Fin Alignment Guide

[qquake2k]

Has anyone seen this? It looks interesting. I know there's no allowance for the thickness of the fin stock, and the fins would be slightly offset. But would that really matter that much? I supposed you could cut one of the angled pieces about 1/16" narrower. Has anybody tried anything like this?

http://gklandes.blogspot.com/2009/02...-straight.html

[Bravo52]

Seems to me that if you placed a shim between the two angled braces, it would allow you to get the right off-set. If you were using 1/8th fins, just put a 1/16 shim between and have at it........

What am I missing?

BTW, this is an amazing design. I'm mad becasue I didn't think of it......

[FatBoy]

I use this...

http://www.standardrockets.com/products.html

[clreynolds]

My geometry may be a little rusty, but since the tube is centered, a perpendicular line would be centered thru the vertex of the "V".
That means that half of the fin is above the line, and half below. So any shim should be the same thickness as the fin.

I must agree this is a very cool solution.

[bar-man]

I agree with clreynolds, a full thickness shim will do the trick and align the fins properly. I love the simplicity of the guide, assuming the two pieces are dowelled together for alignment and the whole thing held together with rubber bands it would be a really easy to use and accurate fin guide!

[chanstevens]

My geometry may be a little rusty, but since the tube is centered, a perpendicular line would be centered thru the vertex of the "V".
That means that half of the fin is above the line, and half below. So any shim should be the same thickness as the fin.

I must agree this is a very cool solution.

How would you be using the shim? If, for example, you put the shim between the fin and the open flat surface of the longer board, that would take the fin away from the center of the channel, making the problem of non-perpendicular worse. I'd think you would need to carve out a recess in the flat surface to lower the fin down by 1/2 the thickness of the fin for this to work. Either that, or you'd need a shim at the tip edge of the fin to raise it off the flat surface, and that would depend on the span length and fin thickness, not just the fin thickness.

That's the general problem I have with most every fin guide I've seen/tried--they do a great job of straight, not so great job of perpendicular, and are especially problematic when using an airfoiled fin.

[Viperfixr]

Add another vote for the SRAT--works very well.

I use this...

http://www.standardrockets.com/products.html

[Bravo52]

How would you be using the shim? If, for example, you put the shim between the fin and the open flat surface of the longer board, that would take the fin away from the center of the channel, making the problem of non-perpendicular worse. I'd think you would need to carve out a recess in the flat surface to lower the fin down by 1/2 the thickness of the fin for this to work. Either that, or you'd need a shim at the tip edge of the fin to raise it off the flat surface, and that would depend on the span length and fin thickness, not just the fin thickness.

That's the general problem I have with most every fin guide I've seen/tried--they do a great job of straight, not so great job of perpendicular, and are especially problematic when using an airfoiled fin.

No.....the shim goes between the two boards. The fin sits flat on the lower board......

This will work great.....now I'm going to my garage and steal this idea.

[qquake2k]

If you look very closely at this photo, you can see that the lower board is slightly wider than the upper board. I'm assuming this is how the builder dealt with the offset issue. Personally, I think the shim idea is better. You can use different shims for different thicknesses of fin stock.

http://picasaweb.google.com/gklandes...34500323588322

[clreynolds]

Good catch. That would have the same effect, but would be very hard to measure accurately. And if the two boards a glued together, it's only correct for one fin thickness only.

If the two boards are not glued, a shim looks to work best. In fact, the scrap left over from cutting out the fins would be the exact size. Recycling at it's best.

And I'm still impressed, and jealous that I didn't think of it first.

[Stymye]

nice fixture design but I still prefer something that aligns all fins in relation to eachother like the old estes fin alignment fixture.

[qquake2k]

nice fixture design but I still prefer something that aligns all fins in relation to eachother like the old estes fin alignment fixture.

I used to have two of the old Estes fin alignment fixtures, but have no idea what happened to them. I remember they worked pretty good, but did have some flaws. They used a series of "nested" motor blanks, with the 13mm blank fitting in a hole in the base of the fixture. The 18mm blank would slide onto the 13mm, and the 24mm would slide onto the 18mm. That was okay with 13mm or 18mm smaller rockets, but with bigger rockets, especially if the fins extended below the bottom of the body tube, it was difficult to get the rocket to stand up straight while you attached the three or four fins. Also, they could only accept two fin thicknesses, 1/8" and 3/32" I believe.

I don't know how well this homemade fixture would work for large (3" or 4") airframes, but I do like how it's not dependent on the motor mount. Plus, with different shims, you could use it with any fin thickness.

[MarkII]

My preferred fin alignment tool.

MarkII

[qquake2k]

My preferred fin alignment tool.

MarkII

Unfortunately, my old eyes aren't as accurate as they once were...

[Bravo52]

I've been thinking about how to use this on a larger airframe like a 3 or 4 inch tube. My thought is to take a piece of plexiglass and extend the edge to support a larger frame. The attachment points would have to be counter sunk in the wood, however, it should work. All of the "business end" is right at the junction of the two angled surfaces. Just extending the edges should make it work.

[qquake2k]

I've been thinking about how to use this on a larger airframe like a 3 or 4 inch tube. My thought is to take a piece of plexiglass and extend the edge to support a larger frame. The attachment points would have to be counter sunk in the wood, however, it should work. All of the "business end" is right at the junction of the two angled surfaces. Just extending the edges should make it work.

I'm not following you. The only thing I can think of is to use thicker material for the top and bottom, which would make the "vee" bigger.