working with epoxy for fin fillets

What is the process for making fillets for fin with epoxy. I know its different than regular glues. Do you do one side at a time both sides at same time?

Thanks, Fred

Check out this... Shows you how to do them like a boss.
https://www.wildmanrocketry.com/pdf/Kits/Wildman/Instructions/EX_DarkStar.pdf

Fred said:

What is the process for making fillets for fin with epoxy. I know its different than regular glues. Do you do one side at a time both sides at same time?

Thanks, Fred

Click to expand...

I get the rocket fairly horizontal and layout two at a time..on opposing fins .

Denatured alcohol is the magic bullet - you mix the epoxy and dribble into the fin joint and draw across till its all filled ..I have used the wood coffee stir sticks and sometimes a toothpick for this. Then get your finger tip wet with the alcohol and run across the fillet front to back. If you get a little on the fin or body tube (or an epoxy finger print) you can try to wipe with paper towel with denatured alcohol on it - don't wreck your fillet trying to wipe..it can be scrapped or sanded off after drying.

Always do the fins 'facing' (on same side) as the lug or rail guides/buttons first as the first set always seems not as good and this 'side' is always away from view when on the pad for pics.

Kenny

It says to use a filler to thicken epoxy? Were does one get that stuff?

Fred

Fred said:

It says to use a filler to thicken epoxy? Were does one get that stuff?

Fred

Click to expand...

I get my shopped fiber from there, he sell in smaller quantity

https://www.ebay.com/itm/141288283952?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Unless you're planning a supersonic or extremely high altitude flight, it isn't necessary to use a strengthening filler. Microbaloons work just fine and add thickness that makes working the fllets much easier. Also, consider using masking tape to delineate the fillet on both the airframe and fin. As soon as you've smoothed them out remove the masking tape. Microbaloons or any filler thickened epoxy will not spread laterally, maintaining a sharp but not raised edge. And finally, don't handle epoxy bare handed. Buy a box of nitrile gloves at your local pharmacy.

I always use some sort of filler when making epoxy fillets. Most often I use thin 20 min finishing epoxy and microballoons. Mix to the consistency of peanut butter. I use a Popsicle stick or gloved finger with denatured alcohol to smooth out. Microballoons are easy to sand. I also have used wood flour and milled glass.


Jerome

KenRico said:

I get the rocket fairly horizontal and layout two at a time..on opposing fins .

Denatured alcohol is the magic bullet - you mix the epoxy and dribble into the fin joint and draw across till its all filled ..I have used the wood coffee stir sticks and sometimes a toothpick for this. Then get your finger tip wet with the alcohol and run across the fillet front to back. If you get a little on the fin or body tube (or an epoxy finger print) you can try to wipe with paper towel with denatured alcohol on it - don't wreck your fillet trying to wipe..it can be scrapped or sanded off after drying.

Always do the fins 'facing' (on same side) as the lug or rail guides/buttons first as the first set always seems not as good and this 'side' is always away from view when on the pad for pics.

Kenny

Click to expand...

You are talking about using a GLOVED finger, right?

JeromeK99 said:

I always use some sort of filler when making epoxy fillets. Most often I use thin 20 min finishing epoxy and microballoons. Mix to the consistency of peanut butter. I use a Popsicle stick or gloved finger with denatured alcohol to smooth out. Microballoons are easy to sand. I also have used wood flour and milled glass.


Jerome

Click to expand...

I'll second Jerome on this one. But I don't use Microballoons or other fillers on most micro & LPR fillets. For MPR models I use Devcon 2-ton 30minute Epoxy and have found an alternative to Microballons for epoxy filler. Go to the 3M website, used to be www.3m.com and request (as some-sort of company) a sample of their GlassBubbles. In the past they have sent a Gallon Bottle of their GlassBubbles for FREE. I've been using from that same bottle for over 6 years and have hardly put a dent in it Works just like microballoons to mix to a peanut butter thickness.

