Plywood fin finishing?

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Hi, all…
I’m making my first foray into the world of high-power rocketry as I build the LOC 4” V2 in pursuit of Level 1 certification. Got some construction questions for the group:
- Can you paper plywood fins?
- LOC instructions specify 3M ScotchWeld 1838 epoxy. The stuff is expensive! Any advice or opinion on this particular product or suggestions for alternates?
- Any other advice on constucting the LOC kit would be most welcome!
Thanks in advance for any and all replies!

Bruce J…Out!
 
I don't have a clue, but since I was wondering how in the world you could make a nice, smooth, rounded leading edge (much less a sharp edge for supersonic) on plywood, I'll just say "Hi" and see what you find out!

I have family in Winter Haven...
 
Can you paper...yes....do you want to....absolutely not.
After sanding, I rub it with Bondo 907 Glazing and Spot putty. Sand again. Prime and sand as needed.

If you want to know about what to use for adhesive, do a search. There are tons of threads about glue.
 
For the plywood fins, you can use any number of wood fillers including Elmer's Wood Filler or MH Ready Patch. If the former, you can also use it mixed with a little bit of water to fill the body tube spirals. I would then recommend a high build primer (I like Rust-Oleum 2x Primer). Apply the primer, sand, apply again and keep going until you're satisfied with the finish.
As far as epoxy and the price: welcome to high power. My preferred epoxy is Glennmarc G5000 (Rocketpoxy), but it's not available currently. Don't skimp on your epoxy. Do a search on TRF and you'll find hundreds of glue threads.
 
I'm guessing the Scotch epoxy is to bond the fins to the plastic tail cone. Regular epozy has problems bonding to plastics. For wood and.cardboard joints, BSI 30 minute epoxy will be fine.

An alternative might be this new G Flex epoxy from Apogee. I tried it yesterday making fillers on centering ring to motor tube joints. It seems like good stuff and is likely a replacement for Rocket Epoxy.

https://www.apogeerockets.com/Building-Supplies/Adhesives/G-Flex-655-8-oz
 
I'm guessing the Scotch epoxy is to bond the fins to the plastic tail cone. Regular epozy has problems bonding to plastics. For wood and.cardboard joints, BSI 30 minute epoxy will be fine.

An alternative might be this new G Flex epoxy from Apogee. I tried it yesterday making fillers on centering ring to motor tube joints. It seems like good stuff and is likely a replacement for Rocket Epoxy.

https://www.apogeerockets.com/Building-Supplies/Adhesives/G-Flex-655-8-oz
JB Weld PlasticBonder (tan or black color) works quite well for plastics. I built a PML Mini BBX and used it to tack the fins in and do the fillets. Also used it on a few Mach1 kits.
 
For filling fins, I prefer a polyester-based body filler, such as U-Pol Fantastic or their Fibral-Lite. Both use cream hardener, which is basically benzoyl peroxide with a blue dye. You put however much you need on a scrap piece of cardboard, then apply approximately 2% cream hardener and mix well. Spread over the surface to be filled, wait 20 minutes, then you can sand and prime. The Fibral-Lite makes great fin fillets, as it has chopped 'glass instead of talc for a filler. I usually use either an oscillating too with a sanding head, or a palm sander, for smoothing out the glaze.

I used to use spot and glazing putty (the red stuff that smells like acetone), but stopped after being introduced to Fibral-Lite and Fantastic by the guy that does all the body work on Der Red Maxine. He tends to use high-solvent lacquers for painting and told me to avoid the red stuff for a couple of rockets he's painted for me The red stuff soaks up the solvent too much and swells. Besides, I'm not a big fan of inhaling acetone. (Yes, I definitely wear breathing PPE rated for organic vapors when applying polyester-based fillers.)

Harbor Freight sells plastic putty spreaders for about $8 for a box of 20. If you make sure to clean them up (you can sometimes just bend them to get the filler to pop off the plastic spreader) after use, you can reuse them a couple of times.
 
I would never paper ply fin. But that is just me. I would use 3/4oz glass cloth. For that rocket ply is fine for strength. The cloth will give a good surface for finish without adding much weight. Epoxy will stick to it for attaching fins to body. You can make a sharp LE and then wrap cloth around it from both directions. After applying cloth prime and paint as normal.
 
