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How to use a fin alignment guide

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neil_w

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I feel kinda dumb for asking this, but: how exactly do you use a fin alignment guide, like the kind you'd print from Payload Bay or the Qualman guides or things like that. Particularly with plain old wood glue builds.

Do you tack on all three fins and then slide on the guide? Or do you put the guide onto the BT and then slide the fins into it one at a time?

Now that I'm reading what I just wrote, it sure seems like the second option is the only one that actually makes sense, but I might as well throw the question out there anyway.
 

K'Tesh

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After downloading and printing the guide...

I use a glue stick to glue it to a piece of foam core that I've bought from Dollar Tree (presuming I'm still in the US). I've see people use cardboard too.

Cut out the space for the body tube and the fins, notch the edges for where the fins and body tube meet (don't want to glue the guide to your rocket now do you?).

Slide the guide into place on the rocket. Apply glue to your fin and carefully slide the fin into place... OR... Slide the fin into place, and then tack it down

Repeat until all fins are in place.

Allow the glue to cure.

Then remove guide, and then add fillets.

Since most of my rockets are LPR, I don't bother wasting foamcore by gluing down the entire guide. I just glue down enough to do the job. This means that the part of the guide that tells me that this is a BT-XX for .XXX inch thick fins is often cropped off. So, I'll write the dimensions of the guide down where it won't be removed. Then I can reliably know what the guide is intended for in the future when I want to use it again. I also tend to cut my guides so that 3 fins guides are a clipped triangle, and the 4 fin guides are square. I organize them by the shape, and save myself a moment or two by not having to look through all my guides looking for the BT-XX, 3 or 4 fin guide.
 
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neil_w

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I should try one on my next build. I've been using other methods with good results, but I think this would get my whole complement of fins on in less time.
 

K'Tesh

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I should try one on my next build. I've been using other methods with good results, but I think this would get my whole complement of fins on in less time.
I should have added that it reliably works best with TTW fins. The slot ensures you don't knock the fins around when you are placing your N+1 fin (where N = the number of fins already applied).

And you probably already know not to glue your aft-most CR in place until AFTER you've done your internal fillets. To prevent messing up the outside of the motor tube (thus preventing yourself from sliding the aft CR in place), use a strip of wax paper to prevent the glue/epoxy from coming in contact with it. Also a balloon inflated inside the motor tube prevents glue from creeping inside it.
 
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Exactimator

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I do mine a hair different than K'Tesh.

I have the fin guide prepared as K'Tesh does.
I load up a fin with epoxy
Insert it in the fin slot
Slide the guide over the body tube and fin.
If it's the first fin, I make sure the other fin slots line up with the other fin slots in the guide.
Let the epoxy cure.
Rotate the rocket and repeat the steps.
After the last fin has cured in place, I pull the guide and add the fillets.

If it's a split fin, I only use the guide on the first set. For the second set of fins, I just epoxy the fin in and clamp it to the existing fin with a straight edge (I use a short aluminum level).

I cut the fin slots in the guide a hair narrow (I use cardboard since I''m not as fancy as K'Tesh). That way they sorta grip the fin.

If I put the guide on and try to slide the fins in, I'd get epoxy all over the back of the rocket and make a huge mess.
 

K'Tesh

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I do mine a hair different than K'Tesh.

>snip...

If I put the guide on and try to slide the fins in, I'd get epoxy all over the back of the rocket and make a huge mess.

I should have been clearer... when I said "Apply glue to your fin and carefully slide the fin into place..." I was thinking surface mount.

Exactimator's suggestion about the split fins is spot on. It prevents any chance of a foul up thanks to the imperfections in the guide, then having the guide rotated for some reason.

I forgot to add that I mark a LL line on the guide, and I probably should mark a "front" and "back" for consistency.
 
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Cabernut

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Make sure you cut the cardboard/foamboard exactly 90 degrees perpendicular. Otherwise you might get an unintended cant. I have a bad habit of "leaning" the x-acto when I cut.

I cut one guide exactly the height of the fin placed over the fin tip, and a second at half-height so I can snug it up halfway on the fin to keep them aligned. I suppose if you wanted a cant, then you could rotate one and all fins would be canted equally.
 

kcobbva

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Make sure you cut the cardboard/foamboard exactly 90 degrees perpendicular. Otherwise you might get an unintended cant. I have a bad habit of "leaning" the x-acto when I cut.
+1 !!
 

KidShelleen

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I've used foam board but lately I've been printing them out on 110 card stock and backing it with another piece of 110 card stock. I use a spray adhesive for the bond because it drys fast and won't warp the paper. They are rigid enough and thin so that it doesn't add a cant. I'll then line it up with lines on the BT and use masking tape to hold it in place.
 

Nick@JET

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Make sure you cut the cardboard/foamboard exactly 90 degrees perpendicular. Otherwise you might get an unintended cant. I have a bad habit of "leaning" the x-acto when I cut.

I cut one guide exactly the height of the fin placed over the fin tip, and a second at half-height so I can snug it up halfway on the fin to keep them aligned. I suppose if you wanted a cant, then you could rotate one and all fins would be canted equally.
Using two guides for the front and read of the fun should cure that. Keep these for future builds and you'll start to build a nice stock of fin jugs!
 

K'Tesh

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Make sure you cut the cardboard/foamboard exactly 90 degrees perpendicular. Otherwise you might get an unintended cant. I have a bad habit of "leaning" the x-acto when I cut.

I cut one guide exactly the height of the fin placed over the fin tip, and a second at half-height so I can snug it up halfway on the fin to keep them aligned. I suppose if you wanted a cant, then you could rotate one and all fins would be canted equally.
Of course, the fin canting problem is for surface mounted fins. It's a lot less of a problem when the fins are locked in place by TTW tabs.
 

Banzai88

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I cut the corners of the jig where the fin meets the body tube to reduce the risk of gluing the jig to the rocket or the fins. :facepalm:
 

K'Tesh

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I cut the corners of the jig where the fin meets the body tube to reduce the risk of gluing the jig to the rocket or the fins. :facepalm:
It's been mentioned... And I noticed that my Cherokee D guide (in the photo) didn't have the clipped corners. That was one of (if not my) first guides. However, with TTW, it's not so much of a problem if you are only tacking the fin to the MMT (and maybe the front and back edges of the root edge). Once the tack is done, you can do the internal fillets, then remove the guide for the external fillets. Still, clipping is a good idea.
 
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