Launch day. Yikes!

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Senior Space Cadet

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Well, it might have been overkill to epoxy the fins and launch lugs, but it wouldn't have been overkill to epoxy the motor mount together and into the rocket.
I had two fail on me. One apparently blew out the engine block on launch and one blew the whole motor mount out on ejection.
I had a third that seems to have stripped out or broke the engine hook.
Of those three, one is fixable, and two probably aren't, though I may try putting a screw in retainer on the rocket that broke the hook.
Otherwise, all the rockets flew great, until they broke.
29er on launch pad.jpg
Big Mama on launch pad.jpg
 

neil_w

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That's unfortunate, but epoxy is not the answer. A properly glued (with white or yellow glue) mount and/or engine block should never break loose in an LPR. *Especially* the engine block, which is generally a .25" rolled paper ring with a ton of surface area on the glue joint.

How exactly did you glue them in? Next time, perhaps, take pictures while building and we'll see if we can identify the problem.
 

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All I can figure is I either didn't use enough glue or, in the case of the whole engine mount shooting out the back, I put the glue too far up the body tube so the motor mount never reached the glue. I was using D motors in both cases. One was a Quest 18mm D16 and the other was a 24mm D12.
The good news is they flew well and I still haven't even mounted the engines in two of the rockets I built this week so I can be sure of getting them glued in right.
I might try a different glue. I was looking at wood glue at Lowe's the other day, and they had some more expensive glues that were supposed to have a stronger bond. I'm using Gorilla wood glue.
I think I need to get stainless hardware for my launch pad. The wing nut, that came with it, is so flimsy, I bent it tightening it up.
Last launch of the day, the launch controller didn't work. To be sure I can launch, nest time, I ordered a better controller.
This hobby is getting kind of expensive.
 

neil_w

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All I can figure is I either didn't use enough glue or, in the case of the whole engine mount shooting out the back, I put the glue too far up the body tube so the motor mount never reached the glue.
That would certainly do it. :)

I might try a different glue. I was looking at wood glue at Lowe's the other day, and they had some more expensive glues that were supposed to have a stronger bond. I'm using Gorilla wood glue.
Gorilla wood glue (or any yellow wood glue) is absolutely, 100% strong enough for this application. I promise you that the strength of the glue is not the issue here.
 

Senior Space Cadet

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That would certainly do it. :)


Gorilla wood glue (or any yellow wood glue) is absolutely, 100% strong enough for this application. I promise you that the strength of the glue is not the issue here.
My big fear is that, after all the work I put into the rocket, the glue grabs as I'm putting the motor mount in and it gets stuck half way. I think that's what's messing me up.
 

neil_w

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My big fear is that, after all the work I put into the rocket, the glue grabs as I'm putting the motor mount in and it gets stuck half way. I think that's what's messing me up.
Ah, well glue grabbiness is a separate issue from glue strength.

For the engine block, this is generally not an issue, particularly if you're using a motor hook. Apply a ring of glue (not too much) just slightly above the final position inside the tube. Push the block in from the top, using a spent motor casing or whatever, firmly and decisively in one shot until the block hits the hook. Then put a fillet around the top of the ring. I always use wood glue for this (TBII) and have never had even a hint of a problem. If your motor mount is cut to length where the block aligns flush with the front end, then put the block on your bench and push the mount down onto it until flush, also super easy.

Installing motor mounts can definitely be trickier. White glue (e.g. Elmer's Glue-All, not the school variety) works for this and is less grabby than wood glue. Epoxy will also work if you prefer. With epoxy you must ensure the mount does not slide out of place while curing, either by holding it in place somehow or ensuring that the assembly is horizontal so gravity will not get a chance to do its work.

In any event, you certainly need to ensure that both the block and the mount are well-glued.

I'm a little curious also about the one you say broke or stripped out the engine hook.
 

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I took a good look at the damage yesterday.
On one of the rockets, the motor mount, as a complete unit, shot out the back. I think glue grab is a factor because I try and put the glue in the body tube, far enough back so that the first centering ring doesn't have to go much past it. I also noticed that the engine block was loose. I was able to pull it out without much trouble and it was burned underneath.
On a second rocket, the engine block failed, but the rest of the mount stayed intact. This rocket had fins with tabs. The front of the rocket crumpled on impact but might be fixable except that I have a baffle in this one, so the old motor is stuck between the engine mount and baffle.
The third rocket, the motor retaining hook tore out. Maybe one hook on a 24mm D motor isn't enough. Or maybe the chute was packed too tight or the nose cone on too tight. This rocket could be fixed with a screw on motor retainer, except that it's a 29mm body, so the retainer cap is larger in diameter than the body tube.
 

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Glues:
If I recall correctly, there was a wood glue at Lowe's that was a slower cure. This would be bad for mounting fins without tabs (I just hold them till they stick) but might have less unwanted grab.
I've used more epoxy than your average 500 people combined. Gallons of it. For rockets, I've been using five minute with the self mixing tube. Very convenient, but it keeps coming out of the end long after you want it to stop, and it's runny. Pretty hard to not make a mess. The good thing about it is it doesn't grab instantly. You can move stuff around. As Neil says, this can also be a problem too. The other problem is one brand only gives you one mixing tube and another brand only gives you two. Unless you want to throw away a lot of epoxy, you have to do all your work, or at least half, at the same time. When I was trying to make epoxy fillets on the fins and launch lugs of three rockets, by the time I got done squirting epoxy on the last rocket, the epoxy on the first rocket was running all over and starting to harden. I have, at least, a gallon of epoxy left over from boat building, but it's old. I have tubs of epoxy in paste form, but it's old too. Sometimes you can bring it back to life by heating it up. I've microwaved resin and hardener. I might place another order with System Three. You should check them out and some of the boat building supply companies. They generally deal in larger quantities than you need for building rockets, but the range of glues and additives is amazing.
 

jrap330

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Glues:
If I recall correctly, there was a wood glue at Lowe's that was a slower cure. This would be bad for mounting fins without tabs (I just hold them till they stick) but might have less unwanted grab.
I've used more epoxy than your average 500 people combined. Gallons of it. For rockets, I've been using five minute with the self mixing tube. Very convenient, but it keeps coming out of the end long after you want it to stop, and it's runny. Pretty hard to not make a mess. The good thing about it is it doesn't grab instantly. You can move stuff around. As Neil says, this can also be a problem too. The other problem is one brand only gives you one mixing tube and another brand only gives you two. Unless you want to throw away a lot of epoxy, you have to do all your work, or at least half, at the same time. When I was trying to make epoxy fillets on the fins and launch lugs of three rockets, by the time I got done squirting epoxy on the last rocket, the epoxy on the first rocket was running all over and starting to harden. I have, at least, a gallon of epoxy left over from boat building, but it's old. I have tubs of epoxy in paste form, but it's old too. Sometimes you can bring it back to life by heating it up. I've microwaved resin and hardener. I might place another order with System Three. You should check them out and some of the boat building supply companies. They generally deal in larger quantities than you need for building rockets, but the range of glues and additives is amazing.
System 3 is a known entity in rockets. Nothing new there. Look at how you build and glue the mount. Use an old Estes instructions, they state use scrap balsa to put glue for forward ring into air frame....a lot of times I add glue to that front ring and slide the mount in,, not good sometimes I quickly pulled it out.... once in...put glue around the aft ring and leave it alone for drying/curing As Neil and others stated white glue or wood glue is all that is required. There is no need for epoxy on model rockets. I have use Elmer's white glue (kid) and for last xyz years : Elmers wood, Tight bond II wood glue and now Gorilla wood glue. I prefer wood to white since it is thicker (less runny) and therefore stronger. Motor hook loose..if there is no green centering slide over the hook..wrap masking tape around hook to help hold it on.
 

neil_w

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There is no need for epoxy on model rockets.
I confess I have grown fond of using epoxy to install motor mounts, just because it eliminates the hurry and worry. I can take my time, slide into position, adjust as necessary, and be good. Also no shrinkage so no Coke bottle effect.

I also generally use epoxy for bonding plastic or 3D-printed parts to wood or paper.

That's about it though.
 

jrap330

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I confess I have grown fond of using epoxy to install motor mounts, just because it eliminates the hurry and worry. I can take my time, slide into position, adjust as necessary, and be good. Also no shrinkage so no Coke bottle effect.

