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Getting the fins on straight?

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jqavins

Joseph Avins
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So you keep the cheaper on and apply fillets over it?
Yeah, the cheapers cheaters are sometimes called balsa fillets. Cheaters for positioning, balsa fillets for strength, but it's basically the same thing either way. BABAR is a big proponent of both.
 

afadeev

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You can eyeball them well enough. Not all of us can. A builder's got to know his limitations (and use tools to compensate).
"well enough" is in the eye of the beholder.
Unless you glue the fin at 10+degree angle from running along the longitude of the airframe, it's "good enough". The rocket will fly, and will fly fairly straight. It might rotate a lot, but that will only aid stability.

Even if your fins are not perpendicular to the airframe, it will still fly perfectly fine. It may look a bit crocked, from certain angles, but it will fly straight.

The rest is just the degree of perfection, and some care about that more than others.
Some folks just want to improve their building skills, even if they don't produce appreciable flying improvements. Which is perfectly fine, and enjoyable in its own way. I like to challenge myself to get the fins perfectly airfoiled, and mounted perfectly straight.

If and when you get there, a proper fin alignment jig (Estes gizmo doesn't qualify) that both holds the rocket airframe and the fin in the desired fixed position, is the way to go.

IMHO,
a
 
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dr wogz

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yeah, one caveat about the Estes style jig, is that is it calibrated for one fin thickness.

Say, it's design for most of Estes kits, which are 1/8" thick balsa fins. That means the fin-holder part and the slots it slides into is half the fin thickness; offset by 1/16", to allow the fin to be centered on the tube.

When yo move up to a 1/4" thick fin (Exaggerated, but to make the point) the fin would be 1/16" on one side of the center, and 3/16" on the other.. Realistically, it'll only be offset by a 1/32" or 1/64".. but the point is, it's designed for only one fin thickness.
 

jqavins

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yeah, one caveat about the Estes style jig, is that is it calibrated for one fin thickness.
Almost right. The flat panels are slightly offset from the center of the flange that slides into the base, so the active face is offset by 1/16" if you slide the panel in one way (for 1/8" fins) and by (I think) 3/64" if you slide it in the other way (for 3/32" fins). Or it may be the second side is for thicker, 3/16" fins, rather than thinner 3/32". The panels are marked on both sides.

So you're right, it's not as general. Two sizes is a good deal better than one, yet still leaves plenty to be desired. And it's only designed for 13, 18, and 24 mm motor mounts, so you have to find or make adapters for other sizes.

It gets the job done on nearly all LP builds, and I absolutely love it.
 

dr wogz

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I remember wanting one when I was much younger, but have managed well without.

One thing I do find funny, is the FB posts of people gluing fins on, and seem to have everything precariously balanced on stuff. Namely the BT balanced on a rocket holder or cradle, and the fin positioned between two "things" to maintain vertical..

What ever happened to sandwiching the BT between two books on the work surface? And oriented so you can sight down the length of the BT to get the fins on straight..
 

BABAR

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So you keep the cheaper on and apply fillets over it?
Yup. Some may not like the cosmetics. A “structural” glue fillet, meaning only the amount of glue required to improve structural integrity won’t hide it, but a thicker “cosmetic” fillet would hide them.

I used them on my Tank Killer,

You can see them at the base of the rocket (they were waaay too long, extending far forward of the fins, but turned out nice for demo purposes, and for that rocket “cosmetic” wasn’t an issue.)

That bird flew absolutely straight, essentially ZERO roll. Kinda like the Skelenut from @gfunk
Not that he used balsa fillets, to my knowledge

Great video, cut to 2 minutes to show the rocket (bone?) solid stability
 

rharshberger

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My two most common fin jigs...
The wood one made from scrap pieces of 18mm baltic birch, uses fin thickness shims between the two angled boards to set centerline, easy to use and can be rotated so fin being glued on is laying flat, the tube is rubber banded to the jig using the posts on both sides of the angled boards, this style jig has been around TRF and other sources for a long time.
20200910_132648.jpg

