tomach fin shaping

I finally opened up my Tomach box. The parts all look great! Madcow kits are excellent quality.

The fins are a little thick and square. Are other people beveling or rounding their fins? My other thought is that the rocket is going so high as it is, square may be fine!

Which version (size) do you have?

I have the 1.6" size with the1/16" fins, but I plan on trying to bevel them anyway

Sorry, I have the minimum diameter 54mm one. I keep forgetting there are others, even though the others look nice too.

watermelonman said:

Sorry, I have the minimum diameter 54mm one. I keep forgetting there are others, even though the others look nice too.

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glass or CF? I have the CF 54mm MD and the fins came air-foiled. I don't know if the glass kits do, but there are at least two 54mm MD glass build threads on the forum.

Edit, I just found AlnessW's build thread and from this pic the glass fins are not air-foiled.

It's about time you started working on this Eric! Lol. On mine I did a bevel that extended about 3/4" back from the edge. I just did it by eye with a belt sander in a vice. Now that I am finishing up the tip to tip, I am sanding the final bevels, and now they are sharp enough to cut you, which my finger found out while sanding. If you aren't going for ultimate performance, rounding them should be fine.

I find beveling to be a pain. I don't particularly enjoy it and every time I start a build I tell myself that I'm not going to bevel the fins. Eventually I sit down and bevel them, and they always look so much better with the bevel than without. I don't think I'd ever leave the fins square, but to each their own. For beveling, I like to use a sanding band on my dremel tool. I clamp it into my work bench at an angle, then I lay the fin flat on a board and run it back and forth across the sanding band. It doesn't take a lot off on each pass, so it takes a little while, but the results are pretty consistent.

Has anyone done the leg work/math to see what kind of drag reduction is achieved by beveling or airfoiling the fins? So many military rockets/missiles don't bother that I wonder what kind of gains it's actually producing (other than aesthetic). May not be a great comparison because they are mass produced to a price, but who knows.

I shaped mine... only to make them look cool.

rc dude said:

It's about time you started working on this Eric! Lol. On mine I did a bevel that extended about 3/4" back from the edge. I just did it by eye with a belt sander in a vice. Now that I am finishing up the tip to tip, I am sanding the final bevels, and now they are sharp enough to cut you, which my finger found out while sanding. If you aren't going for ultimate performance, rounding them should be fine.

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Definitely not ultimate, as this one will be durable and intended for many flights over the years. I would like to do a fully optimized minimum diameter record hunter some day, but too many compromises on this build.

DizWolf said:

I shaped mine... only to make them look cool.

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Those look great! I suppose I need to do something to the fins, then.

So, they are all root glued. How should I order the bevel vs tip to tip? Normally I would have done that first, but too late now!

I usually at least round the edges on my fins just to aid in finish durability. Paint on a rounded edge will be more durable, and, not chip as easily as it will on a sharp edge.

mpitfield said:

Edit, I just found AlnessW's build thread and from this pic the glass fins are not air-foiled.

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Say, where'd you find that photo?

I beveled mine using an orbital sander after finishing the tip-to-tip. Worked great:


See https://wilsonalness.com/rocketry/projects/tomach.html for the full project, if you haven't already. Fun build! Hit 14,929' on one of my motors at Black Rock last year.

rc dude said:

It's about time you started working on this Eric! Lol. On mine I did a bevel that extended about 3/4" back from the edge. I just did it by eye with a belt sander in a vice. Now that I am finishing up the tip to tip, I am sanding the final bevels, and now they are sharp enough to cut you, which my finger found out while sanding. If you aren't going for ultimate performance, rounding them should be fine.

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Hey Kyle - you finally going for that L2?

AlnessW said:

Hey Kyle - you finally going for that L2?

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I will be this June! Going for it at either LDRS or Mudrock, currently leaning towards Mudrock. Already received my L935 from Wildman's black Saturday sale.

rc dude said:

I will be this June! Going for it at either LDRS or Mudrock, currently leaning towards Mudrock. Already received my L935 from Wildman's black Saturday sale.

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Sweet, you're flying the L935 for the cert? I won't be at Mudrock, but am still thinking about LDRS...TBD...