Homemade Fin Alignment Guide

Discussion in 'Low Power Rocketry (LPR)' started by qquake2k, Feb 28, 2010.

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  1. Feb 28, 2010 #1

    qquake2k

    qquake2k

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    I "borrowed" Gabe's design for a homemade fin alignment guide, seen here:

    http://gklandes.blogspot.com/2009/02/getting-our-fins-on-straight.html

    I made mine from MDF, and made a couple of changes in the design. I didn't glue the top and bottom together, and used a shim to correct for the fin offset, which was Bravo52's idea. By screwing it together and using various shims, I can use any thickness fin stock.

    fin_guide1.jpg

    fin_guide2.jpg

    fin_guide3.jpg

    fin_guide5.jpg

    fin_guide6.jpg
     
  2. Feb 28, 2010 #2

    qquake2k

    qquake2k

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    More photos.

    fin_guide7.jpg

    fin_guide8.jpg

    fin_guide9.jpg

    fin_guide10.jpg

    fin_guide11.jpg
     
  3. Feb 28, 2010 #3

    qquake2k

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    A couple of things I'm going to change. I don't like the rubber bands, because they "grab" the body tube, and it's difficult to rotate the tube to make minute adjustments. I'm going to use elastic instead. I'm hoping it'll put enough pressure on the tube to hold it in place, and yet allow it to rotate if need be.

    I need to put longer dowels on the bottom, to allow room for the already glued on fins as you rotate the body tube. I had to set it on blocks the first time I used it, when I got to the third fin.

    And I need to find some sort of clamp to hold the fin in place. I just set a heavy battery on it to hold it down, but I want something that puts a little more pressure on it.

    Overall, I'm very pleased with how it works. It's much easier and more accurate than holding the fin in place while the glue sets up. It's a simple yet clever design, one of those "Why didn't I think of that?" designs. Thanks Gabe!

    fin_guide13.jpg

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    fin_guide15.jpg

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    fin_guide17.jpg
     
  4. Feb 28, 2010 #4

    Bravo52

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    Gabe, what about counter-sinking some metal in the fin platform and using a magnet? Just a thought.

    I love this design. It's simple and it works. Now, I also get to "over engineer" and totally screw up the KISS principle it was designed under...... :D


    'Cause that's what we do!:rolleyes:
     
  5. Feb 28, 2010 #5

    tomar

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    I am glad to see you found the flaw in the original design. It may not be a major issue with 3/16" balsa fins, but when you get to 1/4" Birch plywood, it is noticable.

    I mount the jig on the edge of the work bench to allow the fins already attached to hang down out of the way. I've been using this method for about 8 years now with fabulous results.

    I tried mounting the jig on the long end opposite the V so the V was up, but aligning the mark for the fin placement was hard to see as it was on the bottom of the tube.
     
  6. Feb 28, 2010 #6

    qquake2k

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    I think the original designer compensated by making the bottom piece slightly wider than the top piece. You can see it here:

    http://picasaweb.google.com/gklande...djSlmLY&feat=embedwebsite#5300534500323588322

    It was jerry (Bravo52) that came up with the shim idea. I think using shims makes it much more versatile.
     
  7. Mar 5, 2010 #7

    TheAviator

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    I like this design; I think I'm going to make a miniature version for my competition rockets. Heck, my dad probably has enough scrap wood in the basement to make one.

    The only (very very minor) flaw I can see is that you can't do more than four fins, otherwise you start running into the jig. However, that can be easily fixed by trimming the bottom board back at an angle at the fin mount section, so not really a flaw so much as "Hey, I should do that on mine."

    Also, I think rather than screwing mine together, I'm going to use two or three bolts with wing nuts so that the shim can be changed out a little more easily. Also, the extra shims can simply be kept on the the bolts outside of the jig.
     
  8. Mar 8, 2011 #8

    new2hpr

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    With screws or bolts holding the two halves together (with shim in between), how do you guys align the two parts? Do you have dowel pins or hard stops somewhere?

