Beveling Fins
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mkadams001
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I would do it exactly as the instructions describe. Do the layout lines and sand with a block. If you need to, practice on some scrap balsa to get the feel of the angle that you need to hold the block and how fast the balsa is cut by the sandpaper.
bradycros
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Construct a mechanical device that is self adjusting as material is removed.
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The main thing is not to go to fast. You want to use coarse sandpaper since the balsa will clog up fine sandpaper so don't use too much pressure and check your progress frequently.
Kruegon
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This will be an interesting (and possibly expensive and time consuming) endeavor. But it's a skill I need to perfect. I'd like to be able to bevel the fins on my mini Honest John the same way. I may cut extras of it and practice there first. Cheaper fins lol.
Incongruent
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Probably too late to help on your build, but...
As suggested, draw, with pencil, the guide lines, but also add strips of making tape (the normal stuff works) to the two edges on the fin surface and on one side of the bevel (slightly over the line). Burnish the tape down, then sand down the area between the masking tape. Remove the tape on the leading edge and put a new piece on the newly sanded surface, overlapping the pencil line you drew. Sand down carefully, since the balsa is getting thin. I've laid the fin with the bevel sanded first flat on the table, sanding over the edge of the table on fins with a uniform bevel. This probably would't work on a tapering bevel (wrong terminology, probably). After you have the bevel (with a small flat leading edge), use a q- tip to Medium CA the flat surface and a little bit over. After it dries, sharpie that flat, CA covered surface. Sand down on both sides until the leading edge is suitably thin, inspect, and if satisfactory, sand off the sharpie (the CA stopped it from soaking into the balsa AND strengthened the balsa while sanding. I would paper the fins and CA the leading edge so it can be further sanded into a knife edge and for strength. It helps to have the paper creased into a bevel and the fin inserted into it, so for kits that have the leading and trailing edge beveled (not sure about Phoenix), two layers of paper might be needed, with one ending at the edge of a bevel (or both, and CA in the gap, then sanded.
The masking tape should be removed before CA ing the fin or papering. After the beveling it isn't needed.
You can also just CA and sharpie the leading edge and use a sanding jig (but masking tape helps on the surfaces.)
Well, hand sanding on long bevels works too, just not as neatly. You actually have to pay attention to the build.
Just my experience, which is certainly not enough.
-Tony
As suggested, draw, with pencil, the guide lines, but also add strips of making tape (the normal stuff works) to the two edges on the fin surface and on one side of the bevel (slightly over the line). Burnish the tape down, then sand down the area between the masking tape. Remove the tape on the leading edge and put a new piece on the newly sanded surface, overlapping the pencil line you drew. Sand down carefully, since the balsa is getting thin. I've laid the fin with the bevel sanded first flat on the table, sanding over the edge of the table on fins with a uniform bevel. This probably would't work on a tapering bevel (wrong terminology, probably). After you have the bevel (with a small flat leading edge), use a q- tip to Medium CA the flat surface and a little bit over. After it dries, sharpie that flat, CA covered surface. Sand down on both sides until the leading edge is suitably thin, inspect, and if satisfactory, sand off the sharpie (the CA stopped it from soaking into the balsa AND strengthened the balsa while sanding. I would paper the fins and CA the leading edge so it can be further sanded into a knife edge and for strength. It helps to have the paper creased into a bevel and the fin inserted into it, so for kits that have the leading and trailing edge beveled (not sure about Phoenix), two layers of paper might be needed, with one ending at the edge of a bevel (or both, and CA in the gap, then sanded.
The masking tape should be removed before CA ing the fin or papering. After the beveling it isn't needed.
You can also just CA and sharpie the leading edge and use a sanding jig (but masking tape helps on the surfaces.)
Well, hand sanding on long bevels works too, just not as neatly. You actually have to pay attention to the build.
Just my experience, which is certainly not enough.
-Tony
TopRamen
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Get machines. They have miter gauges that are made to bevel things.
They cost less than most rocket kits, you just have to clean them up and have a space for them to operate.
You can probably get by with just a few motors too, and swap them between the machines, or if you have ceiling or floor space, set up an old school one motor for all belts system. the run them inline or use flat belts to go around corners.
It might sound hokey, but having gotten into that kind of stuff, I have seen examples that can out perform today's modern equipment when it comes to the measurable tolerances in the bearing surfaces, so you can take it or leave it.
I recently unearthed a top section of a Babbitt Bearing in my yard, and wish that I had a Babbitt bearing Machine to work on, but that will come too when the time is right. My top casting with Babbitt in it is likely just from an axle of a Model something or other vehicle or cart.
They cost less than most rocket kits, you just have to clean them up and have a space for them to operate.
You can probably get by with just a few motors too, and swap them between the machines, or if you have ceiling or floor space, set up an old school one motor for all belts system. the run them inline or use flat belts to go around corners.
It might sound hokey, but having gotten into that kind of stuff, I have seen examples that can out perform today's modern equipment when it comes to the measurable tolerances in the bearing surfaces, so you can take it or leave it.
I recently unearthed a top section of a Babbitt Bearing in my yard, and wish that I had a Babbitt bearing Machine to work on, but that will come too when the time is right. My top casting with Babbitt in it is likely just from an axle of a Model something or other vehicle or cart.
