The DogSh*t Fillets Thread. A step up from Gravel Fillets.

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Andrew_ASC

UTC SEDS 2017 3rd/ SEDS 2018 1st
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A SAAB Wildman RB-05A Rebuild Story. Because sixteen fillets and a noob doesn't mix. Other mistakes in other builds welcome.

Starting with Leadhead that earned the respect of "Gravel" Fillets.

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Well can't break a broken horrid fillet anymore. Or can I? :facepalm:
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Are you using Rocketpoxy? One thing I have learned is don't over fill the space between the tape. For most of my builds I use a large popsicle or tongue depressor dipped in alcohol to pull fillet. Once you start the pull from either end don't stop until you get to one end or the other.
 
Yeah it's rocketpoxy G5000. I've used the included popsicle stick, still DogSh*t. David had a tip to use alcohol for smoothing which left some fillets less "hole" like and more smooth. I used alcohol. It's better than what it was. The fourth time I've ever touched HPR... The cotronics I've used in past was way runny and actually shrunk.
 
Yeah it's rocketpoxy G5000. I've used the included popsicle stick, still DogSh*t. David had a tip to use alcohol for smoothing which left some fillets less "hole" like and more smooth. I used alcohol. It's better than what it was. The fourth time I've ever touched HPR... The cotronics I've used in past was way runny and actually shrunk.

I've always used the backside of a plastic spoon to pull my fillets. Very easy to do and turn out smooth and straight every time. Keep using the tape like u did, add the epoxy by a popsicle stick, then use the spoon to smooth it out.
 
Another tip is before I apply the epoxy is to let it set 10-15 min. after mixed. It vents out a lot of the air that gives you the bubbles. The Rocketpoxy is nice stuff once you get used to it. You just need a little practice and I am sure you will have great looking fillets. Some guys I know let epoxy set in fillet for awhile before they pull it. I don't. I fill both fillets and than pull epoxy and remove tape right away.
 
CJ says one pull and leave it alone. I use a 18mm estes spent engine case or smaller pvc dipped in denautred alcohol for the pull.

If i dont like how it turns out.. I use the 18mm spentcasing as a sanding block and give the shape some roundness and take off some volume.

When reshaped to something decent i then take a tip from the Wildman and switch to wet sand with 320 grit to blend fillet to tube. It really helps if while pulling the excess epoxy slops onto tape and then you pull tape it will leave a little ridge where it met the tape . Also if epoxy is underpoured a bit the wet sand will smooth out the incedental valleys to where they are almost unnoticeable if it bugs you

Keep the tube nice by sanding on fillet only with the lower grits..and the wet sand with much higher grit at the fillet tube joint

Kenny

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Another tip is before I apply the epoxy is to let it set 10-15 min. after mixed. It vents out a lot of the air that gives you the bubbles. The Rocketpoxy is nice stuff once you get used to it. You just need a little practice and I am sure you will have great looking fillets. Some guys I know let epoxy set in fillet for awhile before they pull it. I don't. I fill both fillets and than pull epoxy and remove tape right away.

I have found that warming the epoxy at this stage with a heat gun helps to level it out and release bubbles.
 
So I had a steak, and got the tape off with less than 3 minutes to spare before it was gonna get "Stuck" like the first time I tried.
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What did you use to pull them smooth?
Doesn't look like there was enough glue to fill the groove or the tool was too large diameter.
 
I used my fingernail to pull the tape up. The popsicle stick radius was too large for application I think. I have a couple of internally rusty ruined metric sockets with smaller diameters that I could try at a future time. Roughed it all up with 60 grit before app.
 
I’ve been using 1” pvc dipped in alcohol. I pull the tape off within minutes of pulling filet.
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A plastic soup spoon or a popsicle stick will work better than the sockets. Its really not all that hard to do. If your going over old fillets they will need to be bigger.
 
What did you use to pull them smooth?

I used the popsicle stick. Perpendicular the epoxy fills it. The extreme corners of the popsicle stick aren't level with fin surface. I could do a second layer tomorrow. There's also epoxy on the internal fin tabs.
 
A plastic soup spoon or a popsicle stick will work better than the sockets. Its really not all that hard to do. If your going over old fillets they will need to be bigger.
+1 cheap plastic spoons, depending on the angle they can form different radius fillets.
 
Might I suggest a few things.

