Masks for making round fillet “points”

[BDB]

When making epoxy fillets, I make an angle with small scraps of tape at the front and rear of the fin (sorry I don’t have a pic). I then use a ton of Bondo to shape it into a smooth curve.

I’d like to get it right the first time. I’m thinking of ways to make a curved mask out of masking tape by drilling a 1/2” hole in some masking tape and then cutting it in half. The mask could be used at the leading edge of my Fiber Red Max to help make a curve for the fillet.

Does any one else have any tricks to do this?

I want this....
to look like this....


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[tightwad]

I just use my finger and a little sanding to get fillets to look good. I guess it is old school, but for me it works.

 

[stealth6]

Here's how I do it -

First off, I use some sort of rounded tool to pull my fillets....usually a short length of pvc tubing, or a dowel, or somesuch. If you think about it, that diameter (half of which determines the size of your fillets), just happens to be exactly the diameter of the circular "points" that you would be looking for. So, I "trace" the outline of that round tool into masking tape with my exacto knife, effectively cutting out the mask that I would want to use. I do one (half circle) for each end of the fillet, and then apply those masks to the airframe right in front of and behind the fin root. Then it's simply a matter of applying a straight piece of masking tape on either side, lining up with the outer edges of the half-circle masks. If I do this right (which is not particularly difficult to do), when I pull my fillets the edge of the tool that touches the airframe lines up pretty much dead on.

If I'm really going for "perfect", some post-cure sanding is usually in order, but for "everyday/regular" type of work, it works fine as is.

This is the same method I use for painting masks as well, by the way.




Works for me, give it a try,
s6

 

[markkoelsch]

I use tape masks at times. Most of the time I do that section light with structural epoxy, and they do the bulk of the shaping with Super Fill.


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[dr wogz]

Fillet with fillet epoxy & 'my special tool' (an old hotel room key..) Pull radius into fillet, drag tool & goo off tip of fin, to get tapered transition. wipe up any runs or spills or.. Let dry / cure. sand, then sand a bit more with a rolled up piece of sand paper. tight roll, about the dia of the fillet. carefully round into the forward transition. Add Bondo. Repeat sanding, repeat bondo & sanding (By now, the sand paper is about they size ofa postage stamp, and very flexible & worn. it adapts to my finger and the curves it's trying to form).. after about 3-5 sanding / bondo passes it's good enough!

 

[BDB]

Fillet with fillet epoxy & 'my special tool' (an old hotel room key..) Pull radius into fillet, drag tool & goo off tip of fin, to get tapered transition. wipe up any runs or spills or.. Let dry / cure. sand, then sand a bit more with a rolled up piece of sand paper. tight roll, about the dia of the fillet. carefully round into the forward transition. Add Bondo. Repeat sanding, repeat bondo & sanding (By now, the sand paper is about they size ofa postage stamp, and very flexible & worn. it adapts to my finger and the curves it's trying to form).. after about 3-5 sanding / bondo passes it's good enough!

Thanks everyone. The method that Dr W uses is pretty much what I do. My round tool of choice is a plastic spoon.

I guess I’m just trying to see if it can be done without Bondo. Maybe we’re all in the same boat.

(But I’ve always been jealous of the way s6’s fillets look.)


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[dr wogz]

Bondo, you always need Bondo..

 

[stealth6]

Nope, no Bondo needed.

If you use the right epoxy (Rocketpoxy works great), along with the proper thickener IF necessary (I use silica, not micro-ballooons), you can get near-perfect fillets with maybe some sanding.

I have used Bondo/filler once or twice, and this is a valid method, but it is not actually necessary and you can get excellent results without it.

s6

 

[Banzai88]

I fillet with 4500. I usually leave a smallish blob of stuff at the back of the fin and shape it with sandpaper upon curing (overnight). Limits the amount of bondo spot putty needed, usually just a skim coat to cure the tiniest of imperfections.

 

[BDB]

I love Rocketpoxy, but like I said, I’m addicted to Bondo. Admitting it is the first step towards fillet freedom....


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[Cl(VII)]

A wide Radius scoopula is an excellent fillet tool, and I assume you have ready access to a plethora of them. I use Aeropoxy thickened with milled fiberglass for most fillets.

 

[oddmanrockets]

I've never used tape masks for fillets I've mainly used straight epoxy and either my finger dipped in rubbing alcohol or a popcicle stick Sometimes I will put micro balloons into the epoxy

 

[dr wogz]

I tend to use West systems 105 & their 407 filler to make my fillets. that being said, I don't sue a tonne of Bondo, just enough to fill the little imperfections.. (there's always a few..)