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APRO Lander II Build Thread

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neil_w

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OK, let's get this party started.

Background (even though no one cares)

First time I laid eyes on Gary Byrum's (first) APRO Lander I fell in love with the design, and decided to build my own version of it, despite my trepidation at dealing with those gigantic transitions (prior to this build I had never rolled a single paper shroud). Later when Gary built another one I paid close attention and learned what I could.

When I started to prepare for the Biohazard build, I decided to get my fins laser cut. Well, there was a minimum charge, and the Biohazard parts were going to be way under the minimum, so I (not so) hastily pulled together my APRO design (which I am creatively naming "APRO Lander II"), and got that balsa done at the same time. The fact that I got the wood laser cut for this rocket had a big influence on its construction, because I could never have done what I did with hand cutting (as you'll see).

I have been nervous about starting this build because there are so many ways for me to screw it up. But now that Biohazard is finished, I guess I can't put it off any longer.

I promise there will be at least a few interesting and/or odd things in this build. :)

Here's the design I ended up with: it's a bit different on the outside, and wildly different on the inside. ORK file is attached at the bottom.

Render:


Side View from OR:


The most immediately obvious difference (other than the fin design, which is mostly cosmetic) is that I run my BT80 all the way to the back of the rocket, and mount the fins to it, rather than the BT55 in the center. I did that because I thought it would ultimately be a bit easier, with smaller fins and less total surface area for the big centering ring (that's a 6" diameter ring) in the back.

ORK file:
View attachment lander.ork
 

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neil_w

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Long before I actually started building this thing, I figured I could try to fabricate the transitions. If I couldn't come up with some decent ones, then no point in continuing. And really, it's the big one that is the most critical.

The template comes out to a bit under 9x14":
large_shroud.jpg

Finding something officially labeled "card stock" at that size was fruitless, at least in any store I could find locally. Finally, following Gary's advice, I nabbed a pack of 14x22" poster board from Walmart. I think it was this, although I can't seem to find my pack of it right now: https://www.walmart.com/ip/UCreate-Poster-Board-14-x-22-8pk/17203958. Of course there is no weight listed on the package (or online), so I just tried to gauge it by feel, and ensure that it was more than 65 lb. I really have no idea of its actual weight. It also has one shiny side, which I figure should go on the outside, but who knows.

For my first attempt, I cut the join tab as a separate piece and glued it to the inside. Failure. The stiffness of the two layers of poster board meant that the seam area wouldn't bend well. That one was so horrible I tossed it without taking a picture. But I learned.

So for the next one I just went with the standard overlapping tab. I followed Gary's strategy of rubber-banding the paper into a tight cone to put some curve in it before gluing:
pre-curled_transition.jpg

Then I had to figure out how to actually hold the thing in position while the glue was setting. I took two pieces of wood strip, rounded them off so there would be no sharp edges to dig in and mark the paper, and fashioned a crazy clamp setup:
apro_build_trans - 2.jpg

There is probably a simpler way to do it, but this arrangement worked pretty well, once I went through the juggling act of getting the wet-glued transition into the clamp. I Bondo'ed the seam (first time using Bondo), which came out "OK"; the seam will be visible on the finished model, but I'll live with that. After getting this one done, the other two transitions were straightforward.

This photo gives some perspective on the size of this transition:
apro_build_trans - 1.jpg

This was all done months ago, then my whole workbench got packed up and a major home remodeling project got underway, and I focused my efforts on finishing up Biohazard. But I had passed my major first test, and knew that this build could go forward... eventually.

Oh, one more detail: no centering rings have been installed in these transitions. This build will take a different approach. Because my BT80 extends all the way through the transition, I didn't need a 55/80 ring in the front of it (it'll just slip right over the BT80), and as for the back... well that will wait for the next update.
 

Gary Byrum

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When I do those big shrouds, I try to get the roundness as close as possible to where the gluing takes place. Once I get the tab glued in position, I take a 1/2" dowel and run it through, placing the glue joint down on the cutting mat/table, and apply even pressure all the way across the joint. Once I am satisfied with a level of adhesion, I use the dowel with shroud in hand, and form the glue joint so it has a bend/curve in it. I really don't like for that to be flat because it's stands out and is totally obvious. Basically, the glue joint is workable when it's about 1/2 dry. Totally hardened joints are nearly impossible to curve. You can still manipulate the curve with your fingers so it matches up with the roundness of the shroud as long as it's not completely dry.
 

TangoJuliet

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Neil - I've often wondered, when other modelers say to use "card stock", just what is card stock and how is it identified?