20200910_132654.jpg

20200910_132701.jpg
Butterfly Fin Jig, the laser cut plywood pieces hold two aluminum angles and work just like the wood fin jig above. The Butterfly Fin Jigs were given to me by a TRF'er @wcravens who's design they are, here is the thread about them.... https://www.rocketryforum.com/threads/free-butterfly-fins-limited-offer.129885/
They get a lot of use when building models in my fleet.
20200910_132718.jpg
 

gna

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What I really wanted to comment on was your cat.
I like dogs but right now I have cats. They are my children. I have one that can be a little annoying when I'm trying to build rockets. My parents had one that looked like yours. Gone many years now.
He is ROCKET CAT.
IMG_2922.jpg

Here he's all worn out after helping repair my Leviathan.
 

jrap330

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Yup. Some may not like the cosmetics. A “structural” glue fillet, meaning only the amount of glue required to improve structural integrity won’t hide it, but a thicker “cosmetic” fillet would hide them.

I used them on my Tank Killer,

You can see them at the base of the rocket (they were waaay too long, extending far forward of the fins, but turned out nice for demo purposes, and for that rocket “cosmetic” wasn’t an issue.)

That bird flew absolutely straight, essentially ZERO roll. Kinda like the Skelenut from @gfunk
Not that he used balsa fillets, to my knowledge

Great video, cut to 2 minutes to show the rocket (bone?) solid stability
Amazing, flew straight, no role. Really did not see the cheaters. But, I think I would have to really embellish the fillet to hide it...but it adds strength. Great
 

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Amazing, flew straight, no role. Really did not see the cheaters. But, I think I would have to really embellish the fillet to hide it...but it adds strength. Great
Or paint it a contrasting color, or stick paper or plastics straws over them for mock laser cannons!
 

jqavins

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RobertH3 posted this tip for sourcing 1/2 round strips to put on fin edges. And they also have cove molding, which could make a cheater that's much easier to hide under a cosmetic fillet. And even easier if you do a little sanding first on the flat faces. Or you could sand the square strips on one corner to make triangles, without touching the business faces. (Can you buy triangular strips like that?)
 

beeblebrox

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3D printed centering rings are the easiest way to do it. Alignment is near perfect. (Assuming the fins are thru the wall to a smaller diameter motor mount tube.) Surface mounted fins are not good. (Thru the paint) A 3D printed guide that slips on the outside of the tube works well too. Also if you must do surface mount fins, I.E. minimum diameter, super glue is your best friend, use it to tack the fin on place, then epoxy fillet it later for strength. If you don't have a 3D printer, PM me, perhaps I could make you something for a very reasonable price. (5.5" or less tube sizes for now)
 

jqavins

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If it's through the wall fins, centering rings with alignment notches can also be cut from wood, by hand or by laser just as well as they can be 3D printed. It's a matter of what tools one is most comfortable with and has available.
 

JLP1

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Hi All,

So I built one of Macklin's guillotine fin jigs to do the fins on my new LOC-lV and for some reason I can't seem to master it. I read and reread the instructions and I must be missing something. You can see in the first pic (jig2) the fin is in place and everything is set up and you can see that the body tube appears to be off. I have a small level that I can place on the fin between the BT and the bottom of the angle and the bubble is dead smack in the middle. Can't tell if it's just my eyes playing tricks or if it's really off. The second pic shows where I backed off the angle, kept the top fin in the groove and placed the remaining fins in the tube using just the MK-1 eyeball for alignment and you can see it looks a lot different. Had no problems building the jig it's true and square (really nice woodwork). Either I'm just missing something or I need new glasses. Any Ideas?
 

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jqavins

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Can't tell. It looks from here like neither picture is taken dead-on square to the jig; jig3 is close, and jig2 isn't. It's really impossible to say if anything in jig2 is straight because the picture is so far from straight.

Also, they both need more light inside the tube; they're pretty nearly black holes. Maybe take pictures with the room lights off and at night, so the auto exposure is responding only to the light coming back from the flash.

I'm not trying to be a photography critic, it's just that I can't see what you want seen.
 

dr wogz

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Yeah, it looks off to me too. Maybe do my trick, and see where your aluminum angles lay..