Hi, all…
I’m making my first foray into the world of high-power rocketry as I build the LOC 4” V2 in pursuit of Level 1 certification. Got some construction questions for the group:
- Can you paper plywood fins?
- LOC instructions specify 3M ScotchWeld 1838 epoxy. The stuff is expensive! Any advice or opinion on this particular product or suggestions for alternates?
- Any other advice on constucting the LOC kit would be most welcome!
Thanks in advance for any and all replies!

Bruce J…Out!
- Can you paper plywood fins? - I would first sand them smooth down to about 400 grit. As for papering, yes, sort of. I've never tried the normal paper and wood glue but I have used file folder materials and T-88 or BSI 30 min. epoxy.
- LOC instructions specify 3M ScotchWeld 1838 epoxy. The stuff is expensive! - Get yourself some BSI 30 min. epoxy or T-88. T-88 is the stronger of the two with more working time but it cures slowly.
- Any other advice on constructing the LOC kit would be most welcome! - LOC kits are great, just test fit everything before gluing. 99% of the stuff will fit great but every once in a while you need to sand.
- When finishing the nose cones, sand with 400 grit wet/dry then clean with rubbing alcohol. Spray on either adhesion promoter or an etching primer before the final paint color.
- If the Body tube has deep grooves or is really wavy, you might want to fill, sand and primer the body tube before attaching the fins.
 
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Plywood fins - just sand with 400 then apply 2-3 good coats of filler primer such as Duplicolor, sanding with 400 between coats. Then paint.
Epoxy - even 5 min from wal-mart is stronger than plywood or cardboard. The TV series is built with 5 min epoxy. Get the 8 oz set, the cartridges are way too expensive. Tubes and plywood break before the epoxy fails. I do remove the glassine where the epoxy goes.
 
If you're going to glass the fins, use an epoxy that cures fairly hard. East, West, Raka etc. Or maybe something for laminating. For a couple of days, scraping will be better than sanding. I've seen some very pretty finishes that were paint or lacquer over 3/4 oz glass over balsa. A guy I knew used to wait weeks for the lacquer to dry before buffing. Once you've got it all buffed up like that, do not fly it or you'll scratch it.
 
Hi, all…
I’m making my first foray into the world of high-power rocketry as I build the LOC 4” V2 in pursuit of Level 1 certification. Got some construction questions for the group:
- Can you paper plywood fins?
You didn't say what kind of plywood but since you are building a kit I assume you mean good model airplane plywood. The plywood I've used started out very smooth so spray primer was good enough for me. You could paper them but I don't think the benefit would be worth the trouble.
 
For filling fins, I prefer a polyester-based body filler, such as U-Pol Fantastic or their Fibral-Lite. Both use cream hardener, which is basically benzoyl peroxide with a blue dye. You put however much you need on a scrap piece of cardboard, then apply approximately 2% cream hardener and mix well. Spread over the surface to be filled, wait 20 minutes, then you can sand and prime.
How do you guesstimate 2% for the hardener for the smallish amount needed for fins? I have some U-Pol Fantastic that I haven't used yet, but a project will need some soon. Is it real sensitive to getting the amount of hardener "just right"?

Hans.
 
How do you guesstimate 2% for the hardener for the smallish amount needed for fins? I have some U-Pol Fantastic that I haven't used yet, but a project will need some soon. Is it real sensitive to getting the amount of hardener "just right"?

Hans.
Nope. The hardener is a catalyst, not an active component like epoxy hardener. For an inch to 3 inch puddle of putty, I draw a thin line from the middle to one edge of the circle, then mix thoroughly. If you don't use enough, it takes longer to cure. If you use too much, it cures more quickly and might develop pinholes that you have to go back and fill again.


 
Hi, all…
I’m making my first foray into the world of high-power rocketry as I build the LOC 4” V2 in pursuit of Level 1 certification. Got some construction questions for the group:
- Can you paper plywood fins?
- LOC instructions specify 3M ScotchWeld 1838 epoxy. The stuff is expensive! Any advice or opinion on this particular product or suggestions for alternates?
- Any other advice on constucting the LOC kit would be most welcome!
Thanks in advance for any and all replies!

Bruce J…Out!
Yes you CAN paper fins but why would you want to? The fins are already laminations of sliced sheets of wood and far stronger than paper. What I do is pretty simple: shape the fins as desired with a power sander, fine sand the surfaces, then apply 2 coats of sealer and sand with fine paper. Some people like to add additional epoxy/fibreglass on the fins themselves or go tip-to-tip fibre glassing after the fins are attached to the body.
 