Do ware a dust partical mask when using this product or Microballons, we do not want to be inhaling these micro size glass or phenolic particals. Popsicle sticks dipped in rubbing alcohol or a rubber gloved finger dipped in the same smooth out these thicker fillets on Large models.
For small Micro and LPR fins I don't even bother with the filler using the same procedure in 5-minute Devon epoxy.

I get all of my stuff from U.S. Composites, www.uscomposites.com. They'll have everything you need.

Fred said:

It says to use a filler to thicken epoxy? Were does one get that stuff?

Fred

Click to expand...

Epoxy resin is a base for all kinds of work and joints. We mix things into the epoxy to alter it’s properties to

make strong bonds
fill gaps
make it sand-able
make it spread nice and smooth
prevent it from sagging/running/dripping.

Over the last 10 years I have used around 100 gallons of epoxy resin along with yards and yards of glass and kevlar fabric along with many additives. Mostly building boats but also for all kinds of other projects.

Some epoxy mixtures will cure in 5 minutes and some might take 24 hours if the work space is around 55 degrees. At 30 it won't cure at all but will sit there for weeks with out curing waiting for it to get warm.

Resin/glass/carbon/kevlar and outher additives are available in bulk from companies like West System and Raka.com. I get most of my epoxy products from Raka.com and some special items from sollercomposits.com. At the raka.com site you can find a good right-up on working with epoxy.

https://raka.com/manual.html

To thicken epoxy for fillets, I use 3 additives.

milled glass fibers (to make strong glue)
fumed colloidal silica (to make it flow out smooth)
phenolic Micro balloons (to make it sand-able and prevent it from sagging)

There are may more, pine, maple wood dust, chopped glass strand, cotton, graphite, and many more.

I have been mixing this stuff for a long time with out a recipe but lets start with 1 part by volume milled glass fibers, 2 parts silica add that to some mixed epoxy and mix it all together . You want it to be like thick honey. Next add the micro balloons until it’s thick like peanut butter. We want it thick enough so that it won’t run when we hold the mixing stick vertically.

I think West System has premixed fillet stuff but I have not used it. I don’t use pre-mixed stuff but work with the base additives which allow me build up any compound I need. It takes time to get the hang of working with epoxy and small quantities are expensive. Bulk can cut the cost. An order split by many people keeps the cost down.

Get the hang of working with it and over time you will use it for all kinds of tasks.

Don’t confuse epoxy resin with polyester resin. Stay away from polyester resin. Polyester resin has that strange smell people associate with bondo and generic fiberglass work like a pickup truck top, they use cheaper polyester resin for stuff like that. Most Epoxy resin has little oder and it does not off gas like paint. It’s 2 parts which when mixed become solid. It does not cure by evaporating a solvent. Some solvents are used in the epoxy but only to control it viscosity and volumetric mix rates like 2 to 1 or 5 to 1.

Don't try to use chopped fiber for fillet mix. Chopped fiber is used to fill big hole or gaps. Remember that epoxy is expensive ,fillers are cheap and allow us to stretch our epoxy out making each gallon go farther. For filling larger holes I ofter just use drier lint saturated with epoxy. Fillets need to spread out smooth we don't want bits of fiber stick out. Filets for rocket fins are different then what we use a filet on most epoxy/glass construction. Fiberglass cloth does not like to press into an inside corner. It tends to lift up and then pull air under the cloth taking epoxy away from the joint. The fillet is there to make a smooth curved surface for the fiber glass to flow along preventing it from lifting and pulling in air. In general, it's the glass/kevlar/carbon fabric which provides strength. The epoxy is just the matrix which encapsulates the fiber. It's just like concrete having steel rebar inside. It's the concrete which keeps the rebar steel in tension. A small fillet for holding a rocket fin will likely have enough holding power with out glass on top but for a bigger rocket, a small fillet with 2 or 4 ounce glass on top will be much stronger then a fillet alone and the weight of 2 ounce per yard cloth is almost zero.