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Smooth launch lug joints?

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Landshark

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On the last few kits I've built, I've been noticing that the joint between the launch lug (LPR kits) and the body tube seems to get a lot of rough spots / porosity in the glue fillet (white or yellow glue used). It looks "ragged" and bugs me.

It's almost like the two round surfaces or the glue being used is causing air bubbles or something. I try to re-fillet with white glue (supposed to shrink less, right), but it doesn't seem to help much. I'm not having any problem with fin fillets by comparison.

Anyone have any tips on getting that particular fillet to be smooth? I might try FnF (for finish, not for strength) but that might be a little hard to sand down.
 

DAllen

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Bubbles and pin holes seem to be a fact of life when it comes to using wood glue in fillets. When that happens on my LPR rockets I use Drydex. It is a drywall spackling compound that goes on purple and dries white. Very very sandable and doesn't seem to add a lot of weight. You can typically find Drydex at most hardware stores in the aisle with the drywall tape, adhesives, etc.

-Dave
 

Zeus-cat

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I know this is not directly answering your question, but it does make for a nice looking launch lug mount and it is very strong.

I started placing small wooden strips on each side of any launch lugs that might come under a lot of stress. I sand them down a little so they form a cradle for the lug and also conform to the body tube. I then glue them onto the rocket and then add the launch lug. I seal the strips of wood with white glue and sand them once everything is dry. You could use basswood or other lightweight strips that you should be able to find at most hobby shops.

lug reinforcing strips.jpg
 

judo

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I go the wood filler route. It actually sands easily. I drip thin CA onto it once I have the desired shape.
 

hcmbanjo

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Because of the steep angle, it's easy for air to get trapped in lug/body tube joint.

On the lug fillets, lay the glue slow so air doesn't get trapped. After the glue is layed down, you can run a toothpick down the joint to clear any air out. If bubbles show up, use the tip of the toothpick to pop the bubbles. The toothpick will pop the bubbles easier than the tip of a hobby knife. If the glue is still wet, the gap from the popped bubble might close up.

If there is still problems, just keep adding glue and smoothing it out, letting it dry between applications. Probably four fillets should close it all up.

After fillets, I've used Elmer's Carpenter's Wood Filler (Fill N' Finish) to smooth out lug and fin joints before. Lay some fine grit sandpaper around a dowel and sand it smooth.
 

Trident

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Besides wood strips and fillers mentioned previously, I have used epoxy, applied sparingly, to make a smooth fillet. With a gloved finger, dip in rubbing alcohol or lacquer thinner and wipe the joints. This makes the epoxy fillet smooth, usually requiring little sanding.

I have also used Titebond Trim and Molding Glue, which is great because it does not form bubbles.

Why two methods? I use the epoxy on larger models where I want a larger joint. The Titebond is really good for smaller models where I'm looking to add a very small fillet.

It all boils down to personal preference, but I'm liking the Titebond solution more and more.
 

luke strawwalker

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On the last few kits I've built, I've been noticing that the joint between the launch lug (LPR kits) and the body tube seems to get a lot of rough spots / porosity in the glue fillet (white or yellow glue used). It looks "ragged" and bugs me.

It's almost like the two round surfaces or the glue being used is causing air bubbles or something. I try to re-fillet with white glue (supposed to shrink less, right), but it doesn't seem to help much. I'm not having any problem with fin fillets by comparison.

Anyone have any tips on getting that particular fillet to be smooth? I might try FnF (for finish, not for strength) but that might be a little hard to sand down.
Yessir, I have the solution for you.

Go to your local big box hardware store (Lowe's, Home Depot, etc.) and get you a bottle of Titebond Moulding and Trim Glue. It should be right on the shelf beside the Titebond II and Titebond III yellow wood glues, Elmer's Wood Glue, etc. This stuff is the absolute BEST stuff for making fillets that I know of.

http://www.lowes.com/lowes/lkn?acti...9-_-Titebond 8 Oz. Molding and Trim Wood Glue


It goes on pretty thick, about like caulk or toothpaste, so it stays put-- it doesn't run down to whichever end of the fillet is lower. It doesn't shrink hardly any, and it doesn't develop bubbles that then turn into little hollow spots while drying. It is easy to smooth out and work with water, and cleans up with water, like regular yellow glue.