(Spent motor case, with a rod running thru it's diameter: see post #3)
 

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JLP1, are you also drawing lines on the tube as a backup ?
If not do that also. I don’t let the top section come down tight on the Tube. I can still turn the tube.
I happen to have a Starrett square. So I also carefully bring lines to the edge of the tube. When all is setup, the square is my indexer. Adjust tube to agree then use drawn lines to check fin fit. Also the square is eyeballed to the fin.
So far so good, but have only used bit once , and it’s the smaller version.
Yes I’m his neighbor, but disclosing I paid the same for mine minus shipping

the aluminum jig above I think is thebest type. Shim material is easily avail in many thicknesses. One day I will make one on the mill. For the center post , a local hobby machinist can make perfect fitting cylinders for any tube size at reasonable costs... I would think.
 

JLP1

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Yep I should have gotten the camera a little more squared up. The pictures are lighter here and they darken up with the posting but if you click on them they will enlarge and you can see it better.

Nope I haven't drawn any lines on the tube I'll have to figure out how that would work? Are the lines drawn from the center of the slot? I know that when I square the angles up it measures 2-11/32" from the edge of the angle to the edge of the sliding panel on all four corners. So that should be telling me that the angles are aligned with the BT. It's a fine jig and the quality of the wood, parts, and fitment are 5 stars. I just thing the operator is a one star (that's me) 🙂
 

XrayLizard

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Just the same lines one would draw on the BT, with a piece of angle aluminum representing the the fin locations, alignment
 

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I have had good results with the Estes tube marking set. Love the base for laying out the fin spacing. Also I sometimes use pieces of wall molding material notched big enough for the fin thickness to hold them in place while the glue sets.
 

dhbarr

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So I built one of Macklin's guillotine fin jigs to do the fins on my new LOC-lV and for some reason I can't seem to master it. I read and reread the instructions and I must be missing something. You can see in the first pic (jig2) the fin is in place and everything is set up and you can see that the body tube appears to be off. I have a small level that I can place on the fin between the BT and the bottom of the angle and the bubble is dead smack in the middle. Can't tell if it's just my eyes playing tricks or if it's really off. The second pic shows where I backed off the angle, kept the top fin in the groove and placed the remaining fins in the tube using just the MK-1 eyeball for alignment and you can see it looks a lot different. Had no problems building the jig it's true and square (really nice woodwork). Either I'm just missing something or I need new glasses. Any Ideas?
Do you have a same-thickness piece of fin-material in the other end of the aluminum angles ?
 

JLP1

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Yep 1/8" ply just like what the fins are made out of. I did notice last night that when I tighten the nuts on the angles to hold the fins in place that the tops of the angle spreads wider. This lessens the point of contact between the fin and the angles so instead of holding the fin securely they are really just pinching the fins in one small area across the face of the fin. So I think I still need to do some fine tuning on the jig. I also printed an alignment tool from payload bay last night I'm going to mount that on some form board and compare the two. I went over how I built the Macklin fixture last night and I don't see any obvious mistakes it's a pretty straight forward build. The only thing I noticed was that the instructions state that the fits would be snug and a mallet might be required to assemble but mine just slipped right together. The base sets level doesn't rock or binds so that's where I'm at today. I watched (2) videos yesterday on using the jig and I think I'm doing everything right the only difference in what I'm doing and what Macklin and Van Milligan were doing is that they were installing surface mount fins and I'm doing thru the wall motor mount fins.

Cheers 🙂
 

Ian A Dalton

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Actually, this is the best you can buy. Also the easiest to use and the fastest jig on the market.
 

dr wogz

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it's one thing to have the tool, it's another to know how to use it!

(like, people who get a jeep, then get it stuck.. "But it has 4-wheel drive!")
 

XrayLizard

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Doing fins tonight
I have drawn lines like one would do with any kit to align fins.

but this time I drew the fin lines to extend forward past the scrap piece.

so now I can more easily see the overall alignment. The scrap is centered , the fin looks centered.
Also use the lines to view the line intersection of the v cutouts when initially setting up.

two more fins for the results!

ps noted that my aluminum angles do not. Seem to open up at top
 

BABAR

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it's one thing to have the tool, it's another to know how to use it!

(like, people who get a jeep, then get it stuck.. "But it has 4-wheel drive!")
Sort of like the once a decade iced up freeways in San Antonio.

“How’d I end up in this ditch? My car CAN’T slide, it has 4WD!”
 

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