Gary - Any chance of providing a video of your method? I think I understand your description, but a video would certainly solidify it in my mind.
 

neil_w

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Neil - I've often wondered, when other modelers say to use "card stock", just what is card stock and how is it identified?
Typically it is labeled as cardstock, e.g.: http://www.michaels.com/paper/cardstock-paper/809188528. It is simply very heavy paper. 65 lb is light, 110 lb is heavy.

Then there is "poster board" (like I used) which is pretty close to the same thing but not labeled with a weight. Again, it's basically just heavy paper.

Ultimately, my search was for large-format, heavy paper. I did *not* find anything actually labeled "cardstock" that suited my needs.
 

Gary Byrum

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Card stock can be bought in different weights at office supply stores and such. 65# 110# is what I have on hand. 65# is standard card stock and works well for most models. 110# is thicker and makes for a really sturdy standard shroud for most LPR models. 8.5 x 11" isn't big enough for something like Neil's Lander, so he needed a poster size board. Unfortunately, they aren't always sold in reference to #'s or lbs, if you will. That's when you take your 110# scrap to wally world with you and find something thicker that just feels right for the job.

Tango, I don't have such a video, but I did order me a new camera this morning, so after I learn how to run it, I'll try to remember to video something for you. You should be able to get a fairly good mental picture from my instructions above though. I try to get the glue joint close as possible before gluing so there will be little to no tension tugging at it. Laying it on a flat surface helps distribute even weight when using the dowel and insuring an even glue joint. Always check for small gaps on the edges though. Sometimes you can miss a place when applying the glue and you'll want to fix that before you finish.
 

neil_w

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When I do those big shrouds, I try to get the roundness as close as possible to where the gluing takes place. Once I get the tab glued in position, I take a 1/2" dowel and run it through, placing the glue joint down on the cutting mat/table, and apply even pressure all the way across the joint. Once I am satisfied with a level of adhesion, I use the dowel with shroud in hand, and form the glue joint so it has a bend/curve in it. I really don't like for that to be flat because it's stands out and is totally obvious. Basically, the glue joint is workable when it's about 1/2 dry. Totally hardened joints are nearly impossible to curve. You can still manipulate the curve with your fingers so it matches up with the roundness of the shroud as long as it's not completely dry.
Shaping the joint while 1/2 dry is a good idea, it didn't occur to me to try that. I ended up with a good curve at the joint, but the whole thing is definitely not as perfectly clean as I would like, and *will* be visible.

What I really wish I had done was put the joint right at a fin cutout, so most of the joint would have ended up completely removed from the model; in that case I would have done a few things differently like I would have made the tab smaller up top and wouldn't have Bondo'ed the whole joint. I'm actually getting more tempted to go back and do it this way, but I can't decide if I want to deal with that darned thing again, since my current part is basically perfect apart from the seam (although that's a pretty big "apart from"). Hmm, maybe I'll give it a try, and if I screw it up I can just use the transition I already have. Will think on this.
 

Gary Byrum

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Shaping the joint while 1/2 dry is a good idea, it didn't occur to me to try that. I ended up with a good curve at the joint, but the whole thing is definitely not as perfectly clean as I would like, and *will* be visible.

What I really wish I had done was put the joint right at a fin cutout, so most of the joint would have ended up completely removed from the model; in that case I would have done a few things differently like I would have made the tab smaller up top and wouldn't have Bondo'ed the whole joint. I'm actually getting more tempted to go back and do it this way, but I can't decide if I want to deal with that darned thing again, since my current part is basically perfect apart from the seam (although that's a pretty big "apart from"). Hmm, maybe I'll give it a try, and if I screw it up I can just use the transition I already have. Will think on this.
Consider it good practice. Make another one if you want to. Here's another thing to consider. Since I didn't CA treat the shroud, I did CA the joint area. This allowed me to sand down that hideous edge. It'll always look like a bump even if you Bondo it so, get rid of it as much as possible. Then a little Bondo will even things out.

Fortunately, I did consider the joint area for fin placement in my build.
 

neil_w

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Consider it good practice. Make another one if you want to.
I think at this point I can hardly justify not trying. It costs me nothing but a bit of effort, and I always have the existing part in-hand as backup. It'll be a while before this blocks me from continuing, so I have time to give it a whirl.

Here's another thing to consider. Since I didn't CA treat the shroud, I did CA the joint area. This allowed me to sand down that hideous edge. It'll always look like a bump even if you Bondo it so, get rid of it as much as possible. Then a little Bondo will even things out.
Another great idea that I will try. On the big one I'll do all the seam smoothing after I cut out the fin slot, so I won't waste my time on any part of the seam what will later be removed.
 