Once you try this stuff, you'll be sold and won't bother using anything else... :)

Good luck! OL JR :)
 

Stymye

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use thin layers, 2 or mabey 3 .. that will stop the pin holes/shrinkage.iIuse titebond III..it took a bit of getting used to

if it's still not smooth enough , run a thin layer of easily sandable filler over them
sand..no special technique or glue is needed.

you can get those smooth, melt into the body tube fin joints ..just takes a little patience and practice..

the key is finding what works for you ...sticking with it, and perfecting it.

alot of the great builders on this forum use hardly more than white glue... and know how to use it ..lol
 
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jj94

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I recommend what Styme said. That's generally what I tell people when they wonder about the gaps and such in wood glue fillets. Keep the layers thin enough that bubbles won't be able to form that easily, and if they do, you should be able to spot them out immediately due to the thinness of the fillet. Just repeat the process over and over to build the fillet up to the desired thickness.
 

Micromeister

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To date the vast majority of my models regardless of size have LL fillets geneally of epoxy. It's just the way things turn out. Of coarse if the fin fillets are some other product, that the Launch lug fillets would be the same.

That said I've just purchased a bottle of the Titebond Molding and Trim glue. and it's some really interesting stuff! I've only experimented with it on one model so far but WOW! as Pippen reported in another thread the stuff goes on almost like a thin puddy, smooths out with a moist finger, stays were you put it and dries smooth and air hole free. The Model I expermented on was a Fliskit "Big Honk'in Rocket" which has a tiny LL that I moved to a fin/body joint location. The glue worked like a charm in the mulit level stepped area around this application.
Very Nice stuff, if it works on a larger models Fin fillets and LL fillets as well as it did on this test piece I'll be a big fan.

PS: Only draw back I see is you have to keep the nozzle clear or it clogs up pretty badly. but a quick cleanout before it hardens up if left overnight only takes a second or two.
 

Zack Lau

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I used thick superglue--a good chance to use the 40% off coupon at Michaels. It is much lighter than epoxy. I orient the model horizontally and add a drop or two of superglue--sometimes I'll use a piece of wire to move the liquid around. It takes a while--I do two fillets at a time and do something else while waiting for the glue to dry.
 
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Sleepy_Steve

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I just throw a little bit of paper (using wood glue) over the lugs if they show fatigue damage or if I anticipate a lot of stress being put on em.

Works wonders for strength, but I suppose the finish suffers a tad. Doesn't bother me though, all I care about are strength and flight characteristics.
 

jj94

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I used thick superglue--a good chance to use the 40% off coupon at Michaels. It is much lighter than epoxy. I orient the model horizontally and add a drop or two of superglue--sometimes I'll use a piece of wire to move the liquid around. It takes a while--I do two fillets at a time and do something else while waiting for the glue to dry.
Yeah, but CA gets pretty brittle as it ages. I personally think it's a bad idea to use CA for strength.
 

MarkII

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Yeah, but CA gets pretty brittle as it ages. I personally think it's a bad idea to use CA for strength.
I think I know what Zack Lau is talking about. I have used BSI Maxi-Cure CA for LL fillets on occasion. I lay down a bead of it along the joint and then quickly swipe it with a gloved finger. Then I do the other side. With both fillets layed in, I hit the area with BSI Insta-Set (CA accelerator). This instantly turns the Maxi-Cure glass clear and hard as a rock! The bond is not like a typical CA bond - it is much more like epoxy (really, really strong epoxy) or Lucite (which is, in a way, not far off from what the catalyzed Maxi-Cure is). The stuff clings fiercely, too. I have, on a couple of occasions, had to remove and replace components that were bonded with this method. The stuff is tough! I had a devil of a time breaking/cutting the component loose each time and then removing the hardened Maxi-Cure. (Removing cured epoxy is actually easier.) I have a hard time imagining how this catalyzed Maxi-Cure could ever become brittle and crack off.

The only problem with the technique is timing it right to get a smooth fillet. If your timing is way off when you hit it with the Insta-Set, the Maxi-Cure will bubble instead of staying smooth, and it be cloudy in appearance. If your timing is only just off, the fillet will be crystal clear but will have a slightly uneven surface. It will still be absolutely rock hard, though, and you can smooth it out with a round needle file.

I don't use this technique all the time because using Insta-Set with CA involves a bit of a juggling act, in three rings no less. In order to help keep my bottles of CA from hardening, I keep my bottles of Insta-Set in a sealed container (a coffee can) in a separate room in my house. When I want to use it, I take the Insta-Set outside, then return to my workshop and apply the CA, and then take the model outside and apply the Insta-Set there. I leave the model outside for awhile, and on my way back into the house, I stop at the kitchen sink and wash my hands. So as you can see, there is a lot of rigmarole involved. But the lug fillets that I create with it are very solid.

MarkII
 

Multi-Stage

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I glue them in place with epoxy and then use amixture of microballons and epoxy then a small wooden dowel to smooth it out. Then make sure it doesn't run. Best lookin LL I've seen.
 