    Neat simple idea. I'd like to make one, at least for little rockets, so more details, please!!

    -Ken
     
  9. Mar 8, 2011 #9

    qquake2k

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    The bolts hold the two halves together in alignment. I didn't use dowel pins or anything else.
     
  10. Mar 8, 2011 #10

    KarlS

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    Instead of rubber bands, how about using 1 inch wide braided nylon elastic? Secure the elastic on the bottom of the jig and use a 3 or 4 inch long strip of hook and loop on the top of the jig with a 1 or 2 inch h&l on the end of elastic.
     
  11. Mar 8, 2011 #11

    AHansom

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    I like the way the rubber band just hooks over the dowels. Looks like its easy to take on and off. Have you tried just putting a small piece of paper between the body tube and rubber band to let it slip?

    Andy
     
  12. Mar 8, 2011 #12

    Fred22

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    Awesome pictures and a great idea:) Simple is good. I think you're on the right track with the elastic idea.
    Cheers
    fred
     
  13. Mar 9, 2011 #13

    qquake2k

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    I wish I could take credit for the idea, but I did take the pictures. LOL

    I've been using elastic for quite some time now, and it works much better than the rubber bands. I use elastic on my bigger fin alignment guide, too.

    vector_force11.jpg

    super_alpha12.jpg

    LOC-IV_build29.jpg

    build34.jpg

    fins4.jpg
     
  14. Mar 9, 2011 #14

    Fred22

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    them are mighty big fins:)
    Cheers
    Fred
     
  15. Mar 9, 2011 #15

    rockets4kids

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    Someone, I believe it was MicroMeister, posted an article about his fin alignment guide for small competition rockets not too long ago. It was the same basic design as this, appeared to be made from 1/4" aluminum plate, and I am guessing that the bevel was cut on a milling machine.

    I assumed the design was unique, and planned to scale it up in pretty much exactly the way shown here. I have a table saw and a bunch of scrap MDF and planned a design pretty much exactly as shown here. It is sure nice to know the jig design scales up and down.

    It seems as if several jigs may actually be in order to work for rockets of differing sizes.
     
  16. Mar 9, 2011 #16

    qquake2k

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    Yeah, that's my LOC-IV and Hyperloc 835. The bigger fin alignment guide works well with 4" body tubes.
     
  17. Mar 9, 2011 #17

    qquake2k

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    I've used my two fin guides with body tubes from 3/4" to 4". I think you'd probably need a bigger one for tubes larger than 4".
     
  18. Mar 9, 2011 #18

    Micromeister

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    Rockets4kids:
    No both the plastic prototype and 1/4" aluminum model were cut on a cheapy B&D bandsaw:) both can handle up to BT-55 dia models.

    I have a larger version made from 3/4" benelex 402, a very dense electrical barrier board, lignin resin cellulose high pressure laminate designed to take & hold precise dimensions despite temp & humidity changes. I was leary of using other woods or MDF bacause of warpage concerns. I've used the larger version on models as large as BT-101 which is very close to 4" diameter with interal mandels and 2" wide leather straps retainers, worked quite well.
    As this thing was always a pretty ugly piece of utility equipment I never thought to take pics of it. Since I've been heavily into MicroMaxing for the last decade or so I'll have to dig it out of the back room and snap a couple.

    Heres a couple of the front & back smaller set-up showing the hold-down strap clamp, the same set-up used in the larger fixture.

    MM Prototype Fin Alignment Jig-a1_Ft & 3 shims_11-16-09.JPG

    MM Prototype Fin Alignment Jig-a2_Bk & Tube straps_11-16-09.JPG

    MM Fin Alignment Jig-b3_Rear view_02-04-11.jpg

    MM Fin Alignment Jig-b7_T-3 3rd fin on (no clamp)_02-04-11.jpg

    Lg Fin Jig-g1_4Pic Page 1of2 11-13- 09_rework-11-05-13.jpg

    Lg Fin Jig-g2_2Pic Page 2of2 11-13- 09_rework-11-05-13.jpg
     
    Last edited: Jan 7, 2015
  19. Mar 10, 2011 #19

    Stymye

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    nice work !
    I would like to see someone come up with a fixture that aligns each fin relative to the other fins , like on a 3 fin rocket and... adjusts for fin thickness.
    I have seen a ton of fixtures that allow the builder to glue a fin on strait , lets be honest ...that doesn't really require a complex fixture.
     