I also generally use epoxy for bonding plastic or 3D-printed parts to wood or paper.

That's about it though.
yes for plastic,I just epoxy my plastic fins, into python that crash.
 

Senior Space Cadet

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System 3 is a known entity in rockets. Nothing new there. Look at how you build and glue the mount. Use an old Estes instructions, they state use scrap balsa to put glue for forward ring into air frame....a lot of times I add glue to that front ring and slide the mount in,, not good sometimes I quickly pulled it out.... once in...put glue around the aft ring and leave it alone for drying/curing As Neil and others stated white glue or wood glue is all that is required. There is no need for epoxy on model rockets. I have use Elmer's white glue (kid) and for last xyz years : Elmers wood, Tight bond II wood glue and now Gorilla wood glue. I prefer wood to white since it is thicker (less runny) and therefore stronger. Motor hook loose..if there is no green centering slide over the hook..wrap masking tape around hook to help hold it on.
I know all of this. I'm pretty much doing all of this. I think there are two causes for my problems. Not using enough glue, and not measuring the correct distance inside the body tube. If the motor mount never reaches the glue, the glue isn't going to do much.
The engine hook was under at least one and maybe two centering rings (can't remember). It ripped a line down the motor mount tube.
I see three problems with gluing low power rockets with wood glue.
1-Wood grab
2-Glue causes parts that already fit tight to swell.
3-Some parts are too tight and some are too loose.
I was under the impression that most of you don't use epoxy, at least for low to mid power. So I would think that System Three is not that well known among you. I would guess the percentage of you that have actually gone to their web site is very, very small. Just trying to help.
 
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Senior Space Cadet

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I'm going to try two new glues. I went to Lowe's and bought bottles of Titebond III Ultimate wood glue and Titebond Quick and Thick.
The Ultimate wood glue says "superior strength, longer assembly time". I'm hoping this means less glue grab.
Quick and Thick is a multi-surface glue, not just for wood. Says it's 2x faster, 3x thicker. Might be good for some things. I'll have to experiment.
 

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Titebond or regular wood glue is 100% fine, people have been using them for LPR rockets since like, 1960. Your glue is not the problem, the correct application is the problem.

The general rule on wood/white glue is that "less is more", and I have always found I used too much instead of too little. Over glue can give you just as many issues, as I found when my 13mm bird died to an engine seized inside when the glue remelted.

Engine blocks: Push the engine block up from the rear with a spent motor casing. Apply glue where you expect the block to be. Use a q-tip or small dowel. Push engine block into place and remove spent motor casing.

Engine motor mounts: Apply glue where you expect mount(s) to be, then push into place. If you have more than one centering ring and you're pushing an MMT into place with both centering rings at once, use a little extra glue on the first one, but not much.

Applies to everything: Sand parts until you can *smoothly* take them in and out *before* glue application. If they give you *any resistance at all* while you are trying to fit them together, go back and sand again. This has been 90% of my "got stuck" problems. Sand sand sand.
 

jqavins

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For placing glue for the forward centering ring, what I do is:
  1. Place the assembled motor mount next to the body tube at the intended height;
  2. Hold my application stick with its inside end positioned;
  3. Place a mark on the stick at the bottom of the body tube;
  4. Use the mark to know how far to stick the stick up the tube to apply that forward glue stripe.
Also, I like to place somewhat more glue up there than is strictly needed. As the motor mount is pushed in it should "snow plow" glue ahead of it. Then I turn the rocket nose up, and the glue should slump down, giving me a naturally formed fillet. I say "should" do this and that because I've never x-rayed one after assembly. But I've also never had a motor mount push out in flight, so if it isn't working then at least it isn't doing any harm.

You mentioned holding fins in position until they stick. Nowadays I use a plastic jig from Estes for most LP fins.
1596554204243.png
When I didn't have this, I found that I couldn't reliably hold a fin long enough to stick with wood glue, so I took to doing this:
  1. Mark the fin locations, of course;
  2. Place a drop of thick CA about a half inch in from each corner of the rood edge;
  3. Place one corner of the root edge at its end of the marked line; because the glue is a little way in from the corner it hasn't made contact yet;
  4. Lower the fin until it makes contact along the whole root edge and the drops of glue cure in just a few seconds.
  5. Run a little thin CA along the root edge; thin CA will easily penetrate the fin-to-tube joint;
  6. Add fillets with wood glue.
The fillets should be enough without the thin CA. It's belt and suspenders.