Gary Byrum

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On the big one I'll do all the seam smoothing after I cut out the fin slot, so I won't waste my time on any part of the seam what will later be removed.
Hmmmm....Really? Seems to me that it would be easier to sand the whole thing first (no slot to dodge) and easier to cut out the slot having sanded the CA away. CA can be a little hard to cut. Especially on something like this. Your choice though.
 

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Hmmmm....Really? Seems to me that it would be easier to sand the whole thing first (no slot to dodge) and easier to cut out the slot having sanded the CA away. CA can be a little hard to cut. Especially on something like this. Your choice though.
I meant that I wouldn't do any of it, including applying the CA, until after the slot is cut. True that sanding could be easier without working around the cut, but then there'd also be a lot less seam to sand, so.... Will see how it goes.
 

neil_w

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Found it! This is the stuff I'm using:
ImageUploadedByRocketry Forum1478117631.278405.jpg
 
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neil_w

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New edition of the big transition in progress:
ImageUploadedByRocketry Forum1478121925.572671.jpg

The overall quality of the cutout on this one is *much* better than the last one. You can see the funky tab, exposed on the front. The tab on the large side of the transition is only 1/8" wide, so it'll be completely cut out as a fin slot. The bottom part is 1/4", which is pretty skinny; we'll see if it ends up being enough. Given the number of different ways this transition will be held together I think it'll be OK.

This time, after fumbling with the rubber bands, I decided to just Scotch tape the transition into its over-curled shape. The tape will hold it in perfect alignment, and removes easily off the glossy outer surface. I hope I didn't actually damage the paper while fumbling with the rubber bands, but we'll see. I may actually try to use the tape to hold the transition together while drying, but I'm not really sure if it'll work properly for that.

I'll probably re-fabricate the other two transitions as well, but won't talk about it unless something particularly interesting comes up.

Now, on to other parts of the build.

[edit] Argh, I just realized that measuring for the cuts in the transition was much easier before certain other construction tasks were completed. I was able to make the cuts absolutely 100% perfect. Now it's going to take a lot more work. Maybe I can use the old transition as a template to mark the cut lines on the new one, we'll see.
 
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neil_w

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Now let's get to the first odd and (hopefully) interesting part of the build.

Between the two large transitions goes a large centering ring, which goes from BT80 to 6". For a whole host of reasons, including my lack of optimism about being able to cut one of high quality, my desire for it to be strong, my desire for it to provide a good anchor for both transitions, and last but definitely not least my imminent laser-cutting order, I decided to build the centering ring out of 1/8" balsa. To fit it into the sheet I was cutting, I laid it out in four pieces, with alternating grain direction, like so:
apro_build_ring - 1.jpg

The holes in the pieces are there to cut down weight and also make the inside of the transition(s) accessible during assembly. I thought the strength would still be OK, but honestly I was wild guessing about how large I could safely make the holes. I honestly had no idea if this would work out at all, but it seemed like a fun thing to try (on that count I was correct :)).

The grain direction is not ideal but I figured that by having each piece at 90 degrees to the adjacent one, they'd lend each other strength. Also note the launch lug cutouts; I got two copies of each of two pieces, so that's why there's two. One will go unused.

I glued them together...
apro_build_ring - 2.jpg

And it didn't feel quite as stiff as I would like. So you know the next step:
apro_build_ring - 3.jpg

A nice messy papering job, with some space left around the edges so there'd be room for the transition to glue completely to the wood instead of the paper. I'm really getting good at this, sanding the paper out of the eight holes only took a few minutes (sloshing the wood glue around all the edges took longer). I don't really know if the paper added that much strength but I figured it had to help at least a little. The whole thing felt fine when finished. In hindsight I shouldn't have really worried so much about the strength (probably didn't need the paper) as we'll see later.

Finally, before gluing the ring to the BT80, I attached the rear supports to the ring. These pieces go behind the ring and are intended to support the rear transition. Having these pre-attached to the ring would, I figured, make it easier to position the ring accurately on the tube later on (with the supports lined up with the end of the tube).
apro_build_ring - 4.jpg

In the above picture the tube is not glued to anything, it's just there to provide a reference position for the other parts to ensure proper position and alignment.

There's still more work to be done with it, but at this point I considered my crazy balsa centering ring to be a success. Were it not for the laser cutting I would never have attempted such a thing.
 