  20. Mar 10, 2011 #20

    rockets4kids

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    As Micromeister pointed out in another thread, the critical issue with mounting fins is getting the vertical alignment perfect. The slightest fraction of a degree off vertical will cause a major performance hit.

    Fins not spaced perfectly even around the BT, or fins whose axis doesn't pass through the centerline cause far less of a performance hit. A few degrees off here will have a negligible effect on performance.

    The design of this jig is to optimize the most critical alignment issue. Just eyeballing the rest is generally good enough. It should be considered an exercise to the reader to extend this jig if that additional functionality is desired. ;-)
     
  21. Mar 10, 2011 #21

    Micromeister

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    Basicly Stymye contest performance doesn't give a rats rosey patutie weather the fins are exactly 90 or 120° apart. That aspect just isn't nearly as critical to peak performance as having them aligned perfectly (or as close as we humans can come) with the centerline direction of travel.

    Art Rose designed and someone is selling a Beautiful precision fin alignment jig that will do both to 1 degree of accuracy between fins while maintaining dead on straight alignment and is adjustable for various fin thicknesses. The jig and 10,13 & 18mm motor mandrels were about 500-600 bucks the last time I looked. Just a little rich for my blood but a beautiful piece of engineering (Photos below)

    A few degrees one way or another between fins make almost no difference in achived altitude but just a fraction of a degree off on a single fin causing the slightest spin can cost 5, 10 or more percent of total achived altitude.
    My concentration when creating models for whatever motor class competition is a total lack of spin. Weather the fins are absolutely evenly space wasn't even really considerd when creating my alignment jig. If spacing were the concern we could just use the old Estes fin jig or simply sight the fins on as has been done for decades.

    FinJig-a1_Art Rose_3C-690x457_350.00_10-07.jpg

    FinJig-a3_Art Rose_Crop2-279x201_10-07.jpg
     
    Last edited: Mar 10, 2011
  22. Dec 3, 2012 #22

    Alpha

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    I was skeptical when I first looked at this thing. I made one this past weekend out of a 2x6 Red Cedar and I am REALLY impressed. I had always just eye-balled the fins and then would sort of watch them on and off as the epoxy dried to make sure they were straight. No more - This thing just works and your fins come out straight as can be.

    I primarily make 2.56 - 4 inch rockets and this jig can handle them all. The posts on the bottom are 4" to be able to easily handle a 4" rocket as the fins are rotated. I used one of the many printed fin alignment guides just to put a mark on the tube where the fin is located. You also need to put a shim between the two big wood pieces which is the same thickness as the fin you are attaching. I just used a couple of spare wood fins which were the same thickness and it worked great! Just put the tube in this jig, wrap the elastic firmly around the tube, epoxy the edge of the fin, clamp it down and see you later.

    I am not easily impressed but this thing works really well and makes fin alignment a snap. I also found a use for the elastic which seems to come in many of my kits..:D Keep it simple!

    Thanks for sharing!

    DSC01911.JPG

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    DSC01913.JPG
     
  23. Dec 4, 2012 #23

    qquake2k

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    As it turns out, the larger of my fin alignment guides works great with 5.5" tubing.

    105_fins.jpg

    106_fins.jpg

    107_fins.jpg

    108_fins.jpg
     
  24. Jan 7, 2015 #24

    K'Tesh

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    Those fin jigs are really impressive! I've gotta get me one of those someday.
     
  25. Jan 8, 2015 #25

    qquake2k

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