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Hi, all…
LOC instructions specify 3M ScotchWeld 1838 epoxy. T

Bruce J…Out!

That is very important to Bond the wood to the plastic Boat Tail.
Most all other epoxies will not fully stick to the plastic that the Boat tail is molded out of

Use Bob Smith or Zap epoxy 15-30 min for the wood to wood/wood to kraft tube joints.
Use the 3M 1838 for wood to the plastic
 
LOC plywood fins, I don't use spread on filler, and I certainly would not paper.

In the past I sprayed polyurethan wood sealer on them after good sanding. Used steel wool pads with no soap to buff them out, spray again & buff with steel wool pad till glass smooth. Then Paint.

I would do this before they are glued to the rocket, with masking over the fin tabs and roots.

Now, I'm just sanding good, then using high filler paint primer, and then paint. Can you still see the grain? Yes, but I am not worried about that so much anymore.
 
For the plywood fins, you can use any number of wood fillers including Elmer's Wood Filler or MH Ready Patch. If the former, you can also use it mixed with a little bit of water to fill the body tube spirals. I would then recommend a high build primer (I like Rust-Oleum 2x Primer). Apply the primer, sand, apply again and keep going until you're satisfied with the finish.
As far as epoxy and the price: welcome to high power. My preferred epoxy is Glennmarc G5000 (Rocketpoxy), but it's not available currently. Don't skimp on your epoxy. Do a search on TRF and you'll find hundreds of glue threads.
FYI, Aeropoxy ES-6279 is virtually identical to Rocketpoxy, which I have given up on trying to purchase (I've called the manufacturer multiple times and they never know when they might again be able to make it). It is hard to find, but not impossible. I last bought it from Aircraft Spruce & Specialty Company. https://www.aircraftspruce.com/catalog/wppages/es6279adh.php

It's a model airplane supplier. It's pricey, but worth it in my opinion, as it produces the best fillets with ease.
 
FYI, Aeropoxy ES-6279 is virtually identical to Rocketpoxy, which I have given up on trying to purchase (I've called the manufacturer multiple times and they never know when they might again be able to make it). It is hard to find, but not impossible. I last bought it from Aircraft Spruce & Specialty Company. https://www.aircraftspruce.com/catalog/wppages/es6279adh.php

It's a model airplane supplier. It's pricey, but worth it in my opinion, as it produces the best fillets with ease.
The Aeropoxy is good stuff. Of course, you'll spend close to $150 for a quart kit. I, personally, can save on shipping, if I drive to Peachtree City for about an hour and a half one way. Usually, I try to do that when I'm going to be in the area anyway for work.
 
For Level 1, TBII works great and lighter than epoxy. Otherwise, I use BSI which does a better job at resisting Catos than glue.

For my LOC AMRAAM, I was gonna paper but then decided to tip to tip FG the fins.

IMG_4439.jpeg
 
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I like “Delta Creative Ceramacoat Prep All Purpose Sealer” for sealing balsa and plywood fins. It’s cheap and available at craft stores and amazon. It requires a few coats. It’s also water based, so each coat dries in about 10 minutes, and cleanup is very easy.
 
If ply is sealed should not be able to warp. I have ply fins the size of a VW, not warped. And I live in the land of 50,000 mosquito ponds.
 
50,000 mosquito ponds
Not even close....😂

It is believed Brazil, Indonesia, Malaysia and Thailand have the highest numbers of mosquito species. Australia, Indonesia, Philippines and Brazil are recorded to have the highest number of endemic species. However, it is the whole of Africa, South America and Asia where most of the mosquito-borne diseases occur.
https://www.ilctraveloutfitters.com/mosquitoes.htm#:~:text=It is believed Brazil, Indonesia,in Latin America and Asia.
 
The plywood is NOT the same as the balsa you are used to. It is MUCH stronger, and if you are wanting to shape it, MUCH more difficult to sand. Papering wont add any strength or stiffness the way it does with balsa, but it could reduce your finishing the same if thats what you are going for... but not by much.

You *could* paper the fins, but you might get more mileage out of glassing them instead. If nothing else, it is a HP skill you will probably need sooner or later, so I'd recommend diving in while you are on level 1 motors and building a rocket that doesn't have to be "perfect".

do not fly it or you'll scratch it.
best advice Ive seen on this forum lol.
 
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