LPR fin jig

[bjphoenix]

I've had ideas occasionally about building a fin jig. I have 5 builds starting so a good fin jig would be really helpful, but can I design and build a good one?

I've thought about it quite a bit. I was thinking about clamps, ways for things to slide, how to fit different tube sizes, and this was seeming to be pretty complicated. As I started working out the parts and how to build it I had ideas for how to make it simpler and eventually got it down to just a few pieces of wood. In the first picture you can see all of the parts, made from bits of scrap wood I had around.

In the last photo you can see how it works. I use rubber bands to hold the tube in the V blocks. I realized I could use gravity and not need any clamps, the fin just lays on the shelf and you slide it against the body tube. The glue is sticky enough to hold it in place. The shelf requires intricate adjustment to get the alignment right. I use cardboard and tape shims to adjust height of the shelf.

It's not quite perfect yet, I just put 4 fins on a Goblin. They don't align as well as I might be able to do by eye but the jig should be more consistent. After this first build I'll make another adjustment and see where it's at. For rockets with 3 fins it won't be as critical, with 4 fins the fins on opposite sides of the tube must align perfectly or you can easily see it.

The pieces of wood that have the V cut in them are about 2 1/8" wide, that's what the scraps of wood were, and this will fit up to a BT-80.

 

[cwbullet]

That should work. Nice design.

 

[kalsow]

I've had ideas occasionally about building a fin jig. I have 5 builds starting so a good fin jig would be really helpful, but can I design and build a good one?

If you're OK with putting on one fin at a time, here's another jig that's simple to make and use. They've worked well for me.

https://www.rocketryforum.com/threads/homemade-fin-alignment-guide.9694/post-80188https://www.rocketryforum.com/threads/homemade-fin-alignment-guide-version-2.9859/post-81989

 

[rharshberger]

I use a version of the ones @kalsow linked, easy peasy, and with 3d printed shims even easier.

 

[bjphoenix]

If you're OK with putting on one fin at a time, here's another jig that's simple to make and use. They've worked well for me.
https://www.rocketryforum.com/threads/homemade-fin-alignment-guide.9694/post-80188

I'm sure I've seen that one, and then forgot about it. It's simpler than the one that I did, and not as fiddly to get set. For that one you could change the shim between the 2 boards to adjust for different fin thicknesses. I was planning to only use 3/32" and 1/8" fin material so I didn't think adjustment would be needed, but actually that is yet to be seen. For the jig that I built, theoretically I would need to adjust the table by 0.015" to switch between 3/32" and 1/8", I was thinking I couldn't even see this much difference.

I'm used to the concept of one fin at a time, I've been in archery and fletched a lot of arrows one fletching at a time. A small jig could set close to my desk and I could take a quick work break periodically during the day to stick another fin on.

 

[bjphoenix]

If you're OK with putting on one fin at a time, here's another jig that's simple to make and use

I recognized the beauty of this design so I made one from some scraps. It is real easy to make if you have a table saw. I need to add some legs or feet under it next.

Here it is putting on its first fin on a BT55 rocket. (The fin shape should be a giveaway what this is.)

 

[kalsow]

I recognized the beauty of this design so I made one from some scraps. It is real easy to make if you have a table saw. I need to add some legs or feet under it next.

Here it is putting on its first fin on a BT55 rocket. (The fin shape should be a giveaway what this is.)

I can't tell from your photo, but remember to put scrap piece of fin stock between the two pieces of the jig so that the fin you're gluing is dead-center in the V-slot formed by the jig. I've screwed up a couple times...

 

[bjphoenix]

I can't tell from your photo, but remember to put scrap piece of fin stock between the two pieces of the jig so that the fin you're gluing is dead-center in the V-slot formed by the jig. I've screwed up a couple times...

I cut some scraps from the fin material that came with another kit and put in there. My actual fins are a bit thicker so I put in a couple of thin cardboard shims to get the same gap, you can see the pieces of cardboard sticking out the side of the jig. This might be the difference in material from one source to another, the fins on this rocket are cut from Hobby Lobby balsa, and papered with printer paper. The paper would add a tiny bit of thickness but it was obvious that the balsa core was thicker. I didn't tighten down on the screws a lot but maybe they compressed the balsa shims a little bit.