Micromeister

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Have to agree with JJ;
Even the very best CA's become brittle in as little as a year. Some "Seem" incredably strong initially but over time they do by their very Chemistry become extreamly brittle. USA Gold (a Pratt Hobbies Product) is one of the very best CA formulas on the market but with age it to becomes increasingly less flexable and brittle. Mark; I hate to be the one to tell you, nor do I want to sound like a wiseguy or know-it-all, but Accelerators by their nature hasten the onset of CA brittleness.
Since I started keeping my CA bottles in zip-lock bags when not in use. Capped except when in actual use and the CA bottles on opposite sides of the table, ABOVE the height of any accelerator bottles ( Accelerator vapors are heavier then air) I haven't lost a single bottle of Thin or Medium CA.
My CA brand of choice is Zap, but that's a choice based more on price then "Best";)
Over a long time i've seen far to many CA constructed models fly apart in midair as they age. I'd never use CA to attach or Fillet LL or fins on any model I plan on keeping longer then a year.

Besides the small to tiny amount of Epoxy (with or without microballoons) used in fillets and smoothing out LL attachments just isn't worth talking about on anything other then BTC competition models.
There are also Other types of glues that lend themselves to fillet applications like good old Ambroid cement, something the RC airplane guys have sworn by for generations. It's a great fillet and fin attachment glue for that matter as it retains some flexability for life. I have a few models with fins and other attachments with this stuff that are in that 30+ year range still at tight as the day after they were installed;)

For general sport flying you want whatever adhesives or glues used to outlast the flying life of the model.. some of which can be 30 years or longer. Keep CA use to spot tacking and other non-structural uses on sport flying models or those short lived 3 to 6 flight Competition models.

This new Titebond Molding and Trim Glue is far to new to have a track record, but it sure looks very promising. I know i'm planning on giving it a very good round of tests with planned upcoming builds.
 

Zack Lau

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Actually, the Superglue is just used for appearance--it is an easy way to get that perfectly smooth surface Landshark wanted. Typically I'll use yellow glue to attach the launch lugs, as it allows for more precise adjustment.
 

hcmbanjo

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I've tried the Titebond Molding and Trim Glue.
Be careful, it "skins" over very quickly.
Typically I'll finger smooth a white glue fillet 2 or 3 times. By the time I got to the 2nd smoothing of the Titebond product I found myself pulling and moving the (already) drying outside edge.
So with Titebond, fillet one joint at a time, Smooth once and let it dry.

Micromeister is right, the nozzles will clog. If you don't keep it continually cleaned, small dried pieces will end up in your fillet. Those dried pieces will be bumps in your finished fillets.
 

MarkII

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Have to agree with JJ;
Even the very best CA's become brittle in as little as a year. Some "Seem" incredably strong initially but over time they do by their very Chemistry become extreamly brittle. USA Gold (a Pratt Hobbies Product) is one of the very best CA formulas on the market but with age it to becomes increasingly less flexable and brittle. Mark; I hate to be the one to tell you, nor do I want to sound like a wiseguy or know-it-all, but Accelerators by their nature hasten the onset of CA brittleness. ...
Well, we shall see. Time will tell. Although I haven't been at it on a continuing basis for as long as you have, I'm not exactly new at this rocketry thing. I've been around the block a few times already. As you pointed out, not all CA formulations are identical, even within the same brand's product line. You may also recall me mentioning that I didn't use that technique all that often. Far more often, I use either 30 minute epoxy, yellow glue or white glue. I am a big fan of Aleen's Quick-Dry Tacky Glue. This is the kind that is in the silver-colored bottle, not the more familiar brown-bottle variety. It is my favorite white glue. For yellow glue, I mostly use either Titebond II or Titebond III, but I also have a bottle of Gorilla Wood Glue that I am trying out.

I can't say anything about Ambroid Cement. I have certainly heard of it, but I have never seen any of it in any hobby shops that I have visited.

MarkII
 
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RimfireJim

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Aleene's Tacky Glue. Appears to just be a thick PVA (Like Elmers Glue-All, but thicker). Probably works well for the same reason the moulding and trim glue does, which I haven't tried. Works a lot better for fillets than Titebond I/II/III.
 

