Seriously Beveled Fins

[judo]

I'm now working on a =scale= BT-80 based Sandia Doorknob. I did a rough cut to shape today and I'll match sand tomorrow. I'd like to put a scale bevel on the fins. The bevel has been described as "Nike-style". The bevel will run from the trailing edge corner all the way to the root at a width of .811". Does anyone have any tips (and photos) of different ways to do that?

 

[judo]

3/32" basswood fins BTW

 

[DaveCombs]

Bench-mount a belt sander into a table vise and do work. That's how I did the leading edge bevels on my L1 rocket.

 

[Micromeister]

I'm now working on a =scale= BT-80 based Sandia Doorknob. I did a rough cut to shape today and I'll match sand tomorrow. I'd like to put a scale bevel on the fins. The bevel has been described as "Nike-style". The bevel will run from the trailing edge corner all the way to the root at a width of 1.147". Does anyone have any tips (and photos) of different ways to do that?

I've found what for me has provided the best nike type Beveled fins is to construct our model size fins the same way the real ones are made. out of folded sheet with a center or series of core ridges on double taper fins.
This is a Breeze on BT-80 size models using Sho-card (14ply cardboard) sheet styrene or better yet 3/64" lite-ply. All the pieces are CA and epoxied to gether making some incredibly strong, light weight fins. I've used is method on Nike Family models from BT-80 size down to minimum diameter Micro Maxx Nike smokes.

Trying to sand Accurate bevels with any of the various methods i've used frankly just doesn't give me the repeatablilty I'm looking for.
Hope this helps.

 

[Pem Tech]

I've found what for me has provided the best nike type Beveled fins is to construct our model size fins the same way the real ones are made. out of folded sheet with a center or series of core ridges on double taper fins.
This is a Breeze on BT-80 size models using Sho-card (14ply cardboard) sheet styrene or better yet 3/64" lite-ply. All the pieces are CA and epoxied to gether making some incredibly strong, light weight fins. I've used is method on Nike Family models from BT-80 size down to minimum diameter Micro Maxx Nike smokes.

Trying to sand Accurate bevels with any of the various methods i've used frankly just doesn't give me the repeatablilty I'm looking for.
Hope this helps.

Thanks John, this was a very helpful hint.
Could you give us a bit more detail on the process?

 

[powderburner]

I think Micromeister is pretty much on the mark with his suggestion.

The only way I found to get "repeatable" scale fin bevels by sanding solid finstock is to make some sort of tooling to carefully hold the fin stock in some particular position so I could work it back-n-forth on the sandpaper. Since this had to be done several times, and any tooling would scrub the sandpaper right along with the fin stock, the tooling itself had to be pretty durable. Otherwise the tooling itself would also sand away and change the angle/depth of the shaping on the finstock.

So, I bent some metal strap to make a box outline, carefully positioned and epoxied a piece of plywood inside the box, and used oversize pieces of finstock so I could tack glue the edges to the plywood to hold the finstock in position. And then the metal edges of the frame ate the grit off of the sandpaper. I went through a lot of sandpaper.

There has to be a better way.

For really nice, precision, scale fin bevels, you are probably going to go through some sort of similar monkey-motion, and a lot of it. Micromeister's approach looks like it would be as good as any, maybe better. (My only concern is repeatability of fin geometry, and that should improve with practice---also, you could make 10 fins and pick out the best four.)

Unfortunately, all of Micromeister's carefully prepared instructions and photos for fin construction are in the (currently lost) archives of TRF1. (Mods: hint, hint, nudge.)

 

[CharlaineC]

what about useing a angle and sanding a full sheet then after the tapers are the way you like cut out the fins

 

[judo]

Here is at what I'm looking:

 

[judo]

My one true blessing in all of this is I have a photocopier sitting about 10' away from me. I'm able to take the drawings and enlarge them to the exact size I need. By figuring, the leading edge bevel measures 2 degrees.

Micro,

Where could I find Sho-card (14ply cardboard) sheet styrene or better yet 3/64" lite-ply? Sheet styrene should not be all that hard; hobby shops are a-plenty around here. They're just not around the corner.

 

[Micromeister]

Thanks John, this was a very helpful hint.
Could you give us a bit more detail on the process?

Possibly:
I did a phantom Nike Apache using the same method to form up the multi piece Nike fins in clear frosted Polycarbonate. I seem to recall taking assembly photos during the Technique development. I'll see if I still have that build on another disc and post pics later if I do.