 

[Donnager]

When building smaller rockets (<3") I found having a few pieces of 1/8" thick channel, one 1"x2" and one .5"x1" can be used with a couple of shims (half the fin thickness) to clamp fins on a body centered on the tube, and in alignment. All the dimensions of the channels are half dimensions of the other direction, so it gives you a lot of flexibility, although it is only one fin at a time.

 

[Alan15578]

I have never had difficulty aligning and gluing fins one at a time, by hand and eye. The one fin guide that I made was to align all three fins at once to speed construction.

 

[bjphoenix]

I have never had difficulty aligning and gluing fins one at a time, by hand and eye. The one fin guide that I made was to align all three fins at once to speed construction.

I have been fairly good at it too, even models with 4 fins where you have to get the fins aligned on both sides of the body. 3 fins is much less tedious and demanding. However it takes more time and is somewhat tedious. I have to hold the fin in place until the glue grabs, then place the rocket down in a position where gravity won't do something bad to the alignment while it is drying.

The past few days I've been putting on a lot of fins using my copy of the other jig. It is quick and easy- put glue on the fin root, lay it on the jig, push it against the airframe, and leave it alone. Come back later and do the next one. And it also works very well for split fins. These go on straight and align well with each other.

This is my BT60 model inspired by the Wildman Darkstar.

 

[kenstarr]

These are gloriously simple fin jigs! Thank you! I recently made an overly complicated and difficult to use fin jig for a large rocket. It worked great but consumed a lot of time building it. For what it accomplished and what it cost, I did have fun and I suppose that makes it worth it.

 

[bjphoenix]

Here is an update- I've used the jig shown in post #6 for a number of builds and it is easy to use. I can put 2 or 3 fins on per hour. The largest body I've used it on was BT-60. That jig was crude because I made it from some scraps. I have builds I'm working on with BT-70 and BT-80 tubes and correspondingly bigger fins so I decided to take more time and build a new version of the jig. I finally got around to it today and it is ready to go. In the photo is a piece of BT-80 tube. Somebody may spot in the second photo that I haven't yet put in the spacer to hold the 2 pieces apart the same amount as the thickness of the fin material.

 

[mh9162013]

Here is an update- I've used the jig shown in post #6 for a number of builds and it is easy to use. I can put 2 or 3 fins on per hour. The largest body I've used it on was BT-60. That jig was crude because I made it from some scraps. I have builds I'm working on with BT-70 and BT-80 tubes and correspondingly bigger fins so I decided to take more time and build a new version of the jig. I finally got around to it today and it is ready to go. In the photo is a piece of BT-80 tube. Somebody may spot in the second photo that I haven't yet put in the spacer to hold the 2 pieces apart the same amount as the thickness of the fin material.View attachment 616419View attachment 616420

Thanks for sharing.

Was the rocket from Post #6 a BT-55 Citation Patriot? If so, how did it turn out?

 

[bjphoenix]

Was the rocket from Post #6 a BT-55 Citation Patriot? If so, how did it turn out?

I mentioned "clue" but the clue wasn't very good. The rocket is an upscale of the Centuri Javelin, upscaled from essentially BT-50 to Estes BT-55 size. The paint took a lot of work.
https://www.rocketryforum.com/threads/centuri-javelin-kc-31-or-5091-gallery.17582/#post-2429761

 

[mh9162013]

I mentioned "clue" but the clue wasn't very good. The rocket is an upscale of the Centuri Javelin, upscaled from essentially BT-50 to Estes BT-55 size. The paint took a lot of work.
https://www.rocketryforum.com/threads/centuri-javelin-kc-31-or-5091-gallery.17582/#post-2429761

Looks good!

And even though you didn't make a BT-55 Citation Patriot, I have realized that it might work with a Goblin nose cone.