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Looks like it's off to a good start. That centering ring is a good example of the benefit of laser-cut.
 

neil_w

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Looks like it's off to a good start. That centering ring is a good example of the benefit of laser-cut.
Indeed. I *so* wish I had regular access to a cutter, rather than needing to farm out the jobs.
 

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Very cool, Neil (and Gary)! I like how it's different. Kinda reminds me of a flying Mercury capsule!

Some things that've helped me with transitions.
  • marking alignment & fin positions/slots when the cardstock is flat.
  • aligning the joint edge to one of the fin positions.
  • pre-curling them tighter than the final curl so that they keep their shape on their own. my challenge is trying not to crease it while doing this.
  • gluing the internal tab to the one of the transition edges first rather than to both at the same time; temporarily taping the transition together for overlap joints.
  • using double glue joints on the tab & mating surface (hence needing to position everything correctly first with tape, etc): apply glue to surfaces, let dry, fix position, apply 2nd glue layer, align, & burnish.
  • cutting fin slots with scissors after the transition is glued & shaped (if the slots reach one of the ends); otherwise use a hobby knife / box cutter.
  • if using white glue, the hair dryer does wonders for heating & reshaping the glued joint.
  • if attaching other things to the top or bottom, leave extra finger tabs to cut & fold in as extra mating surfaces. Or just add extra paper/cardstock tabs.
I really wish I had access to a laser cutter as well. It would've made my Starfury build much easier.
I'm looking forward to the progress & the finished project! :)
 

neil_w

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Some things that've helped me with transitions.
Dude, not cool! Posting all these helpful tips right after I've fabricated my third set of transitions! :bangpan: (j/k)

I am happy to say that I figured out at least some of these on my third go-round; some others don't apply here. A few require comment:
  • aligning the joint edge to one of the fin positions.
I realized after my last exchange with Gary that I could cover almost *all* my seams with fins on this model. The front and rear transitions therefore will require no Bondo whatsoever. The big transition in the middle will have 2/3 of its seam completely removed; the rest needs to be smoothed but that's a huge simplification from what I had before (and I did the CA+sand the seam before Bondo, so that whole thing should come out *way* better this time).

  • pre-curling them tighter than the final curl so that they keep their shape on their own. my challenge is trying not to crease it while doing this.
I've had some problem with creasing on the inner edge of these (with this heavy poster board). We'll see how it looks when finished. The front transition, which is small and run-of-the-mill compared to the others, I might make re-fabricate (yet again) out of garden-variety card stock, which I now suspect would be pretty easy for me to do.

  • if attaching other things to the top or bottom, leave extra finger tabs to cut & fold in as extra mating surfaces. Or just add extra paper/cardstock tabs.
Now that is something I had never thought of. I'm not sure if I have a good way to take advantage of this right not but I'm going to have to keep it in mind.

Thanks for the input!
 

neil_w

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Argh. I was going to post a picture of my freshly 3D-printed part so you could all guess what it is. But there was a problem printing, so it's actually not ready yet. I'll probably get the finished piece on Monday.

But because I was all psyched up to post the picture, I can't wait until then. So here's a few different viewing angles looking at it in the CAD software. Can anyone guess where it goes, and what is its purpose? It's not in the OR file, but by looking at the OR side view (posted at the beginning of this thread) you might be able to come up with a reasonable guess.

It'll be a little while until I'm actually ready to use this part, but I am eager to get it into my grubby little hands.



part_views.jpg
 

Gary Byrum

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Looks like some sort of launch lug gizmo. Or a f***ed up funnel with an unknown purpose.
 

neil_w

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Looks like some sort of launch lug gizmo. Or a f***ed up funnel with an unknown purpose.
On the right track with the first guess. I'll just leave it out there for now.


So I cut and fit my new large transition, and indeed it was much harder to do accurately with part of the assembly already completed (haven't yet covered this in the build thread, will get to it). I think I got it good, and overall it fits well. Compared to the first one, it does have a bit of creasing in a few places at the front (the old one was almost perfect in this regard) but the new one will have *so* much less ugly seam showing, that it still seems like a net win. I don't think I'm up for making yet another one.

The new rear transition looks perfect. The front transition will probably be replaced, since the front hole is a bit too small and anyway it's a bit more creased than I'd like. Fortunately I don't need that one for a while so I can fiddle, and it's a relatively easy one to make anyway.
 