Basicly you'll layout the fin "skins" to the scale needed to double the layout then transferring it to the "skin" material. 1/64" 3-ply liteply is an excellent choice also. Cut the skin with the intent of using the folded connecting edge as the Leading edge for each fin.
Before doing any folding, score the interior of the material along the Fold ridge lines on both skins and it's joining LE. Use a steel staightedge or other sharp edged guide to crease the material along the ridge lines.
Most Nike fins taper in both directions as well as increaseing in thickness tip to root. A center support rib or ribs can be cut from the same material as the outer skins. Once we have the taper correct allowing for the thickness of the fin skin material, glue or epoxy the support rib(s) in place centered on the folded midspan crease.
Once the ribs are dry we can start working on folding the leading edge by scoring the inside and folding with that metal straightedge, working the straightedge back and forth to get the overall outer edge to about the proper thickness. We are doubling the material thickness at this leading edge, which may require some sanding on the outside to bring this edge to a proper knife edge. Before doing any sanding though REALLY Closely check the thickness of a full size vehicle fin edge, you might be surprised to fine they really are not knife edged to begin with ROTW is a great starting point for Scale Data but IT IS NOT completely accurate with regard to items like knife edge thicknesses. Check with other sources and if at all possible do some measuring yourself on the real thing.
Once your happy with the shape of your forward edge; Match up the rear edges were the skins match up with themselves and the standing rib(s). There will almost always need to be some adjustments, and each fin will end up with some small varience (as to the full size fins I might add).
Once you have a good fit run CA or epoxy along the inside standing rib(s) and one rear mating edge. Attach and tape the tailing edge and sit the fin on a table of other surface to check that the rib is matching up in the fold of the opposing skin fold. Weight the assembly and let dry.

Judo's Doorknob fins will have an end plate to install as well to make up the root edge fillers. He can have a couple ways to do this. Create another full thickness "rid" to serve as the end plate filler or.
Find a convenient thickness materal to act as a "core" for his fins allowing his skins to be a thinner material yet. forming very nice tight bevels along the leading edges.
Hope that makes sense Judo.

 

[Micromeister]

My one true blessing in all of this is I have a photocopier sitting about 10' away from me. I'm able to take the drawings and enlarge them to the exact size I need. By figuring, the leading edge bevel measures 2 degrees.

Micro,

Where could I find Sho-card (14ply cardboard) sheet styrene or better yet 3/64" lite-ply? Sheet styrene should not be all that hard; hobby shops are a-plenty around here. They're just not around the corner.

Judo:
Remember to try to match the scale thickness of the prototype with whatever you decide to use as the "skin" material. Believe me once these fins are assembled they are very strong.
Most Nike fins are 1/8" alum sheet. if the Doorknob follows suit you could be able to use any number of skin materials.
Sheet styrene can be had from all kinds of sources, Plastistruct and Evergreen brands from most any Hobby and/or Craft or art supply stores, it's also easily obtained from industrial supplies like McMaster-Carr.
1/64" and 3/64" 3ply Lite-ply birch plywood are a local hobby shop thing
Sho-Card, Illistrator board, Railroad board and other materials like foamcore can be had from most any Art supply, Sign supply house or on-line. Don't poo-poo plain old cardstock either, after a couple coats of thin CA you've created a Phenolic laminate (Plastic impregnated Cardboard) of sorts
I used foamcore under 3/64" ply to form the one piece main fins on my upscale BT-101 Laser-X. While not turely tapered in the same way it could have been.
Hope this helps.

 

[MarkII]

John's (Micromeister's) method is an excellent way to do it, and is often the only way to get them done with precision. But I have also done them another way - by building up the shape with stacked layers of material that are laminated together, and then molding/carving the sharp bevel out of Bondo that is "bonded" to the edge. This results in a solid core fin, which may be more desirable, depending upon the size, shape and thickness of the fin. But don't misread what I am saying here - I think that the hollow core built-up fin construction method is overall the best way to go in the vast majority of situations. It can give you precise control over the dimensions, which is so important in scale or sport-scale builds. I'm mentioning my other method as more or less just a side note. There are specific reasons why I am using it in one build that I am working on now - reasons that may not apply to too many other situations.

MarkII

 

[Micromeister]

Yep! Marks method is good also. laminated layers is a great way and gives builtin guide lines for shaping.