Zack Lau

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Ambroid is typically sold in hobby shops that also sell rubber powered free flight airplanes--it is very light and sands easily, even when glued to balsa. Our LHS also sells Sig-ment, which is quite similar. Both release toxic fumes. :dark:
 

Micromeister

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Ambroid is typically sold in hobby shops that also sell rubber powered free flight airplanes--it is very light and sands easily, even when glued to balsa. Our LHS also sells Sig-ment, which is quite similar. Both release toxic fumes. :dark:
Zack:
It's not just used by the free flight folks it's used alot to this day in RC Aircraft (Stick & Tissue) model construction as well.
Use this material with the Double glue joint method and forget about that joint for the rest of the models life.
It does have some pretty tough fumes but then again I wish I had a Penny for everything we used in this..well most hobbies that has something "toxic" in it.
I've been using the stuff for more the 30 year now. Along with tons of other "lethal" materals and I,along with all my kids, family and visiting friends are still around and kicking strong LOL!!! Haven't tried Sig-ment I'll have to give it a try.
 

FatBoy

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I use either Tacky Glue or Wood Glue to attach it, then use some watered down Fill-n-Finish or Wood Filler to smooth it all out. Sometimes (like on this Big Daddy), I will cut an angle on the front (and sometimes the back too) to give it a smoother look.

BD0011.JPG
 

JAL3

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Yessir, I have the solution for you.

Go to your local big box hardware store (Lowe's, Home Depot, etc.) and get you a bottle of Titebond Moulding and Trim Glue. It should be right on the shelf beside the Titebond II and Titebond III yellow wood glues, Elmer's Wood Glue, etc. This stuff is the absolute BEST stuff for making fillets that I know of.

http://www.lowes.com/lowes/lkn?acti...9-_-Titebond 8 Oz. Molding and Trim Wood Glue


It goes on pretty thick, about like caulk or toothpaste, so it stays put-- it doesn't run down to whichever end of the fillet is lower. It doesn't shrink hardly any, and it doesn't develop bubbles that then turn into little hollow spots while drying. It is easy to smooth out and work with water, and cleans up with water, like regular yellow glue.

Once you try this stuff, you'll be sold and won't bother using anything else... :)

Good luck! OL JR :)
I hope you're right.

Based on this post, I went out and bought a bottle of this stuff today.

To me, it sounds like one of those "Too good to be true" things but its going to bother me until I find out for myself.

Were I of a differing faith background, I would assert at this point that you have a lot of karma riding on this one.
 

jadebox

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II started placing small wooden strips on each side of any launch lugs that might come under a lot of stress. I sand them down a little so they form a cradle for the lug and also conform to the body tube. I then glue them onto the rocket and then add the launch lug. I seal the strips of wood with white glue and sand them once everything is dry. You could use basswood or other lightweight strips that you should be able to find at most hobby shops.
As an aside, I recently used a similar method on a larger rocket to ensure that the lugs were on straight. I cut two strips of wood to the length of the launch lug. I glued them together into an H (or I-beam) shape using another strip of wood between them. This was glued to the body tube and it naturally aligned itself so that it was straight. Then I glued the launch lug to the wood assembly.

-- Roger
 

JAL3

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I hope you're right.

Based on this post, I went out and bought a bottle of this stuff today.

To me, it sounds like one of those "Too good to be true" things but its going to bother me until I find out for myself.

Were I of a differing faith background, I would assert at this point that you have a lot of karma riding on this one.
I gave it a try today.

I sure like what I've experience so far. I'm interested in what its going to look like tomorrow.
 

MarkII

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I hope you're right.

Based on this post, I went out and bought a bottle of this stuff today.
So did I. Haven't tried it yet, though. I've got to put the fins on, first!

MarkII
 

JAL3

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Yessir, I have the solution for you.

Go to your local big box hardware store (Lowe's, Home Depot, etc.) and get you a bottle of Titebond Moulding and Trim Glue. It should be right on the shelf beside the Titebond II and Titebond III yellow wood glues, Elmer's Wood Glue, etc. This stuff is the absolute BEST stuff for making fillets that I know of.

http://www.lowes.com/lowes/lkn?acti...9-_-Titebond 8 Oz. Molding and Trim Wood Glue


It goes on pretty thick, about like caulk or toothpaste, so it stays put-- it doesn't run down to whichever end of the fillet is lower. It doesn't shrink hardly any, and it doesn't develop bubbles that then turn into little hollow spots while drying. It is easy to smooth out and work with water, and cleans up with water, like regular yellow glue.

Once you try this stuff, you'll be sold and won't bother using anything else... :)

Good luck! OL JR :)
I examined the results of 2 projects I tried it out on. I'm convinced.

Thanks Luke:D
 

o1d_dude

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I've been using the Titebond Molding/Tack glue since Luke first mentioned it a month or two ago.

I squirt it on from the nozzle and then quickly smooth it out with a small popsicle stick for great results. Finishing touches are applied with a dowel wrapped in sandpaper as needed.
 
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