Incongruent
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Get machines. They have miter gauges that are made to bevel things.
They cost less than most rocket kits, you just have to clean them up and have a space for them to operate.
You can probably get by with just a few motors too, and swap them between the machines, or if you have ceiling or floor space, set up an old school one motor for all belts system. the run them inline or use flat belts to go around corners.
It might sound hokey, but having gotten into that kind of stuff, I have seen examples that can out perform today's modern equipment when it comes to the measurable tolerances in the bearing surfaces, so you can take it or leave it.
I recently unearthed a top section of a Babbitt Bearing in my yard, and wish that I had a Babbitt bearing Machine to work on, but that will come too when the time is right. My top casting with Babbitt in it is likely just from an axle of a Model something or other vehicle or cart.
But "I beveled them with a machine" doesn't come with bragging rights...
I agree, it would be easier (and possibly more accurate) with a jig or machine. But it's less fun... well, er... tiring...
TopRamen
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Yes, very true indeed.
I found myself in a bad way at the drill press today, and will now have to build a foot pedal for the control of it.
Even the machines are not a magic fix for Arthritis and nerve problems, yet we have to go on and build no matter what the heck is going on around us, so build we will.
There's somw CNC stuff that's got my attention, but it is not very accurate so I'm not to interested. the cool thing is that it operates on it's own, and I could always build actual measured guide rails for it.
We'll see what happens.
Modern laser machine produced stuff cannot reproduce the old Arn it was made on by machinists in the 30's, so I'll never have faith in a modern tool unless it is like those from the Northfield Shop.
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Ditto Tony:
I'll add only one addtional suggestion: If you intend to use Balsa for these large fins and straks you should leave at least 1/32" at the leading edge after sanding this will give a little area that will avoid snapping off feathered leading edges as you prime and paint. Not to mention it will help maintain those edges on landings.
A good sanding block or T-bar is essential to achieving good even edges.
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Incongruent
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For really big balsa fins, there was a person sandwiching a layer of fiberglass with two sheets of balsa. They said it beveled well. I haven't done anything big enough for that method, but it seems like it'll work.
As for leaving the 1/32 inch, bare balsa of below that thickness is fragile, (ask me how I know that) yes, but papering the fins reinforces against the grain and CA wicking the leading edge makes it feel like a plastic knife in hardness. (And less brittle) I wouldn't be worried about the fins breaking during construction. As for landings, it'll dent either way, just not as much with thicker balsa. Luckily, most scale models with beveled trailing edges have rectangular or trapezoidal fins, so it's at least possible to land on the tube.
As for good, even edges, yes, a flat sanding surface like a sanding block is crucial, but masking tape makes it much easier and even as well.
As for leaving the 1/32 inch, bare balsa of below that thickness is fragile, (ask me how I know that) yes, but papering the fins reinforces against the grain and CA wicking the leading edge makes it feel like a plastic knife in hardness. (And less brittle) I wouldn't be worried about the fins breaking during construction. As for landings, it'll dent either way, just not as much with thicker balsa. Luckily, most scale models with beveled trailing edges have rectangular or trapezoidal fins, so it's at least possible to land on the tube.
As for good, even edges, yes, a flat sanding surface like a sanding block is crucial, but masking tape makes it much easier and even as well.
Kruegon
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Not too late at all. I generally start studying methods months in advance of implementing them.
A basic single bevel doesn't scare me. The edging on an Estes Phoenix is a single bevel on the long edge and a single bevel on the tip.
The bevel on a Smoke and HoJo are mite red bevels. It's beveled from front to back but also thickness beveled from root to tip.
I've explored a method for the HoJo where leading edge is beveled over the center line. Then the trailing edge bevels back to the line. Mathematically, this should automatically create the thickness feather from root to tip. And repeat for the other side.
The smoke creates a different issue. The same method can be applied to the bevels, but the root to tip feather must be done separately. And it's such a tiny angle to work with.
I think I need to find a better sanding block as well. I saw one somewhere that appeared to be aluminum a with a contoured handle. This appeared to be a decent option. Now I just need to locate a source for it.
If you mean the Great Planes sanding block (and I'm guessing you do) they're available from Amazon and most hobby shops. I have one and like it a lot. They come in assorted different lengths.
Incongruent
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I would taper the fin, then use masking tape in the flat surface and either CA+Sharpie or masking tape on the leading edge. Another person did the unbeveled parts in plywood and the the beveld regions in balsa, then sanded it down. The two tapered pieces on either side of the bigger center ply were tapered, then the balsa was glued on and sanded down. Same concept as the tape, where the places needing a bevel sand easier.
I would agree that that a good sanding block helps, but I got good (in my opinion) bevels with some sandpaper glued to a Home Depot Paint Stir Stick. It should be mentioned that the stick was sanded to a 1000 grit, though. (Yay Redundancy!)
Just be careful and don't sand too forcefully off the edge, especially the tips. Luckily, paper covers up the seam where the tip gets glued back on well.
Another way could be to bevel the fins evenly and then sand the taper in by masking from where the bevel ends on the root edge to somewhere on the outer edge. Masking tape is laid outwards towards the closest edge. (I'm not sure if this was what you were describing.
-Tony
It's amazing how most things I do in a build that I come up with myself are originally for someone else.
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