I'm building a Photon Disruptor (#3025). I'm one of these people who refer to the instructions while building ("refer to", I said, not "follow") and I noticed something I hadn't seen in any other kit instructions before. They have you build the motor mount first, then the fins, glue the fins on and the body tube sections together, and only then when the model is otherwise nearly completely assembled, put the motor mount in.

I got to wondering why, and then started wondering why not. I can think of a couple of advantages, neither one particularly compelling: If you're building in a hurry, this gives the motor mount glue time to dry before you start trying to shove it into place; and if something goes horribly south in mid build and you end up having to trash it, at least you still have a usable motor mount to show for it.

Any disadvantages? None I can think of other than the risk that when you go to put the motor mount in, you won't be able to find the **** thing because it got buried under something in the meantime.

So should I do it this way routinely? I usually am not in enough of a hurry that I rush to install the motor mount before its glue dries, and if something goes horribly wrong during my builds, well, it's probably the motor mount, so those aren't particularly significant issues. On the other hand, why not?

Of course, on a TTW fin design, you don't have a choice.

Anyone else routinely do things in a much different order than the usual?

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Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

I RARELY follow the order given in the instructions... I do stuff out of order because doing it right, you can cut a lot of time out of the build... for instance, if I can have the motor mount glued together and drying while the fins are papered and drying and the nosecone CA hardened and being sanded, or parts primered and drying while the motor mount is being glued in or fins glued on, etc...

The instructions USUALLY take NO account of this... that's why I deviate from them. THAT SAID, one must read and fully understand the instructions FIRST, so that there aren't any screw-ups in the build... sometimes there are steps that have to be accomplished first in a particular order, BEFORE some other step later on... and getting them out of order can have MAJOR screw-ups in the build... SO MAKE SURE that there aren't any of these "gotchas" before deviating from the instructions.

Later and good luck! OL JR

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

Well, sure — no sense in standing around while glue dries if there's something else you can be doing. I do that all the time, but something big like not installing the motor mount until virtually everything else is done... that's a new one on me.

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Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

I rarely follow the order in the directions. I usually skip around so I can keep the build going and not sit waiting.

Ah, the dreaded "coke bottle effect"...

If you're getting it, there's two possible causes-- 1) using too much white glue or 2) using wood glue (which shrinks more).

White glue shrinks less, and is better for paper/paper joints like motor mounts (at least in LPR and most MPR using card or fiberboard centering rings inside paper tubes... Low shrink formulas like Titebond Moulding and Trim Glue are another possibility. Yellow glue shrinks SO much that using it to install a motor mount virtually guarantees the "coke bottle effect"...

Hate to say it, but this IS one place where using epoxy is probably the best bet-- for one thing, it "lubricates" the parts as they go together, with no risk of "sticking" or "freezing up" with the parts halfway installed like white glue (when used in small amounts) or wood glue (even when used in larger amounts) can do between tight-fitting paper parts as they smear the glue extremely thin and wick the moisture out of it into the paper parts themselves... Since epoxy doesn't shrink (appreciably) in curing, there should be no coke bottle effect...

I don't mind epoxy for the jobs where it's REALLY an asset; but realistically there's not much that you can't do with white glue and yellow glue, IN THE APPROPRIATE PLACES....

Later! OL JR

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

Just a thought - if the fins are already glued on wouldn't the fin help minimize that problem? The fins would hold the tube and prevent the pull in (except for between the fins)

I jump around as well on the instructions. While waiting for the glue to dry on the motor mount for example, I find that is a good time to put the parachute together, that is unless it is a pre-made one in the Estes kits.

Yeah, I think so... that was my thought on the issue too...

It's the "between the fins" where it'd be more prone to occur then.

Course, don't use too much "shrink prone" (primarily yellow wood glue) and it's not a problem. I had ONE rocket right after I became a BAR with a lot of "coke bottle effect" and that taught me a valuable lesson-- I use wood glue for its higher heat resistance to assemble the motor mount, or rather the rings to the motor tube, areas subject to a lot of heat soak from the burning rocket motor... but to join the centering rings to the tube interior (gluing in the motor mount) I use white glue, and try not to use too much. (since it's sorta shrink prone too in large amounts).

Someone on TRF had an interesting idea-- using Titebond Moulding and Trim Glue (TMTG) to install the motor mounts... that stuff has virtually NO shrink, and therefore, should not cause any coke bottle effect in standard practice. Being thicker, though, I wonder about how well it will spread between parts and any risk of "locking up" halfway through the motor mount installation... I haven't tried it myself would be interested in hearing other's experience with it.

Another option would be Gorilla (urethane) glue... it foams up and expands, but it doesn't rely on moisture evaporation or wicking to cure (quite the opposite-- moisture activates and cures it). It should remain liquid and lubricate the parts going together, and then expand and foam slightly as it dries to lock the parts in place.

later! OL JR

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

Use 15 or 30 min epoxy for ALL motor mounts. No shrink and incredibly strong.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !

The BT needs to be perfectly round if you install fins before the MM. If it has the slightest oval shape, you will end up with crooked fins after installing the MM.

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I love sanding.