle every time you use it.

If i'm looking for a glass smooth quick and easy fillets that add a little strength to the base glue bond I use 5 minute Devcon epoxy with as small a radius as I can form with a dowel, Q-tip or finger soaked in alcohol. Works very fast and keeps the fins and lugs on for decades.

 

[accooper]

Here is what the LL looks like now, if I can figure out how to attach a picture

 

[JAL3]

Use Titebond Moulding and Trim Glue (TMTG)-- the stuff is great! Goes on smooth and slick, and it's thicker than regular white glue so it WILL NOT RUN around the ends of the launch lugs-- it stays where you put it and doesn't form bubbles or shrink anywhere near as much as regular white or yellow glue as it dries.

I usually use a double-glue joint with yellow glue to put the lug on the body of the rocket (since I usually use double-lugs, a shorter one 'up front' and a second in a fin fillet) and then after they've dried go back and fillet the lugs with TMTG. When it's done it looks every bit as good as epoxy fillets with none of the epoxy hassles or weight. The TMTG makes killer fin fillets as well...

Highly recommend it! OL JR

I tried this out a few months ago based on Luke's comments. I'll never have reason to try anything else again. It works very well.

If you're the Andrew Cooper that came out to Castroville, I'll show you the fillet it did on my Prometheus which will have it's first flight at the November Alamo Rocketeer launch in China Grove.

 

[SteveF]

I think I posted that about trim & molding glue not available at home depot. Looked there recently and didnt see it. Bought it at Lowes. We also have Menards around here and saw it there too. Havent been to Ace so dont know about there

 

[powderburner]

OK, here is what I did. I glued on the launch lug as usual, using wood glue. Put fillets on the lug, twice as usual. Then after that was good and cured, then I used the wood filler over the wood glue.

Your approach works fine, and gets a good glue joint between the LL and the cardboard BT. Don't know if you know this, but both of these surfaces are usually covered with a thin plastic/"glassine" covering that inhibits how just about any adhesive gets a good hold. You should be scuffing this covering (be careful not to sand all the way into the cardboard itself) on both the LL and the BT in the area immediately around the joint, say maybe up to 1/8th inch away. This will give your glue an even better grip, whatever you use.

Your approach to make a primary, structural attachment and then cover with filler/putty/spackle for cosmetics is just fine. Some of the fillers that contain micro-balloons (it makes them light, and easier to sand) can end up in cured form with a fairly soft surface that might show some later damage. You can toughen this outer surface a bit by soaking in a few drops of superglue. Keep in mind that this is not to improve the joint itself, just to toughen the surface of your filler material.

For this kind of thing I like to use the household spackle that is super-light-weight (the kind where you pick up the tub from the store shelf and it's so light you wonder if it's empty). This is the same home-improvement spackle sold for fixing holes in the wall, where you can plaster it into the hole and it won't slump (much) back out. This spackle mix is also full of microballoons and is usually water-based. It is very easy to shape with a wet finger, easy to wipe off excess with a wet paper towel, and easy to wash off your hands. And it absorbs that superglue just fine.

 

[accooper]

Yea, that is me. So I will look forward to your instruction.

Andrew

 

[MarkII]

I think I posted that about trim & molding glue not available at home depot. Looked there recently and didnt see it. Bought it at Lowes. We also have Menards around here and saw it there too. Havent been to Ace so dont know about there

Ace Hardware carries it; that's where I got mine.

MarkII

 

[MarkII]

OK, here is what I did. I glued on the launch lug as usual, using wood glue. Put fillets on the lug, twice as usual. Then after that was good and cured, then I used the wood filler over the wood glue.

Hope this clears up what I did.

Thanks for the input.

Andrew

I have done that, too, on occasion. It works!

MarkII

 

[accooper]

What are micro-ballons?

Andrew

 

[luke strawwalker]

They're tiny little spheres, usually of glass (or other minerals such as talc, etc.) that are used in some wood fillers, spackles, etc. to make them lighter... Imagine them sorta like packing peanuts...

Microballoons, when mixed with epoxy or other adhesives, are sorta like a popcorn ball, in that they take up space that would otherwise have to be filled with the "caramel" (epoxy or adhesive) and yet are lighter, but still have space between them for the adhesive to 'link' to itself and hold it all together... (just like caramel in a popcorn ball, to use a Halloweeny example)...

Later! OL JR

 

[powderburner]

Micro-balloons by themselves look like white dust. If you had a handful it would look kinda like a pile of sugar grains. If you sneezed into it, it would make a cloud of white dust.

These things are used lots by people who work fiberglass as an outer layer to cover over the fibers that show in the last cloth layers. They mix with epoxy to make a filler (with lower density, and easier to sand) just like chopped fiberglass fibers do (when you want reinforcement). They use the stuff by the gallons.

You can buy microballoons at many hobby shops. The R/C guys use them in "hobby" sized amounts, so the containers will be smaller. If you want some, might be more economical to look for them at your local boat or fiberglass shops, but product pkgs will probably be a little bigger.

https://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHZ15&P=FR
https://store.anchormarina.com/anchor/details.php?ITEM=1825007
https://www.eagerplastics.com/7962.htm

 

[MarkII]

More like cornstarch, but let's not quibble.

I bought a pint can of Sig Microballoons from my LHS 3 years ago, and I use it regularly. I still haven't finished denting the top layer inside the can yet, though. Microballoons are actually microscopic sized hollow glass spheres. (They are individually hand-blown by elves, I hear. ) They add quite a bit of volume to the epoxy mix and lower its density and, to a significant extent, its weight. Fin fillets made with epoxy mixed with microballoons are easy to spread smooth and are much less prone to running/dripping before they cure. Once cured, the mixture is easy to sand smooth, partly due to the fact that the microballoons break easily when they are sanded (but are strong and stable when they are intact within the cured epoxy), and partly due to the fact, I suppose, that there is simply less epoxy in the fillet.

Because of this, fillets made from an epoxy/microballoons mixture are not as strong as fillets made from epoxy alone. But that is not necessarily as bad as it sounds, because strengthening the joint is not the only purpose of fillets. Fillets were originally used in aircraft design to improve the airflow over the wings and other protrusions from the fuselage. So they perform a dual function when they are used in rockets. A launch lug has a very large of bonding surface relative to its size and mass, so lugs don't really need fillets to help give them strong bonds to the airframe, but they do need them to help smooth the flow of air around them. Depending upon the brand of epoxy that is used, an epoxy/microballoon mixture can still be quite strong, though.

There are other additives that can be mixed with epoxy that will actually add strength to it, but they don't reduce the weight as well as microballoons do. Microballoons may be more popular with model aviation builders as an epoxy additive because of their ability to cut down on the weight, while other additives are probably more popular with high power rocket builders because of their strengthening effects.

MarkII

 

[MarkII]

Also, common sense suggests that you should take precautions to avoid breathing either the plain (raw) microballoons, or the dust created by sanding an epoxy/microballoons mixture. Wearing a good quality dust mask, eye protection and a hat seems like a sensible thing to do, as does as changing your clothes (or removing coveralls) and washing any exposed skin after sanding the stuff. (Microballoons or microballoon dust has a slightly salty taste.) A quantity of microballons will puff up to quite a degree when it is exposed to water (due to surface tension on the microspheres, I believe), so getting much of it onto any mucous membranes (especially those inside lungs) seems like something that should really be avoided.

The same thing could be said about any type of sanding dust, though.

MarkII