Found the Phantom Nike Apache build photos.
The fins are double tapered as well as tapered tip to root. This ment I altered the construction a bit using to Tip thickness as the Fold starting point. Unfortunately it gonna take 3 posts to add all 15 photos.
Hope this helps with your normal materials build. The procedure is about the same for single taper and blocky type fins, though I'd use the leading edge as the fold point as it makes for a stronger fin.
We can build fins out of matching pairs of outer skins it just takes a little more time in alignment making sure both halfs match up properly. It also generally requires a little Bevel sanding of the skin's mating edges to help close the gaps, reduce the thickness and hide the seams.
I'll just load the photos, if there are questions I'll try to answer, but I may be a little scarce the next couple days. I've got some excellent weather coming tomorrow and Sunday.... Have some micro test flying to do

Hope this Helps.

 

[Micromeister]

next 5 fin making pics

 

[Micromeister]

Last 5 fin making pics

 

[judo]

Yes, this is making sense to me after a couple of read-throughs. The clear Nike fins are very helpful. I'm using VCP to print the fin plan forms. I'm also planning on TTW fin tabs as this one is going to be a 4x24m cluster. I'll have to sit down and figure out how to place the internal braces. Hey, if I weren't learning something, what would be the point?

I don't think that there is a way to reverse the fin plans on VCP. I'll probably print two and flip one and tape them together at the leading edge. That will give me the cut-out for the hollow fins as well as give me an idea of how much material I'm going to need.

ROTW is a great starting point for Scale Data but IT IS NOT completely accurate with regard to items like knife edge thicknesses. Check with other sources and if at all possible do some measuring yourself on the real thing.

Data on the Doorknob is scant on the internet. ROTW may be my only source. Sandia used the Doorknob only between 1957 and 1959 (Same time span as the Ford Edsel, I think). LOC makes a 7.5" version and when I first saw it I thought it was an odd name for a rocket. I wondered why anyone would name a rocket by that name. Barry, are you out there? Have you got any data I could use?

 

[judo]

What about skinning some sheet styrene over some 1/16" basswood? The sheet would be cut and folded as described but then placed over a triangular section of the 1/16" basswood. The only thing left to cover would be the tip edge.

 

[Gus]

Judo,

Try one first out of simple cardstock. I think you'll be really surprised at how strong these are.

I just built one of Sandman's Roachwerks Pershings, which used this technique for the fins. The fins are amazingly strong. For a BT-80 sized model there is probably no need to go with something more expensive than 65 or 110 lb. cardstock.

 

[georgegassaway]

What about skinning some sheet styrene over some 1/16" basswood? The sheet would be cut and folded as described but then placed over a triangular section of the 1/16" basswood. The only thing left to cover would be the tip edge.

That is how I have done "Redstone Missile" type fins, for Mercury Redstone and Juno-I (Explorer-1) models. A balsa core where it is thick, and thin plastic sheet "bent" sharply at the break line. In my case, I use two sheets of plastic, and use Scotch tape to temporarily hold the leading edges together. I CAREFULLY run some thick CA (never thin CA) inside of the leading edge joint to bond the two touching plastic sheet edges together. Then after they cure, I peel off the Scotch tape.

- George Gassaway

 

[MarkII]

For my Apollo 7 Celebration Saturn 1B, I copied the cardstock fin covers onto 0.010" sheet styrene, and used these styrene covers instead. The reason was because after I built one fin with the cardstock, I noticed that the covers buckled, or "puckered" over the ribs, allowing their outlines to show through. (Kind of like a skinny man whose ribs are showing through his skin.) I'm sure that I could have fixed that with a little CA and Fill 'N Finish, but I was pressed for time.

I followed the recommended method for this material, and scored the leading edge line beween the two halves, so that the styrene would break there and fold over the ribs on either side, and then covered the scored line with a strip of 1/2" wide Mylar tape on the inside of the skin before breaking it at the score line. The rest of the assembly went fine and I got nice smooth-sided fins with no visible rib outlines. But later, when I went to bond the fins to the model, I noticed that the two halves of the skins on some of the fins were spreading apart at the break. It appeared that the Mylar tape wasn't quite strong enough to hold the two halves together at the leading edge. I hastily applied some Squadron Green putty to the leading edges in order to fill in the gap created by the two halves spreading apart, but by then I was REALLY pressed for time, so I didn't do as thorough of a job as I would have liked.