First, you do not want to sand a fillet or other structural composite much. It erodes the strength of the structure you are trying to build.

Secondly, instead of sanding the structural fillet, get an epoxy based filler and make a sand able fillet over the top. Sand this smooth. I like Poly Fibers Super Fill.

Third, get some cheap wood and tubes and practice pulling fillets where it does not matter.




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When does using 60 grit to roughen an existing epoxy fillet count as destroying structural integrity when you apply another fillet over it? I heard it has to be rough surface to adhere too. Maybe I'm wrong. First time I have ever redone fillets.
 
If I sand the entire existing fillet off, and a quarter of a way through the materials I understand I've weakened the structure, but for just roughing up the surface and applying a new layer? I don't get it or your point. Just new.

I'll put another layer on tomorrow this layer dried, but so you can see the fillet itself here.
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To me, marking the surface with 60 grit for a new coat of epoxy isn't structurally destroying a rocket kit. But I'm no composite dork.
 
When does using 60 grit to roughen an existing epoxy fillet count as destroying structural integrity when you apply another fillet over it? I heard it has to be rough surface to adhere too. Maybe I'm wrong. First time I have ever redone fillets.

When you start cutting the fibers technically you are weakening the structure. When you put a fillet over it it is not as good as the tube or plate itself as the fibers and such are not in the same orientation nor matrix. That is the reason for the sandable filler fillet of the top.

I think 60 grit is excessive. I would use something more in line with 180 grit. You want to break the surface tension/ get a good water break for the epoxy to adhere to. I might also wonder is you get more surface area to adhere to by using the finer grit as there are more “grits” per square inch to to speak.




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Alright, I've got 150, 220, 500, 800, 1000, and 1200 grits on hand. I'll start at 150 lightly to get some burrs off then 220 then epoxy it again. There were some other kits that recommended 60-80 grit on fins which is why I started there. That's how we put comp rockets together last year, damnit. This kit had no instructions being scale or whatnot. Well at least I'm learning stuff.
 
it is important to always remember that there is a window in which to bail out of, so to speak. If you lay out some fillets, and they do not look beautiful when they are fresh, they will not look beautiful when they are rock hard, either, and a rag with some acetone will leave you with a fesh canvas again.

Try searching out someone who does beautiful fillets, and watch them do some, closely. Watch what they do, and what their face looks like when they are doing it. Be ultra patient. In cases where something does not come easy, just show up consistently. You might get it. Probably. I would say that you WILL get it, except for the weird reality that some folks just should not touch tools.

Every stroke is a cut....
 
On this particular rocket, I'd recommend a different approach.

I think what you have done is structurally sound. I'd get a tube of bondo and goto town, then sand it smooth slowly.


For future fillets, spoons are great, PVC pipes, etc. there are a few tips I've picked up here I'll try to get good photos of. I'm gonna blow this thing up with photos, but it'll show better detail at this size.

First, I use a sharpie marker to "paint" the small PVC pipe I use. Then I rub it in the fin/airframe joint to make lines. You could also use carbon paper.

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Then, I slowly put down painters tape, careful to make sure the edge is down. I place it on top of the line the tool made. this will make sure the excess is on the tape when you pull, and not on the airframe leaving a ridge.

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I don't have photos of the next step. I use a popsicle stick to lay in the epoxy. starting in the middle of the fillet. You can use the stick to push the epoxy around and make sure it's evenly distributed. don't overfill it. Too much makes it harder. If you pull and there's a gap, you've got time to add more, and pull it again. I load starting at the top of the fin, and typically leave the last inch or two either bare, or with very little. By the time i've pulled that far, it fills in. I start the tool laying right at the front of the fin, where it meets the airframe, then pull it down the airframe in a slow steady manner. Dip the tool in a cup of alcohol, and wipe it clean with a rag. Then carefully peel the tape. Wait a day then rotate.

When making batches of rocketpoxy, doing it on a flat square of cardboard and letting it run out into a flat pool can help minimize bubbles. I do prefer proline 4500 for fillets, but I've used rocketpoxy with some success and only a bubble here and there.

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some other photos-

Leveling the fins-
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Sanding down bondo is super easy with helpers-
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ah ha! found one of the sharpie/ line drawing process
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more tape-

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screwed this one up-

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let it cure, then fixed with epoxy

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Wait wait waaaaaait a second.....

Wasn't this the kid that was trolling MadCow for tolerances to tube measurements???

