Making a turn fin

[Bob English]

This is something I have made for years. They are a fin and bracket for hydro's and Thunder boats. I have showed the process of making them on a different web site. I know some of the guys here go to that site and have seen them being made. But a lot of guys here have not. So is there any interest of seeing it done and the process explained?

 

[BrianNeumann]

I would be interested in learning a new skill, very nice turn fin!
Thanks for sharing,
Brian Neumann

 

[K F Wheeler]

I like the width at the bottom of the fin. Most people are making them narrower, there...
Easier to narrow one up than to make one grow!!
Ken

 

[Bob English]

I have had lot of guys over the years ask, just how do you make those fins? Well I will show it. I just got in a sheet of 7075 T-6 today and have some time to do some fins. First is to trace them out using the " Master fin template" Clamp the sheet to the work bench and get out the band saw and start cutting. I get them all rough cut first. I like to do 10 to 12 of them at a time. Anyone that has ever used a milling machine knows you just don't want to do items one at a time. If it took one hour to do one item it would take two hours to do four or five of them. Tomorrow I will get them stacked together and on the mill. I take more photos and show the next steps and explain what is going on.

 

[BrianNeumann]

Thanks for the info and details! How do you decide on a design, bend/type of bend, & dimensions for turn fin sizes on different hulls? Monos are obvious, but what about a 20 size rigger vs. a Sport 20 hydro? If I'm not mistaken, they use different shapes and bends? I know there are strict rules regarding Nitro 1/8 scale hydros so they look & handle just like full size hydros. Assume their turn fin is also the same design as a full size hydroplane as well? Im surrounded by many long time great rc boat racers in D-2 but I forget to ask them about details like this! Sorry if these are dumb questions, I only have experience with racing a JAE rigger so their fin is the only one I'm familiar with.
Brian Neumann

 

[K F Wheeler]

I do not know about what's allowed on scale boats in IMPBA... I just assumed a curved fin was legal on a scale boat! Hadn't even thought that a curved fin might not be legal! Just ordered material for a curved fin for a scale boat, yesterday. Figured the curved portion was below the water line so it was legal. Guess I should ask Joe W. since he's scale director for D2. I need to text him another question anyway... Joe just loves when I shoot questions his way! (NOT!!!) Because, I always have so many. Wow! It just warmed up one degree out here in Boonyville! It's 17 degrees At 6 am!! Sport 20 and 40 as well as a rigger myself.
Good questions Brian!!

 

[FloridaScaleBoater]

Curved fins are legal in both IMPBA & NAMBA
they DO NOT have to be true to scale.

 

[K F Wheeler]

Basically, Joe W. said whatever you want for a turn fin.
Ken

 

[Bob English]

Here are some more pics. I clamp all the cut pieces together with the master fin on top. Now drill the holes and bolt them together. Then into the vise on the mill. I use the master fin to guide all the cuts. It is the templet.

 

[Bob English]

You can see the end mill cutting the fins. After it is all done that big old stack of what looked like a mess in now a perfect machined stack of fins. Now unbolt them and peal off the outside layer of plastic film. Next step will be to mount them on the table I made and use a fly cutter to cut the taper into them.

 

[Bob English]

Got some more done on the fins. You can see the fin blanks mounted to the table in the vise. The table has a certain degree machined into it front to back and from side to side. A couple pics of the fly cutter cutting the taper into the fin. And you can see in the last photo the leading edge taper. So most of the angle is done by the mill and just the last sharpening is done on the belt sander.

 

[Hydro Junkie]

Bob, just a curiosity question on this one.
I've heard/read/been told that a square cut corner is a high stress area and a break waiting to happen. I see in your pictures that you actually cut a square corner with your fly cutter. Now comes my question:
Have you had any issues with fins bending or breaking at the corner where the taper is cut or considered running a groove or radius with a round tipped bit to remove the square corner? As I said, this is a curiosity question and nothing more

 

[Bob English]

Long story of how I ended up doing these fins, but it all started when the first Backlash kits came out. And I wanted a fin that runs better than the fin from Blazer. As I sold them to some other guys, they found out the same as I did. It runs better. Since then I have sold close to 700 of them and no one has ever told me they had one bend or crack. If you do them out of 6061 T-6 they will bend and not hold their shape. That is why I use 7075 T-6. 7075 is as hard as mild steel, but about one fourth the weight.

 

[Hydro Junkie]

The problem I heard about might have been from using 6061 but, then again, who knows. Could have been from using too thin of material as well. I might have to have you make me a set for some scale and gas scale boats I'm working on but that will probably be a month or two down the line

 

[shoboat]

Bob,

So how much does a 1/8th Scale turnfin cost shipped to 49685 in Traverse City,
MI ?

Thanks For The Information Bob,

Mark Sholund

 

[Roxyflash]

So where the fly cutter stops on the bottom do you cut it there again?

 

[Bob English]

These fins were done for gas hydro boats. If you 1/8 scale uses the same size as a gas boat you can run one of them. I get $65.00 for them. Or $87.00 for the fin and bracket set with hardware. And the pics of them you see on the screen do not do them any justice. The workmanship on them is very good. You see a lot of the mill work here, but later there is a lot of hand work and finishing done to them.

 

[Bob English]

Pics of the fins after all the fly cutter work is done. You might think Wow looks like it is almost done. NOT! Trust me this is not even half the steps I will go through doing them. Will work some more on them tomorrow.

 

[Bob English]

And now for the worst part of making the fins. Cleaning up the mess! Holly crap, a fly cutter has to be the messiest milling machine tool there is. That thing throws metal shavings ten feet in every direction. And I have to keep the mess cleaned up. The mill is in my garage. The last thing you want is to track metal shavings into the house and have your wife step on them barefoot! Not good.

 

[Bob English]

Did some more on the fins. Get them in the mill and cut the mounting slot so you can adjust the fin forward and back. Next step is to cut off the bottom of the fin. The lower hole was just there to be a mounting hole for the table and fly cutter. Now I go to the big disc sander and sand down the bottom of the fin. I want to make sure the top and bottom are square with each other. It just makes things go smoother later in the process if things are nice and square. Now I have the stack of fins ready for the next step on the big belt sander.