Fortunately, after the original separation (which wasn't really all that bad - it was unexpected, though), the spread didn't get any worse. I think that it may have been caused by my use of a slightly thicker material for the skins than the model was designed for, while keeping the height of the ribs, and the size of the skins unchanged. I could have used 0.005" sheet styrene (I had some) instead, but I was afraid that material that thin would allow the outline of the ribs to show through, just like the cardstock had done.

A couple of things that I could have done to prevent or at least minimize this problem (had I known that it could happen) would be to give the sides of each rib a couple of licks with some medium-grit sandpaper to very slightly reduce their height. This would help them accommodate the slightly thicker material. The other thing would have been to apply a very small bead of 30-minute epoxy to the leading edge at the break immediately after building the fin, smoothing it down with a nitrile-gloved finger that had been slightly dampened with denatured alcohol, and then clamping the edge until the epoxy cured. The spreading at the leading edge didn't happen right away; I was bonding the fins to the model about a day after I had assembled them, and it was only then that I noticed it. So if I had known that it would happen, I could have taken steps to mitigate it right after I had built the fins.

BTW, I was introduced to the hollow core built-up method of creating fins when I was putting together my Estes Industries K-30 Little Joe II back in 1970. I have to admit that when I read the part of the instructions that covered the assembly of the fins, and saw what I had to work with, my first impression was "Man, that's cheap!" (not in a good way). But by the time I had finished them, I was totally won over. The fins were great! I could not imagine what would have been involved if the plans had called for me to sand them into their final shape. I had very rudimentary model building skills and practically no tools back then. And Micromeister is right - I learned from later research that this was exactly how the fins on the real Little Joe II's were built.

MarkII

 

[judo]

Gus, are you suggesting cardstock over a balsa/bass base or straight cardstock? I'm working this weekend and broke until payday so I will be making zero progress any time soon. I can get card stock at office supply stores, right?

 

[sandman]

I've seen Norm Abrahms on "The New Yankee Workshop" use this tool for cutting tenons and wondered if it could be used to cut the fin bevels on a table saw.

It would only work on larger fins like 1/4" or thicker. If it would work.

https://www.woodcraft.com/product.aspx?ProductID=144755&FamilyID=4847

I don't do enough mortice and tennon joinery to justify the expense.

 

[rocketguy101]

Gus, are you suggesting cardstock over a balsa/bass base or straight cardstock? I'm working this weekend and broke until payday so I will be making zero progress any time soon. I can get card stock at office supply stores, right?

I used 110# cardstock over balsa ribs for an "F" powered semi-scale Terrier-Sandhawk. After assembling the fins as outlined in the posts above, I coated the card w/ CA (do this outdoors or in a well-ventilated area!!). When dry, they are like plastic. The model flew great with no signs of damage after landing on hard Oklahoma ground.

As mentioned above, I first ran into it w/ the Estes LJ II, and the then a CMR D-Region Thomahawk. It is a fantastic method to make these types of fins.

 

[powderburner]

I can get card stock at office supply stores, right?

Yes, most should carry it. If I am looking for big sheets (8 & 1/2 x 11), I get mine at Wmart. A ream of this stuff is only a few bucks and lasts a long time.

If you are just "learning" or messing around, don't forget you can do a lot of building with a package of 5 x 8 notecards. A lot of times, you can find these at dollar stores.

 

[MarkII]

Yes, most should carry it. If I am looking for big sheets (8 & 1/2 x 11), I get mine at Wmart. A ream of this stuff is only a few bucks and lasts a long time.

If you are just "learning" or messing around, don't forget you can do a lot of building with a package of 5 x 8 notecards. A lot of times, you can find these at dollar stores.

Georgia-Pacific White 110 lb. Cardstock, 8.5" by 11", pack of 150 sheets, $5.29 at the Walmarts in my area. Good stuff.

I print out all of my fin templates on it when I am cloning rockets from old plans. Also useful for making shrouds and paper transitions for LPR builds (like the tailcone on the Midget. I create the shroud patterns in VCP.)

