My quest for a perfect Fin Gluing Guide (FGG)

argylebill said:

Marc, you have done a great job in making the jig, kudos to you. Do you think a piece of peg-board would have worked out better while drilling the holes in the base-plate and in the wood plate attached to the aluminum? This question now has brought to my mind, the little there is left, but one could use the factory cut edges of the peg-board as guide line to draw for the laying out the different degrees of angle needed, 45, 90, 135, 180 and etc? right???

I do like your design and your comments while building the jig. It was a hoot in reading and picturing oneself in the same boat, but without AFLAC in the boat with you.
Bill

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Bill,

That's a really good idea, which didn't occur to me. So, excellent first post!

I'm also considering ideas that would give me continuously adustable mounting as well. I saved a second set of wood/parts to build a "Mark 2" version of this and may incorporate either the peg board or other ideas.

I've been meaning to update this thread for some time, but never got around to it.

The first jig (gluing guide) works great and I've built probably more than a dozen rockets of various sizes with it. However, there are two challenges in using it:

1. The upright guides need to be adjusted for each project to accomodate the specific positioning and thickness of fins. The guide is actually a bit cumbersome to adjust, particularly when going back and forth between 3- and 4-finned rockets. I wanted something that didn't require tools, and could be adjusted in a jiffy.

2. The adjustment process: I wanted a better visual guide for making sure the uprights are properly parallel to the centerlines of the fins normal to the body tube.

I experimented with all manner of different options, ranging from using drawer slides, U-channel materials, and all sorts of things. But I came back to a design similar to the original one, which gives very good positional adjustment capability and perfectly rigid uprights. Keep in mind, I was a little hampered by the fact that I don't have a complete woodshop with all the tools and skills needed.

Here's what I came up with:

It has the same kind of flat wood base I used on the version 1 guide, with the same side supports underneath the sides to prevent any warping.

I used a paper fin angle printout and extended the lines with a straightedge out to the edge of the wood base. The paper guide was sprayed with some spray adhesive (outside, that spray mount adhesive gets everywhere!) first, by the way.

I then carefully drilled a thin pilot hole right in the center of the fin lines, then used a 3/4 " bit that had a pilot spike, centering it carefully. Then I drilled the 3/4" hole all the way through.

This created a hole very close to 3/4" very close to the absolute center of the fin angles. Note, very close is not perfect, to the level of my OCD nature.

I then took a piece of all-thread bolt that I bought at Lowes or Menards and tried screwing it through the hole. I was able to do so, but the threads biting into the wood made the bolt cock a bit of an angle. I enlarged the hole slightly so the bolt just barely fit through freely.

The bolt, being 3/4", or about 19mm, was just a little bit too wide to fit inside a BT20 tube. However, enough of that width is out toward the edges of the threads, that I was able to sand down a bit of the metal using my bench mounted belt sander over most of its length (not the bottom two inches of it), so that a BT20 evenly fits over it, snuggly with NO slop whatsoever. It's a tight but not damaging fit. I simply passed the bolt back and forth over the sander with light passes rotating it all the while. It took about 20 minutes but was a perfect fit.

Note that another way to do this would have been to start with 5/8" threaded rod, build that up with say layers of paper, and slide a BT20 coupler over that, to serve as the mandrel for the fin jig.

The bottom two inches or so of the threaded rod were left unsanded, so they would thread properly onto the nuts that will attach it to the base. The rod was a little bit loose in the hole I made, so I took a short length of BT20, slit it so it could slide over the threads, wrapped with one layer of tape, and slid it through the hole. It was now snug in a good way, and without the threads biting into the wood, there was nothing to cause it to bias off perpendicular angle.

Two nuts and washers later, it was well-centered and fastened in place:

In the picture in the above post, you'll see some drill holes in the base... I had tried all manner of attachment mechanisms for the guides, with the drill holes being left over from the various attempts. All the ones you see above, I eventually cut around with a razor blade and made sure that the area was smooth so that the rough bumps you see wouldn't impact the final flatness of the surface.

Meanwhile, it was time to construct the uprights.

I wanted to make it so that they would be easily adjustable for different locations and fin thicknesses. After trying many things, I settled on hollowed out oak strips with thumbscrews sunk into T-nuts in the base, as the basis for holding the upright angle aluminum.

It started with a nice flat strip of half-inch thick by two inch wide oak from Lowes' craft area. I sorted through the bin of these pieces until I found the straightest one, which had no significant warpage in any dimension.



Using my router for the first time in about 7 years, I made four six-inch pieces with sections routed out in the middle. As you can see in the below picture, one of them is a reject due to the router grabbing the wood during the second pass. Oops. I eventually made another batch so that all told I had 4 good ones with a wide enough area routed out.



I also cut approximately 14" sections of angle aluminum (1"x1"x 1/16"). Also some lengths of 1/16" by 1/2" flat aluminum.

Here you can see a completed guide:



The angle aluminum is attached by two screws on the far side which you can't see, in holes through the aluminum a bit bigger than the screw shafts. This allowed me to adjust the angle of the angle to the base until it was perfect, then screw it in. Once screwed into perfect position as measured by a 90 degree angle (roofer's square or small L angle), I put a few drops of thick CA along the edges where the top surface of the oak meets the angle aluminum. Even the thick CA wicks in over time and made a great bond with the wood. I did this on a glass pane (it was a shelf from an Ikea cabinet at one time) while holding the upright at exactly 90 degrees to the glass. Between the screws and the CA it was easy.

The flat aluminum was also held on by thick CA. No big deal, though of course the process wound up with seeped CA that glued the uprights to the glass. It was delicate doing this but I got the hang of it.

Underneath, a bunch of T-nuts can be seen:



These allow me to put the uprights at various locations. For most projects, the two t-nuts closest to the center are used. With thumbscrews, it's easy to loosen the upright, slide it to where it needs to be for the fin thickness and location, then snug it down. Two thumbscrews with washers per upright is sufficient to lock the upright into place securely.

Here are some additonal pictures. Some show screws instead of thumbscrews; those pics were when I temporarily used regular screws before I got the thumbscrews.






The flat aluminum extensions allow me to visually judge the angle of the upright versus true to the fin guide line on the base over a long distance; this gives me accuracy probably to well under one degree.

You will notice the cut out sections of the oak give enough slop such that they can be adjusted over about a quarter inch space parallel to the fin center lines. This gives more than enough variablility to accommodate different fin thicknesses... theoretically up to half an inch thick fins.

Here's a few pics of my Solar Flare upscale getting fins glued on: