Taping For Fillets?

I've seen people post about taping the fins and tubes for epoxy fillets. I get that full concept. I was wondering about the technique for this.

I'm using green body shop paint masking tape. Really professional, good stuff. I'm using BSI 30 min epoxy.

So should I be applying the fillets to both sides of a fin at once, or to one side of two so the they face upwards? How long after applying the epoxy before I pull the tape? How long before I should look at rotating it?

And anything and everything else you can think of to make them cleaner and more even. I'm trying to improve my filler work. I've never been great with epoxy fillets.

You should not need fillets.
I never make them anymore.

They alone weigh down a tail section just as much as lightweight fiberglassing ever did.

I've even used FG fillets, and then just sanded them down so you can't see them.
I'm not a performance junky, but after reading a bunch of NACA documents, I understand that rocket shaped objects benefit from not having fillets.

To mark out where to place the tape take some carbon paper and using the same diameter dowel that you will use to make the fillets place the carbon paper on the fins and BT and draw it back with the dowel to mark the tube and fin for where to place the tape.

As for not needing fillets, that is subjective and personal based on what you are trying to achieve.

I use fillets for aerodynamics, appearance, and added strength. Whether it makes a difference to strength or aerodynamics is secondary as the appearance on it's own is enough for me to make that decision. As for adding weight, sure that is a valid point but depending on your goals you can mitigate that by adding micro-balloons, which will lighten and thicken the fillets, at the expense of strength.

As much as I like the refined look of fillets and don't even mind the process of making them, the part of the build I loathe is sanding, filling, priming, filling, sanding priming to blend in the fillets. I literally just spent 3 hours sanding down two fillets, fin/BT area on my 3" Darkstar that I am repainting. The thought of 1 more fin and 1.5 hours of my life gone that I will never get back is something I am not looking forward to. But I find the end result rewarding!

mpitfield said:

To mark out where to place the tape take some carbon paper and using the same diameter dowel that you will use to make the fillets place the carbon paper on the fins and BT and draw it back with the dowel to mark the tube and fin for where to place the tape.

As for not needing fillets, that is subjective and personal based on what you are trying to achieve.

I use fillets for aerodynamics, appearance, and added strength. Whether it makes a difference to strength or aerodynamics is secondary as the appearance on it's own is enough for me to make that decision. As for adding weight, sure that is a valid point but depending on your goals you can mitigate that by adding micro-balloons, which will lighten and thicken the fillets, at the expense of strength.

As much as I like the refined look of fillets and don't even mind the process of making them, the part of the build I loathe is sanding, filling, priming, filling, sanding priming to blend in the fillets. I literally just spent 3 hours sanding down two fillets, fin/BT area on my 3" Darkstar that I am repainting. The thought of 1 more fin and 1.5 hours of my life gone that I will never get back is something I am not looking forward to. But I find the end result rewarding!

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Good points all, and I was not trying to say that any method was necessarily more appropriate for any given application, but no one had answered the thread, so I chimed in.

I do mine one side of two fins. I pull tape after the 30 minute set time, then rotate and do two more, etc. Can do all three fins in 1.5 hours.

I've used regular masking tape, blue painters tape & green bullfrog tape for fillets. Don't think it matters which you use as long as you pull up the tape before epoxy sets.

timbucktoo said:

I've used regular masking tape, blue painters tape & green bullfrog tape for fillets. Don't think it matters which you use as long as you pull up the tape before epoxy sets.

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Do you mean "sets" or "hardens?"

Bat-mite said:

Do you mean "sets" or "hardens?"

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Sets. If epoxy runs over tape, it's much easier to remove tape. Otherwise if you let it harden and epoxy runs onto tape, it's a lot of work removing tape from under the hardened epoxy. Ask me how I know.

mpitfield said:

To mark out where to place the tape take some carbon paper and using the same diameter dowel that you will use to make the fillets place the carbon paper on the fins and BT and draw it back with the dowel to mark the tube and fin for where to place the tape.!

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Got this one covered. I used 3/16" tape to measure from the joint out and up for the green tape.

mpitfield said:

As for not needing fillets, that is subjective and personal based on what you are trying to achieve.

I use fillets for aerodynamics, appearance, and added strength. Whether it makes a difference to strength or aerodynamics is secondary as the appearance on it's own is enough for me to make that decision. As for adding weight, sure that is a valid point but depending on your goals you can mitigate that by adding micro-balloons, which will lighten and thicken the fillets, at the expense of strength.!

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I use fillets for strength and aesthetics. I find it hard to believe that a root edge bond is enough for near Mach flights. Maybe, possibly, for ttw fins, but certainly not surface mounted fins.

The entire rocket looks clean and nice and even when the fillets are smooth and equilateral.

mpitfield said:

As much as I like the refined look of fillets and don't even mind the process of making them, the part of the build I loathe is sanding, filling, priming, filling, sanding priming to blend in the fillets. I literally just spent 3 hours sanding down two fillets, fin/BT area on my 3" Darkstar that I am repainting. The thought of 1 more fin and 1.5 hours of my life gone that I will never get back is something I am not looking forward to. But I find the end result rewarding!

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It's worth the extra work to get a finish with no seams. I'm not there yet, but getting closer.

Bat-mite said:

I do mine one side of two fins. I pull tape after the 30 minute set time, then rotate and do two more, etc. Can do all three fins in 1.5 hours.

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So on a four fin rocket, lay it up with two fins at 45°, fillet base to tip, then leave it so the epoxy sits in a valley, right?

So what do you do on the opposing side to make the fillet even as you round the lading edge of the fin? Cause one side is set and/or hardened, now you have to make the new side blend into it.

Bat-mite said:

Do you mean "sets" or "hardens?"

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timbucktoo said:

Sets. If epoxy runs over tape, it's much easier to remove tape. Otherwise if you let it harden and epoxy runs onto tape, it's a lot of work removing tape from under the hardened epoxy. Ask me how I know.

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I've been told that if you pull the tape just a hair early, that the tape line can flow out and disappear without extra sanding. Dunno the truth of that yet.

TopRamen said:

Good points all, and I was not trying to say that any method was necessarily more appropriate for any given application, but no one had answered the thread, so I chimed in.

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Hey NP Top, I was adding my .02 to to the cause.

timbucktoo said:

Sets. If epoxy runs over tape, it's much easier to remove tape. Otherwise if you let it harden and epoxy runs onto tape, it's a lot of work removing tape from under the hardened epoxy. Ask me how I know.

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Ah yes I forgot about that part of the question.

For me it depends on the fillet material, but the goal is to remove it before it hardens to the point where pulling the tape is a problem. I use different epoxies for different applications including using different additives, like micro-balloons for a filler/thickener, chopped glass of carbon fiber for strength.

In each case the time differs when the epoxy is set enough that pulling the tape will not allow it to flow to another area. Ideally you want to pull it when the epoxy is just at the point of being set and still flowing. That way when you pull the tape the edge flows down but does not flow everywhere, if you know what I mean.

You could mix up a small batch on a bit of paper, in the same environmental conditions as you plan to do your final work. Then check it every once in a while to test it for the ideal set time, then do your production run.

Having said that I wouldn't stress about the tape because when you sand the fillet, which I do with a dowel or different size and shape sanding blocks wrapped in progressively finer sandpaper, the process usually removes any left over tape from the masking.

If you use filler it will thicken the epoxy and make it possible to pull the tape immediately after smoothing the fillet. This will completely eliminate any ridge from forming at the edge of the fillet. Probably the best for this is the West System fairing filler. It also reduces the volume of epoxy producing a lighter fillet.

BTW here is a set of sanding blocks that I cannot live without, when it comes to fillets.

https://www.leevalley.com/US/wood/page.aspx?p=20183&cat=1,42500

The angled set "C" on the right in the picture, specifically the thinner middle one, is the most utilized one for me. That and the convex set. I have yet to use the concave blocks.

I never tape before doing fillets. I don't see the purpose, tape will just create an unwanted edge on the epoxy fillet. Without tape I am able to make it perfectly smooth fillets without edges. I also don't use any tools for sanding fillets other than my finger.

I've shaped my fillets with a piece of PVC pipe wetted with isopropyl, for a smaller rocket (38mm MD) I used a plastic spoon. I always do a pair of fillets at a time, and generally wait at least an hour (assuming ProLine 4500 or 30m Z-poxy) before rotating to the next set. More typically (when I'm not in a hurry) I do one in the evening then the next one in the morning before heading to work, so each one gets 8-12 hours before I move to the next

To figure out where to place the tape (assuming I'm going to paint the rocket to cover it up later) I mark the end of the pipe/spoon with a red sharpie and then drag it along where I'm going to make the fillet, it transfers enough of the sharpie to the fin and tube to see where to place the tape (the sharpie rubs off the pipe/spoon when applying the alcohol). If you trust yourself to lay a straight line you can just mark the two ends of the fillet area, don't have to drag the sharpie down the entire joint. On a colored FG rocket I wasn't going to paint I eyeballed it, just have to get the tape line straight/flat and what looks parallel to the mating line.

I don't think the type of tape matters, it's just for masking and the epoxy won't seep under like paint can (or even if it did it's so little you wouldn't see it). So I wouldn't waste any expensive tape for this, blue tape is all I've used but regular masking tape should be fine as well (I just don't have any). Of course if taping cardboard make sure it's a tape that won't take any of the paper off with it.

I tend to use more epoxy than I need, so a bit squeezes out onto the tape when running the pipe along it, so I pull the tape as soon as the fillet is smooth to ensure none of what squeezed out runs back down into the fillet area.

For me the trickier part is above and below the fin. I mask-off a triangle (45-90-45) above and below and try to shape things with the pipe and more often end up doing further shaping with my finger, but I find it tough to get this to turn out as well as the rest of the fillet, which I've been very happy with.

woferry said:

assuming ProLine 4500

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I don't know about the rest of you but I find the ProLine 4500 the easiest epoxy to work with for fillets. It is the one epoxy I work with where if I remove the tape at the right time the edge just blends into the fin and body. I know some of you just leave them as is, and they look fine without any sanding, that is if you don't get any bubbles.

Nathan said:

I never tape before doing fillets. I don't see the purpose, tape will just create an unwanted edge on the epoxy fillet. Without tape I am able to make it perfectly smooth fillets without edges. I also don't use any tools for sanding fillets other than my finger.

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If anyone has seen Nate's builds he is in a different league, most of us need all the crutches we can get our hands on and our builds still don't look as good as his.

I used the ProLine in the no-paint case, the black fillets looked great on the black fins and red body (except for where I accidentally got a drop or two on the body, that stuff never totally wipes off for me). I concluded that when working with the stuff I should tape off EVERYWHERE I don't intend to put the epoxy, just to be sure. Elsewhere I'm more likely to use the Z-poxy when I know I'll be painting over it. I've never done any sanding of my fillets other than to rough it up a bit for painting.

I love proline for filets. They always come out finished- no sanding or retouch needed. I do two fin sets per pass over three runs for three fin rockets. i level my rocket side ways and length wise as the epoxy wants to be level. I mask at the pre determined outside edge of the filet. The purpose of the tape is to stop oops from getting where i don't want it. i remove the tape when the epoxys still very wet- if you wait until it begins to harden you will have a tape line, wait way to long and tapes embedded. gravity is your friend- use it! Tapers: a tool to pick up spilling area and alcohol wipe for oops. I avoid trying to work epoxy dragging it as i simply so a very slow pour adding where needed instead.

I use Aeropoxy Light for my fillets. It's thick so after 15-30 minutes of curing it will not run. The epoxy adds some strength but noting like Proline. I have never had a fin failure because of a weak fillet so I know Aeropoxy light is a good option. I wet my finger with water and slide it down the Aeropoxy it makes for a very smooth fillet. I normally tape as others have mentioned and use a spoon to get the desired curve. I pull the tape after 15-20 minutes. If any sanding is required I normally do 320 followed by 500.

I haven't done alot of epoxy fillets but I found these two older tutorials very helpful and informative.

https://www.skypirate.net/rocketry/con_fil_01.htm

[video=youtube;mIyl4OPotgM]https://www.youtube.com/watch?v=mIyl4OPotgM[/video]


I used 30 minute hobby store epoxy thickened with balsa dust and talc, cause that's what I had on hand and I'm frugal (or cheap :blush. I judged that I didn't need any of the fancier additives for my purpose (3, 3.5 lbs rockets flown with H impulse to date). I pulled the tape as soon as I was satisfied with the shape so I had no epoxy dam to speak of.

There's a number of build threads that highlight how taped fillets happen. CJ's DarkStar build thread is a basic encyclopedia of building most fiberglass rockets... Definitely worth checking out. Also, I did a build thread on the Demon 98 where I detail my fillets and techniques.

Below is a link to the same method I use which I picked up from the my GLR Mariah38 instructions.

The kit literally comes with the carbon paper and a couple of dowels. Since then I picked up a small box of carbon paper that will last a lifetime, and a few different sized dowels. I have used this method with Aeropoxy ES6209, Aeropoxy ES6209 mixed with chopped FG, Aeropoxy ES6209 mixed with chopped CF, Red Baron 30minflex cure, Red Baron 30minflex cure mixed with chopped FG, Red Baron 30min flex-cure, Red Baron 30min flex-cure mixed with chopped CF, ed Baron 30min flex-cure, Red Baron 30min flex-cure mixed with micro-balloons, Proline 4500 and Proline 4500 mixed with chopped CF.

In the case of the Proline 4500 I don't use the wax paper. This is because of what I mentioned in my previous post and what others mentioned as well, it flows and settles so nice that you can simply run a dowel/finger over the fillet, no wax paper, then remove the tape when still slightly flowing

[video=youtube;ZeJiTHnZlRk]https://www.youtube.com/watch?v=ZeJiTHnZlRk[/video]

It's going to be a learning curve. I'm glad I have two to practice on before I get to the two that seriously matter. Thanks for the info. I'll be studying it up over the next couple of days.

This Sunday (weather permitting) I'll be doing two crap tons of rocketry work. Got a launch this Saturday. And one next Saturday. And a school outreach launch the following Thursday. How in the heck am I gonna be ready for NSL? lol

mpitfield said:

BTW here is a set of sanding blocks that I cannot live without, when it comes to fillets.

https://www.leevalley.com/US/wood/page.aspx?p=20183&cat=1,42500

The angled set "C" on the right in the picture, specifically the thinner middle one, is the most utilized one for me. That and the convex set. I have yet to use the concave blocks.

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i had seen these someplace before and needed them for a woodworking project. I asked for them at Rockler, they could figure out what I was looking for. Thank you! I will be ordering a set.

I use rocketpoxy (G5000) for my fillets and pull the tape right after I run a large tongue depressor down the fillet to smooth it. That way the epoxy you squish out onto the tape doesn't gravitate back into the fillet. With smaller rockets, I will use a popsicle size stick to smooth the fillet.

For me, no tape. An old hotel key card cut to the right radius I want for my spatula / forming tool. And filler. Light sandable filler for my epoxy, mixed to a peanut butter consistency. dabble the mix, then smooth out / form the fillet with the key card (the straight edge against the fin help wipe away any unwanted goo.) Any ridge / build up on the airframe is scraped off / wiped up before it has a chance to set. I do one side of two fins, so it 'sags' into the valley. And, practice make perfect.. don't slob it on only to wipe most of it off in one pass... add a bit & add a bit to build up the fillet. Keep the card at the same angle throughout. Clean the card after each pass...

Finger sand, no tools or jigs. A small block maybe (3/4" x 1-1/2" x 1/2" balsa block with one edge radiused). Worn out paper is best, as it won't take too much off. (bends / curls easier too) Fold it a few times to get some rigidity along the curvature. Work at it, light pressure.. a slight twist as you run the paper up & down the fillet.. sometimes working the paper up & down the fillet (rather than along it) helps even out the bumps..

I've heard of people using baby powder for their filler material too.. I've tried 'balsa dust' too, but is lumpy..

There’s one thing that I think we often miss when talking about fillets. We’re real good at telling people WHAT epoxy we’re using, WHAT tape we’re using, WHAT radius to use, and WHAT tools we’re using…..and real bad at telling people WHEN we’re doing something TIMEWISE. When dealing with a material that cures and changes handling properties, order of operation isn’t really descriptive enough.

RocketPoxy or 4500 (and most anything else, for that matter)flows very differently at 30 minutes after mixing than it does 5 minutes after mixing.

I might pull tape 10 minutes after mixing/laying material/shaping and someone else might pull tape 20 minutes after mixing. Either way, chances are we’re going to experience slightly different results because of the way that some epoxies gell up quicker or slower than others.

Add to that heat also makes a difference. Cool it and it takes longer to set up, also longer to 'ooze' out. Heat it up (with a heat gun), it'll run like water & set up glass smooth, but it'll set up in about 5 seconds!

mpitfield said:

Below is a link to the same method I use which I picked up from the my GLR Mariah38 instructions.

The kit literally comes with the carbon paper and a couple of dowels. Since then I picked up a small box of carbon paper that will last a lifetime, and a few different sized dowels. I have used this method with Aeropoxy ES6209, Aeropoxy ES6209 mixed with chopped FG, Aeropoxy ES6209 mixed with chopped CF, Red Baron 30minflex cure, Red Baron 30minflex cure mixed with chopped FG, Red Baron 30min flex-cure, Red Baron 30min flex-cure mixed with chopped CF, ed Baron 30min flex-cure, Red Baron 30min flex-cure mixed with micro-balloons, Proline 4500 and Proline 4500 mixed with chopped CF.

In the case of the Proline 4500 I don't use the wax paper. This is because of what I mentioned in my previous post and what others mentioned as well, it flows and settles so nice that you can simply run a dowel/finger over the fillet, no wax paper, then remove the tape when still slightly flowing

[video=youtube;ZeJiTHnZlRk]https://www.youtube.com/watch?v=ZeJiTHnZlRk[/video]

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OK, effective, but all I can say on this is: FILL-it as in, not fil-LET.