First MPR build (Ventris) Couple questions

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jerrymazzer

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Like many of the posters I've seen on here, I'm returning to model rocketry after about a 25 year hiatus since launching LPR as a kid. I just started building a Ventris. I dry-fit everything and it seemed good to go so I jumped in. I got the motor mount assembled and installed (all tite-bond) and am reasonably confident that it's secure. I then proceeded to attach the two body tubes using the 4" coupling tube, and this is where I hit my first snag. I guess I took too long applying glue to the coupling tube. When I went to slide it into the lower body tube, It stopped about 3/4" short of the center mark. I couldn't get it to budge. So, panicking, I tried to quickly glue and slide on the upper body tube. It, too, stopped about 3/4" short of the center mark on the coupler. So now, my lower and upper body tubes are separated by about 1-1/2" of exposed coupler tube, with 1-1/4" of coupler glued inside each body tube. The alignment of the two tubes is slightly off, too. If I roll the entire body along a tabletop, the body shows about a 1mm dogleg. Is this enough to warrant cutting the lower body tube, getting a new coupler tube and upper body tube, and regluing? Or is a 1mm dogleg not enough to disastrously affect flight? I'll be launching this on a G40-7W the first go. I've got a G80 waiting in the wings if all goes well. Second question is in regards to the plastic transition piece. I've seen some posts on here regarding how some of them were too loose, and an offer from Estes to replace them. How loose is too loose? With everything dry-fit, I can move the nose cone back and forth about an inch from the line of the body. Seems like it ought to be more snug, but is it worth requesting the replacement, or should I just use masking tape to snug it up? Also, I'd rather not glue the nose and transition to the av bay(?-the bigger bit at the top of the rocket). I'd like to get an altimeter and sonic locater to put in that section, so I'm planning to attach the two plastic bits together with some elastic banding or shock-cord.

Well, this is a bit longer post than I'd planned, but thanks for reading and thanks for any advice!

-jerrymazzer
 
I'd redo it if it were mine, but not out of any sense that it's a flight disaster waiting to happen. An aesthetic disaster, possibly...

Depending on the amount you use, the temperature, the snugness of the coupler, the phase of the moon, and possibly quantum effects, yellow wood glue can indeed grab a coupler or motor mount almost instantaneously once it stops moving. Ditto Elmer's Glue-All in the new formulation that's been on the market a couple years. I still use Elmer's yellow for most of my wood/cardboard glue-ups but have switched to epoxy for couplers and motor mounts.
 
I'm not sure what to advise about what to do with the rocket now. But I was going to say basically what Rich said above --- wood glue can really grab before you are done positioning. Even if you dry fit first, and make sure everything will slide together dry, there can still sometimes be problems. I think the glue soaks into the cardboard and makes the cardboard expand, making the fit tighter. I also think that as moisture soaks into the cardboard, the glue gets immediately tackier. That combination means that the joint can seize tight as soon as you stop moving. I've had more success gluing couplers with white glue, like Elmers Glue All, but it sounds like Rich is saying that has been reformulated and maybe doesn't work the same way it used to...

I am not a fan of working with epoxy. What other brands or types of wood glue or white glue have people found to have good properties for gluing couplers without grabbing? Or is there a technique that avoids this problem?
 
... I am not a fan of working with epoxy. What other brands or types of wood glue or white glue have people found to have good properties for gluing couplers without grabbing? Or is there a technique that avoids this problem?

Gorilla polyurethane

Original-Glue.png


to the OP, I think that a 1mm dogleg will not have a disasterous (or even a mildly unpleasant) affect on the flight.
 
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I am not a fan of working with epoxy. What other brands or types of wood glue or white glue have people found to have good properties for gluing couplers without grabbing? Or is there a technique that avoids this problem?
In a test of coupler gluing I did last summer, a thin application of Elmer's Glue-All seized up immediately. A thicker application — 2 or 3 times as much — gave me a minute or two of working time. (With Elmer's Wood Glue, both a thin and a thick application grabbed immediately.)

That was one trial of each; a proper test would involve 20 or so trials of each, and better controls on other factors like temperature, timing, and so on. All I can say is, Glue-All can grab and it can stay mobile.

Thick applications of Glue-All might work for you. I don't trust the stuff.
 
I can confirm Rich's test results from my experience: a thicker application of white glue gives you a little more working time with couplers. BUT... you still have to move fast and it still may grab sooner than you want. I prefer the alternatives now.
 
Don't feel bad, I was installing a Sunward Baffle in my 2.6" TLP Alarm Kit that I totally bashed, and the Baffle did'nt go as deep as I wanted it. As I applied more Pressure, I caused the Body Tube to crumple where I had made Slots for the Fins. I felt like an Idiot for making such a Mistake, but It was a learning Experience and I was able to make it look right. Titebond II sets up fast, and when your doing internal Body Tube stuff, your better off with Titebond III, or Watering down the TB II. I hope your Build turns out okay, and welcome back to the Hobby.
 
