Fin Allignment Jig --- Build Thread

A fin alignment jig good for 2" - 5" BT's. Used to properly align fins against BT when gluing. You can also hang the fins off the opposite end to aid in making nice fin fillets. Pictured below is the jig holding an already finished rocket (you should be able to get the concept). My 3" build parts are scheduled to deliver on Tuesday so within a week or so will post some pics of the jig in actual use gluing fins to the BT.



Parts List:

32" of 2x6 -- dry, straightest, flattest board you can find
8" of 2x4
2x --- 1/4" x 5" eye bolt
4x --- 1/4" washers
2x --- 1/4" wing nuts
8x --- small hook eyes
4x --- 2 1/2" wood screws
36" of 1/4" flat elastic (or similar from an old rocket kit )
1 sheet sticky backed craft felt
2x --- wood shims same thickness as fins -- approximately 12" x 1"

They say a picture is worth a thousand words so just follow the pictures. All critical information is in the pictures.

Not sure if I can finish the build thread tonight but if not will finish it within a day or two.

I'm almost done but it's getting late so I'll finish tomorrow.

That is a great design. Thanks for sharing a build thread.

Wow! The concept you have is very simple and elegant! Thanks for the pictures. Now I have that miter saw Santa gave me for Christmas, I may have to try this out this week.
-Ken

Obviously the top and bottom boards have to be aligned at the 45º edge or the fins won't be square to the tube. Just how critical is the alignment and how much slop in the holes used to tighten the two together is acceptable?

I can't take credit for the design only the build thread and a few minor improvements to the original design. The boards do need to be lined up properly so use care when drilling down through the bottom board. My holes have very little slop. A 1/4" drill bit makes a tight hole for the 1/4" eye bolts.

Here is the last few pictures in the build process. The project wasn't difficult it only took me a couple of hours (and I'm slow). There are 4 critical issues to pay attention to:

1) The 2x6 needs to be dry, straight and flat so pulling an old scrap piece of 2x6 from the wood pile may not work.
2) The angle of the cuts is not critical but the cuts needs to be straight. If you are really, really good w/ a skill saw that might work otherwise a table saw is really needed to make the long angle cuts.
3) When using the top 1/4" holes to drill down through the bottom board make sure the 2 boards are aligned correctly.
4) The fin shims need to be the exact same thickness as the fins you are gluing in place.

Well that's it for now. My 3" build parts arrive on Tuesday so within a week or two I will post some pics of the Fin Jig in actual use.

My first use of the Fin Alignment Jig. 3" BT and 9 1/4"L fin.

The BT loaded in the cradle and the fin clamped in place waiting for the epoxy to set.

More pictures to come over the next few days.

Looks a whole lot like Qquakes jig. Is that where you got the idea? Thanks for doing a posting a how to thread.

bill2654 said:

Looks a whole lot like Qquakes jig. Is that where you got the idea? Thanks for doing a posting a how to thread.

Click to expand...

Yes I copied Qquakes jig and posted a pic in another thread. I was then asked to do a build thread. The jig was already built so I took a bunch of pics and added the dimensions and a few important notes. I really like the jig. The fin alignment looks spot on. It took the worry out of using the TLAR method.

Pictured is the 4th fin in the jig waiting for the epoxy to setup.

Another use is to put the rocket backwards in the cradle to hold it in the correct position for doing inside BT fillets. JB Weld along the MMT and TiteBond along the BT joint. Let the glue set and then give it a 1/4 turn ...... etc ...... etc ......

Outside BT fillets work the same way.