Questions on beveling a Plywood fin

[Endymion42]

I'm building my first rocket (NCR Hyperswift) with plywood fins and have a couple questions about proper beveling of plywood. Note that I don't plan to laminate the beveled fin with anything, just using the plywood and sanding sealer.

1) The plywood is 1/8" with outer layers 1/32" in thick and a 1/16" inner dark layer. Should I avoid digging into the dark layer when beveling (seems this would not allow for much beveling at all)? If I dig into the dark layer am I compromising the strength of the plywood significantly?

2) What angle to bevel at? Long 10degree taper or just round the edge a little?

I'd appreciate any thoughts on this.

Thanks,
John

 

[waltr]

I leave a bit of un-beveled edge on plywood fins. Maybe about 1/32 to 1/16.
It is typical that the plywood core can be rougher or softer than the skins. If so then wick into the core (leading edge) some thin CA or other sealer.
The edge can be left 'squarish' or rounded, that's up to you. I always put some taper on fin leading edges only for looks not for performance but it does help reduce drag.

 

[Endymion42]

Thanks Walt.

 

[majordude]

I leave a bit of un-beveled edge on plywood fins. Maybe about 1/32 to 1/16.
It is typical that the plywood core can be rougher or softer than the skins. If so then wick into the core (leading edge) some thin CA or other sealer.
The edge can be left 'squarish' or rounded, that's up to you. I always put some taper on fin leading edges only for looks not for performance but it does help reduce drag.

I only did it once but you can get wooden dowels and glue it to the leading edge and fill in the gap with your favorite filler.

 

[lakeroadster]

I'm building my first rocket (NCR Hyperswift) with plywood fins and have a couple questions about proper beveling of plywood. Note that I don't plan to laminate the beveled fin with anything, just using the plywood and sanding sealer.

1) The plywood is 1/8" with outer layers 1/32" in thick and a 1/16" inner dark layer. Should I avoid digging into the dark layer when beveling (seems this would not allow for much beveling at all)? If I dig into the dark layer am I compromising the strength of the plywood significantly?

2) What angle to bevel at? Long 10degree taper or just round the edge a little?

I'd appreciate any thoughts on this.

Thanks,
John

Here's a great link for ya... John Coker: Fin Beveling

 

[JohnCoker]

I think it'll be tough to bevel fins that thin with power tools. You could try a sanding block (sandpaper wrapped around a piece of wood) since you're not removing much material.

 

[rharshberger]

I use a black Sharpie to blacken the edge to be bevelled then make small cuts until the black line is as wide as I want the edge to be, I also use a router table with a jig for most fins.

 

[caveduck]

A Dremel Multi-Max oscillating tool with the sanding attachment works great for beveling plywood fins down to about 1/8", and also for sanding the faces flat. I just do it freehand, with a little cleanup using finer grit on a sanding block. Put the fin flush with the edge of your workbench to help keep a consistent angle. The Multi-Max also works fine on fiberglass, where you can use a coarser grit to cut faster. Works best on 5+ ply baltic birch, not so well on lite-ply which I usually avoid. If the center ply seems like it wants to go ragged then the CA mentioned above will make it sand without breaking up. You can bevel thinner plywood down to 1/32" with a sanding drum on a regular rotating Dremel, and the 1/64" stuff with the little sanding discs.

I've seen some number of recommendations for belt sanders or the belt/disc combos as a great way of shaping fins too.

 

[OverTheTop]

I made an adapter to mount my Dremel in a router table. I then made an angled fence to run the fin along. Seems to work quite well.
More details here:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=6030and here:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4758

 

[Donnager]

With the router, fins turn out great. A fine 7 or 15 degree conical, pointed tooth, tungsten carbide bit for wood (McMAster P/N 4257A68 and 4257A69) works well.

Edit--I usually use the 15 degree on 1/16-1/8 fins to keep the edges from getting too fragile. I use the 7 degree on 3/16"+

 

[OverTheTop]

I'll just add here, reinforcing somebody's comment above, do not go for knife-edge thin. Leave a thin flat area on the edge for a more robust rocket.

 

[SolarYellow]

With the router, fins turn out great. A fine 7 or 15 degree conical, pointed tooth, tungsten carbide bit for wood (McMAster P/N 4257A68 and 4257A69) works well.

Edit--I usually use the 15 degree on 1/16-1/8 fins to keep the edges from getting too fragile. I use the 7 degree on 3/16"+

Based on those being noted at McMaster as "red" and "blue," I'm jumping to the conclusion that they are really these:

https://www.foredom.net/product/typ...tapered-shapes-coarse-or-fine-priced-ea-copy/
And you can use Google to find the best price. The Foredom Typhoon burrs have been recommended here before in other threads.

 

[Mopo]

I bevelled my 1/8" plywood fins with a 15° router bit you can find on Amazon. I wanted to give my fins a bit more thickness and meat to bevel so I used some iron-on edgebanding to both side of the fins. I don't have a router table so i just made a 90° surface to clamp my fins to. Using a trim router I adjusted height so about half of the mid layer remained. This gave it the longest bevel possible that I can still round over and not have an overly sharp knife edge.

Pretty happy with the results.

 

[Donnager]

Based on those being noted at McMaster as "red" and "blue," I'm jumping to the conclusion that they are really these:

https://www.foredom.net/product/typ...tapered-shapes-coarse-or-fine-priced-ea-copy/
And you can use Google to find the best price. The Foredom Typhoon burrs have been recommended here before in other threads.

Yes, that is what McMaster sells, and I would only suggest the fine. My experience with the coarse is it left a row of lines in the cut.