Then produces this mess?

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Wait wait waaaaaait a second.....

Wasn't this the kid that was trolling MadCow for tolerances to tube measurements???

Then produces this mess?

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Just cuz the kid thinks he knows it all, doesn't mean he does, especially when it comes to rocketry. We may not care for the tone of his posts but when its time to give constructive advice we can do so...
 
Look I can't thank you guys enough for being virtual mentors. We still have not had one for an USRC SEDS team. Two freaking bailed. Combined team experience two multistage flights. Two HPR Kit flights. I'm with the old team that's suppose to babysit the new team and make sure they don't die literally. I did two multistage scratch designs before ever assembling a HPR kit. I bought my first kit after first design to learn more practically. We put many hours into reading apogee and TRF articles and tried to understand weathercocking/Stability margins/ chute sizing. You think I'm bad? We actually cared to not die last year and got a multistage to work enough to win a competition but all you hobbyists still have more experience. This new team they got real arrogant for not even flying an LPR. They said we have designed real missiles what is wrong with CP infront of CG. They can use DatCom, they treat OR and safety codes as a joke. They want to act like OR is an arcade game and HPR is an Estes. And they haven't even flown an Estes. I should just shut up they scare me man. The team I was on last year cared enough to ask. The prof and I were in dismay that some senior students this year ignored advice we had explained directly and bluntly on stability margins. To bluntly put it they were slacking off and did not even bother researching HPR at all for an entire semester. Then after many mistakes it was obvious they did not ask for help nor know how to do anything HPR related. The university is all academia crap and basically they are assigned to read articles on HPR stuff for first semester but my team started design also at that point versus this team didn't even read articles or try prelim then and older team took it more seriously. This newer team acts like doesn't care. And now they know they are behind.

They took a booster from a multistage rocket that my team designed for a heavier sustainer and flew last year, called it an "awesome" idea to slap an H motor and a Wildman cone on it. It simmed 6.8k ft and Mach at 0.328 Stability cal. The prof with an L-1 and I lost it. They finally got their act together this week. I referenced a crap ton of apogee articles to them that we had read on first team that helped us understand just you know the concepts. I might've trolled the darn forum but by end of semester I understood multistages enough not to literally die. I did all the .ork/cad last year and was real conservative with stability margins. 1.7-2.1 per stage and exit velocity excess double of 45fps off 4ft Rail from a tower I also modeled. Bothered to learn FCC and the FAA regs and fin sim. To make matters worse they want to attempt 1x,000ft in April for TRA record because the first team we attempted 20k ft first multistage design flight. Uni is really pushing hard on SEDS/TRA and its all on the students to not screw it up.
 
It can be difficult leading a team. Especially one close in age to yourself, and that thinks they have great plans and everything under control. Tact and mental games become as important as anything else. Try to spend as much time talking about what they did well as what’s wrong. Open with the good. Compliment it. Then cautiously identify possible issues, possible outcomes of those issues, and ask them how they think they could solve it. Lead them to the answer and if possible make them think they came up with the idea.

The attitude youve described isn’t totally uncommon in young inexperienced teams. Gravity is a tough bitch when it comes to grading. They’ll eventually learn.
 
Two of the most important lessons here I believe Andrew is learning:

Patience. Don't need to rush thru things, despite impending deadlines. Rushing just creates new issues to deal with later. Sometimes harder to solve at the later date..

Practice. It's one thing to read a book, solve a bunch of hypothetical problems, understand the 'mechanics' behind the principle /procedure. But when it come time to put actual hand to material, tool to metal (or plastic or fiberglass, or..) nothing prepares or replaces actual "hands on" experience.

And, by the tone of his recent threads & posts, he also seems to be accepting that he has a lot still to learn.

(And please don't embed massive pictures in your posts! just makes it that much harder to read!)
 
Sanded 150 grit then rinsed, fillet only. Going to recoat with rocketpoxy again. DogSh*t gonna DogSh*t.
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Some of these failed radius check.

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Left last set alone.
 
A couple tips:

A gloved finger dipped in alcohol can work well to smooth the edges along the tape.

Remove your rail buttons if possible to make things easier.

Adding micro balloons will make the final layer of Epoxy sand easier.

Thin layers of 3M spot putty is a good way to hide imperfections. Tape off just past the edge of the fillet and apply with a gloved finger. Pull tape immediately and sand an hour later.
 
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