When I first got back to building rockets a few years ago, I went through a few packs of the stuff while I was building every free paper rocket that I could find in the web - and then upscaling and downscaling them. In the attached pics are my Mega Midnight Express and two Micromaxx Midnight Expresses (design and patterns from FlisKits.) The Mega ME's body tube, body tube couplers and the nose cone shoulder are all constructed of multiple layers of cardstock, and I used a length of 2" Schedule 40 PVC pipe as a mandrel for making the tube. The nose cone is made from a single layer of posterboard that I fiberglassed (crudely) on the inside surface. The fins, which are hollow on the regular ME, are solid basswood, with the skins epoxied on, and they are mounted TTW. It has a 38mm motor mount; the motor tube was also constructed out of cardstock. The entire rocket is obscenely overbuilt, though. It stands 41" tall and, with recovery system and nose weight, it tips the scales at a portly 52 oz. (JUST under the weight limit for a required FAA waiver. The nose weight is adjustable, though, and it may not require quite as much as I have in it.) I built it to fly on F and G motors, but because it was so hefty, it really needed an H when I completed it. Since I don't have high power certification, I have never flown it. (Since then, Aerotech has come out with the G79W, the G76G, and the new version G80T, all of which I can buy without certification. They are all powerful enough to get this pig safely up into the sky, but I haven't had a chance to try them yet.) I built it in 2005, when I was still a newly-minted BAR, and barely knew anything. I wanted to build a BIG paper rocket, which is why I used cardstock or posterboard wherever I could. The solid basswood fins were a mistake, and I will never try building fins that way again. It was an interesting project, though, and I learned a bit about various materials and adhesives.

The two Micromaxx downscales were built in the conventional way, and are 4.094" tall by 6.9mm in diameter. Each one has a single copper BB CA'd into the nose cone for nose weight. A third micro version was flown once and went totally out of sight, never to be found.

MarkII

 

[FROB]

If i were doing this,
I'd probably cut them out of a Styrofoam block (cut to the semi-span thickness from a plank of insulation) - using a hot wire "cheese" cutter (easy to make from a discarded hair dryer/toaster etc) with some tip and root templates pinned to both sides. Its easy, quick, and clean.
Then I'd laminate some skins on with thin epoxy- i have some 0.06" thick G10 (paper thin) thats great for this sort of thing, otherwise card stock or 1/64 balsa would work well too.

By the way i found 110 lb card stock in a pack of 500 8-1/2"x 11" sheets at staples for < $10, thats basically a lifetime supply. If you have a printer with a sheet feeder & straight-through paper path option (most do) it works great to just print your fin, tube, centering ring and transition patterns directly on it.

 

[MarkII]

If i were doing this,
I'd probably cut them out of a Styrofoam block (cut to the semi-span thickness from a plank of insulation) ...

I have heard of this technique. Where can someone obtain the styrene foam?

By the way i found 110 lb card stock in a pack of 500 8-1/2"x 11" sheets at staples for < $10, thats basically a lifetime supply. If you have a printer with a sheet feeder & straight-through paper path option (most do) it works great to just print your fin, tube, centering ring and transition patterns directly on it.

That's a really great price! Thanks for the tip! In my case, a 500-sheet pack would last me about a year, maybe two. I put the 110 lb. right in my regular paper tray, and it goes through the normal 180° paper path in my HP Deskjet just fine. Even the automatic duplexer has had no problem with it, on the few occasions when I have run the cardstock through it. I have been doing that for 5 years now with the same printer. I do use the straight path to print on heavyweight poster board, though. My printer doesn't have a tray for the straight path, so I just feed the sheet in by hand. I just wish I could afford to buy a wide-format printer, just so that I could print very large templates and plans!

MarkII

 

[FROB]

I have heard of this technique. Where can someone obtain the styrene foam?

Any construction supply store- home depot etc 2' x8' planks up to 3" thick
don't get the expanded bead type, the homogeneous kind is much better for this.

 

[judo]

Rocketguy101,

Beautiful! How did you make those ribs???

As of right now I'm thinking of going card stock over balsa. I'll have to spec out the total overall thinkness. I've got a little 1/16" balsa and gobs of 3x5 cards. Maybe I'll do some playing Monday. I've been running hard doing the x-ray thing today for 13 hours now and I'm beat!

 

[Gus]

Gus, are you suggesting cardstock over a balsa/bass base or straight cardstock? I'm working this weekend and broke until payday so I will be making zero progress any time soon. I can get card stock at office supply stores, right?

Judo,

Yes, cardstock over balsa. I bought both 65lb and 110lb cardstock at an office supply store 3 years ago and I still have lots left, LOL. But if you want to practice before payday just use some spare balsa strips and cardboard from 3 x 5 cards. You'll be very surprised at how quickly you get good at building them and how strong they are.