Some say the Thick-'n'-Quick is good for fillets; I haven't tried it (yet). They also say it isn't good for much else (but I'm not saying it isn't good for anything else).
 

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jrap330

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I'm going to try two new glues. I went to Lowe's and bought bottles of Titebond III Ultimate wood glue and Titebond Quick and Thick.
The Ultimate wood glue says "superior strength, longer assembly time". I'm hoping this means less glue grab.
Quick and Thick is a multi-surface glue, not just for wood. Says it's 2x faster, 3x thicker. Might be good for some things. I'll have to experiment.
try quick and thick on plastic cardboard junctions and report back.Estes recommends
plastic model glue which after awhile looses adhesion.
 

jqavins

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try quick and thick on plastic cardboard junctions and report back. Estes recommends plastic model glue which after awhile looses adhesion.
Do you mean adhesion to the cardboard? It shouldn't ever lose adhesion to polystyrene, since that's a chemical weld.

In the old days, Testors green label was recommended for balsa, and as I recall worked fine for paper, where the red label was for plastic (polystyrene). They were almost the same, the same solvent and different amounts of polystyrene filler. Nowadays there is a different solvent in the red label, and I don't know if they even sell the green label anymore. If they do, and if it's still as good for paper as for balsa, I wonder if a thin smear of green on the cardboard before application of the red would work any better than red alone.
 

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It sure is: https://www.rocketryforum.com/threads/doing-fillets-with-titebond-quick-and-thick.148632/

Nowadays I do prefer to apply a *thin* fillet of regular wood glue first, to really soak into the joint. Then Q&T on top.
ok read all the 2018 post on fillets, how is quick and thick on gluing find and motor mounts
Do you mean adhesion to the cardboard? It shouldn't ever lose adhesion to polystyrene, since that's a chemical weld.

In the old days, Testors green label was recommended for balsa, and as I recall worked fine for paper, where the red label was for plastic (polystyrene). They were almost the same, the same solvent and different amounts of polystyrene filler. Nowadays there is a different solvent in the red label, and I don't know if they even sell the green label anymore. If they do, and if it's still as good for paper as for balsa, I wonder if a thin smear of green on the cardboard before application of the red would work any better than red alone.
Yes adhesion to cardboard...green label not sure I ever saw it for sale
 

neil_w

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ok read all the 2018 post on fillets, how is quick and thick on gluing find and motor mounts
It's very sticky and messy to work with. I would never use it for motor mounts and I'm not too enthusiastic about it for fins either, since it seems to me too thick to soak into the wood or paper on either side of the joint.

I stick with (pardon the expression) more liquidy glues (TBII, white glue, or epoxy) for structural bonding, and use the Quick and Thick exclusively for fillets, for which it excels.
 

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It's very sticky and messy to work with. I would never use it for motor mounts and I'm not too enthusiastic about it for fins either, since it seems to me too thick to soak into the wood or paper on either side of the joint.

I stick with (pardon the expression) more liquidy glues (TBII, white glue, or epoxy) for structural bonding, and use the Quick and Thick exclusively for fillets, for which it excels.
Ok, neil....next in Home Depot..I will look out for it.
 

neil_w

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Ok, neil....next in Home Depot..I will look out for it.
I don't believe HD sells it in single-bottle quantities. True Value and Ace Hardware (where I bought mine) both carry it.
 

jrap330

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I don't believe HD sells it in single-bottle quantities. True Value and Ace Hardware (where I bought mine) both carry it.
thanks..noted.
 

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If you don't use enough glue in the BT, the motor mount can get partially stuck in the tube. I usually use two gobs of TBII on the end of a chopstick. I push the mount in and then glue the inside before inserting all the way. This gives you about 15 seconds to position it properly. As an added step, I like to epoxy the exposed face of the mount.

I like this series of videos. He promises he'll upload more painting videos that I'm looking forward to.

 
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