Samb and Rich, thanks for the info.

Regarding the Gorilla Polyurethane, I have only used Gorilla glue once, and it was not for a rocket application. As I recall, instructions were to moisten one side of the joint with water and the other side with the glue. And then after the sides were joined, the glue tended to expand. Is that the same stuff you are talking about and the same procedure? Is there any issue with the expansion?
 
Jerrymazzer,

If the dogleg is not so bad that the rocket will not fly properly, and the main problem now is cosmetic, you can fix it without cutting out the coupler and starting over. Measure the length of exposed coupler. Then cut that length out of a piece of 2-inch body tube. You can either cut it from the top end of your body tube or from a new piece if you have one. Then make a cut in that piece lengthwise. Now you have a sleeve that you can open and glue over the exposed piece of coupler. Use wood filler to fill any gaps. Sand, prime and paint --- no one will ever know except for those of us who have read the thread, and we won't tell.
 
Samb and Rich, thanks for the info.

Regarding the Gorilla Polyurethane, I have only used Gorilla glue once, and it was not for a rocket application. As I recall, instructions were to moisten one side of the joint with water and the other side with the glue. And then after the sides were joined, the glue tended to expand. Is that the same stuff you are talking about and the same procedure? Is there any issue with the expansion?

I've been using it for couplers and motor mounts for 4 or 5 years and have had no ill effects. For this application I don't add any extra moisture, ambient humidity may cause a little foaming. One bead around the inside of the tube, one around the coupler, smooth with a gloved finger or coffee stirrer/popcicle stick/tongue depressor, then insert the coupler with a couple of twists to get full glue distribution.
 
Samb, do you succeed in using more than a small fraction of a bottle before it hardens?

The most recent bottle I've bought, I tried squeezing out most of the air before capping it, and I'm storing it upside down. We'll see if that helps. Also, I did notice they'd redesigned the cap, so that may improve its shelf life too.
 
Samb, do you succeed in using more than a small fraction of a bottle before it hardens?

The most recent bottle I've bought, I tried squeezing out most of the air before capping it, and I'm storing it upside down. We'll see if that helps. Also, I did notice they'd redesigned the cap, so that may improve its shelf life too.

Yeah, that is a problem Rich. I've had that happen (bottle of "amber") once, even when buying the small bottle. I found a pack of "one-hitters" last week at a local Walmart. Can't remember the exact price right nowSingle_Use_Tube-1.png.

https://www.gorillatough.com/index.php?page=single-use
 
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Wow! Thanks for all the replies, everybody. Still trying to decide how to proceed with the fudged coupler. I'm leaning towards hacking off the lower tube and either sanding and trying to reglue what is now exposed coupler into the lower tube, or just getting a new coupler and upper tube. I kinda want to avoid an aesthetic disaster... Now to get these fins on straight!
 
Just because one guy says he doesn't like epoxy is not a good reason to totaly dismiss the product.

A 30 minute epoxy ( www.hobbylinc.com/epoxy ) would work well for joining two tubes with a coupler. Epoxy in its liquid state acts more like a lubricant then an adhesive.

The clock starts ticking when the contents of the two bottles are mixed together. Since only a small amount of the epoxy will be needed to join the tubes, only a minute will be used up mixing up a batch. This will easily leave you more then a quarter hour to adjust the tubes before the epoxy sets. You will still have time to clean off the epoxy that oozes out of the seam between the tubes.

Q-Tips with Rubbing Alcohol on them will get any epoxy buggers off the surounding areas.

How you proced with the repair or replacement of the tubes is pretty much up to you.

I would suggest laying down news paper or plastic wrap on whatever surface you use to roll and aline the tubes. Epoxy can make its way to the dammedist places if forethought and precautions are not taken.

wearacup.jpg
 
Yes, by all means, do NOT dismiss epoxy. But if you do desire an alternative I have found polyurethane glue to be a satisfactory substitute. :2:
 
Yeah, just because I personally don't like using epoxy doesn't mean it's a bad adhesive or there's anything wrong with it, as long as you use the right precautions. It sounds like the working properties are just right for couplers.

I personally do not like epoxy, because the smell has always bothered me. And as I've gotten older, I've learned it's not just unpleasant, but toxic. There've been a few members of the forum who have posted about their epoxy allergies, and it does not sound fun. I can't see myself using gloves and a gas mask to glue in a coupler. I like the fact I can get wood glue on my fingers and just peel it off later. (I actually kind of enjoy that!) Honestly, I'm not a big fan of CA either. The fumes not only burn my nose hairs but also irritate my eyes. I don't even really like plastic cement because of the fumes.

That said, I will use CA or plastic cement when called for. And I'll be using JB Weld epoxy when gluing in the retainer on my Leviathan (whenever I get back to that). When it's necessary, it's necessary. But if given a choice I prefer my rocket materials "organic."
 
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