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Dude, not cool! Posting all these helpful tips right after I've fabricated my third set of transitions! :bangpan: (j/k)
Oops! Sorry about the timing! :facepalm: It sounds like you've got a good handle on the situation though! :)

Argh. I was going to post a picture of my freshly 3D-printed part so you could all guess what it is.
Internal launch lug at the top of the big transition? Flush cut with the front shroud angle, and open funnel at the back to guide the rod inserted from the aft lug? Avoids using a really long lug, and helps prevent the rod from wandering & damaging the shroud from the inside? :)
 

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Oops! Sorry about the timing! :facepalm: It sounds like you've got a good handle on the situation though! :)


Internal launch lug at the top of the big transition? Flush cut with the front shroud angle, and open funnel at the back to guide the rod inserted from the aft lug? Avoids using a really long lug, and helps prevent the rod from wandering & damaging the shroud from the inside? :)
Would have been a whole lot less expensive using the canned foam and customizing the fit for said lug. Something I wish I had done on my Tikk Takk rocket. The internal rod damage it has acquired, gave me the foam concept.
 

neil_w

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Internal launch lug at the top of the big transition? Flush cut with the front shroud angle, and open funnel at the back to guide the rod inserted from the aft lug? Avoids using a really long lug, and helps prevent the rod from wandering & damaging the shroud from the inside? :)
Well played sir. 100% correct and complete and nothing really for me to add, other than I hope I made it big enough. You win a cookie. :)

Oh, I call it the "rod catcher".

Gary Byrum said:
Would have been a whole lot less expensive using the canned foam and customizing the fit for said lug.

It's actually quite inexpensive if you group a few jobs together to dilute the setup cost (which is about $5), but that's not the point anyway. I find designing a part and 3D printing it to be just about the most geeky fun I can have, so I'll go out of my way to come up with 3D printed solutions to things. I just hope it works OK.
 

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It's actually quite inexpensive if you group a few jobs together to dilute the setup cost (which is about $5), but that's not the point anyway. I find designing a part and 3D printing it to be just about the most geeky fun I can have, so I'll go out of my way to come up with 3D printed solutions to things. I just hope it works OK.
I'm certain you won't regret having installed it. In fact, it's quite genius. And if you knew what a PIA it is trying to fit 1 long lug through there, you'll be glad you didn't have to do it.
 

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I also neglected to mention previously that another reason I extended the BT80 all the way to the back was to provide a good lug platform, with less obstacles to thread the launch rod through.
 

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Let's get back to building, shall we?

First I glued the ring to the end of the BT80 (with the support fins flush with the end). Then I market the four fin positions on the BT80, using the seams in the centering ring as my markers. Then a dry fit:

fin_assembly - 1.jpg

I marked the fin lines using the lines on the BT80 and the seams at the edge of the centering ring (those seams sure came in handy). I needed about 3" of slot on the transition to let the fins through, so I cut them out accordingly, making them just a bit wider than 1/8". I debated a *long time* whether I should first glue the transition in and then cut the slots (and then insert the fins, the way Gary did) or if I should cut the slots first, which was my original plan. I eventually decided to stick with my plan. So I cut the slots:
fin_assembly - 2.jpg

...and the whole thing seemed to be holding together just fine. Whew.

Now it's time for the fins. *Of course* I papered them, and when finished they looked like this:
fin_assembly - 4.jpg

The funny fin shape was another benefit of laser cutting (I would have had a hard time hand-cutting those); you can see the reason for the shape in the original side view or, even better, in this picture:
fin_assembly - 3.jpg

The fins glue both the the BT and to the ring, and form a very strong structure. This is why I probably didn't need to paper the ring; once the fins are attached the whole structure is very solid. And it looks like this:
fin_assembly - 5.jpg

And then of course I had to test-fit the transition over it, and boy howdy everything looks great!
fin_assembly - 6.jpg

I was still not thrilled with the solidity (or lack thereof) of the transition in the areas between the fins. It felt like I was likely to destroy the whole thing when sanding the primer. So I hand-cut some spars out of 1/16" balsa and glued them in between the fins, like so:
fin_assembly - 7.jpg

There are two spars between the fins on the left, because that's where the launch lug will go, so I couldn't put one spar in the center; instead I put one on either side of where the lug will go (leaving adequate space, I hope, for the rod catcher).

Looking pretty good so far I think.

[note 1: these pics all show my 2nd transition, which I've pretty much decided not to use, in favor of my 3rd one, as discussed previously. Most of the same steps applied to the fitting and cutting of the third one, except I had to do it after the fins were glued in, which made marking the fin lines a bit more tricky.]

[note 2: the seams on the ring made perfect alignment marks for the fins. Each fin is perfectly centered on a seam and the line on the BT, which is drawn from the seam. No fin jig needed on this build, and the fins are dead-nuts straight]
 
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