Quantcast

Filleting...

The Rocketry Forum

Help Support The Rocketry Forum:

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
So I thought I accomplished this with my Estes Crossfire. But I got lots of gaps and bubbles. Any tips on how to best do this? Secrets? Tools?

Thanks!
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,565
Reaction score
5
So I thought I accomplished this with my Estes Crossfire. But I got lots of gaps and bubbles. Any tips on how to best do this? Secrets? Tools?

Thanks!
What did you use?

I use Elmer's white glue and my finger.
 

Pippen

Well-Known Member
Joined
Jan 18, 2009
Messages
1,969
Reaction score
3
People do this differently, so take in the ideas and then play around with what works best for you.

I have kids building with us and here's what I have them if they're interested in making neat glue fillets. Works for big kids too. :)

1) Put a strip of blue tape along either side of the fin, leaving about 1/4 inch of space where the glue fillet is going to go. This takes some extra time but it keeps the glue from running or smearing onto the rest of the body tube.
2) We use yellow wood glue as it's less runny--this is my personal preference--others like all-purpose white glue. I transfer glue into smaller bottles with narrow tips because it's much easier to handle and apply to small areas. In fact I got some bottles at Hobby Lobby today in the paint section but I've used bottles I've emptied paint or glitter from as well.
3) Practice running a glue fillet smoothly along a piece of cardboard or paper just to get the feel for it.
4) Run a bead of glue along the fin, keeping it as steady as you can. If you have a spot with missing glue or a big air bubble use the small nozzle on the glue bottle or a toothpick to fill it in or rub it out.
5) Swipe it carefully with your finger. Remove the tape when you're satisfied you don't need another fillet and the glue is dried.

Next?
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
What did you use?

I use Elmer's white glue and my finger.
I used Elmers and a Q Tip. Maybe I just need to be more careful. I have hulk fingers so maybe I can find something else to use. lol
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
People do this differently, so take in the ideas and then play around with what works best for you.

I have kids building with us and here's what I have them if they're interested in making neat glue fillets. Works for big kids too. :)

1) Put a strip of blue tape along either side of the fin, leaving about 1/4 inch of space where the glue fillet is going to go. This takes some extra time but it keeps the glue from running or smearing onto the rest of the body tube.
2) We use yellow wood glue as it's less runny--this is my personal preference--others like all-purpose white glue. I transfer glue into smaller bottles with narrow tips because it's much easier to handle and apply to small areas. In fact I got some bottles at Hobby Lobby today in the paint section but I've used bottles I've emptied paint or glitter from as well.
3) Practice running a glue fillet smoothly along a piece of cardboard or paper just to get the feel for it.
4) Run a bead of glue along the fin, keeping it as steady as you can. If you have a spot with missing glue or a big air bubble use the small nozzle on the glue bottle or a toothpick to fill it in or rub it out.
5) Swipe it carefully with your finger. Remove the tape when you're satisfied you don't need another fillet and the glue is dried.

Next?
The tape sounds like a great idea and the smaller tipped bottles...I think we sell those where I work.

Thanks guys!
 

Pippen

Well-Known Member
Joined
Jan 18, 2009
Messages
1,969
Reaction score
3
I use Elmer's white glue and my finger.
So little fuss and your fillets are probably as good as mine, if not better. :rolleyes:

UfO, it's all about finding what works for you.
 
Last edited:

BsSmith

Well-Known Member
Joined
Jan 18, 2009
Messages
807
Reaction score
0
I make really ugly fillets with glue, so I just use a filler and popsicle sticks to smooth them out. It seems to work really nice. The attached pictures are the fillets on my Talon 3, not exactly low power but the only pictures I have of fillets. I used big popsicle sticks for that, and decided I liked the curvature of my thumb better for sanding. For smaller I use the ends of bic pens.

RP 033.jpg


RP 051.jpg
 

Pippen

Well-Known Member
Joined
Jan 18, 2009
Messages
1,969
Reaction score
3
UfO, just plain glue fillets are functional and with some practice can turn out decent. Some--like Brian just pictured--do like to take extra steps and use wood filler to really make them look good. Not necessary but if you want more info on that, the techniques board is a good place to ask.
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
UfO, just plain glue fillets are functional and with some practice can turn out decent. Some--like Brian just pictured--do like to take extra steps and use wood filler to really make them look good. Not necessary but if you want more info on that, the techniques board is a good place to ask.

Thanks again everyone.

I ran out in the freezing cold garage just a minute ago and tried out the finger method...works fine. Turns out I over thought this one! lol
 

troj

Wielder Of the Skillet Of Harsh Discipline, Potent
Joined
Jan 19, 2009
Messages
14,286
Reaction score
204
There's also a bit of a touch to it that you learn in time.

Some glues are more prone to bubbles and gaps than others, too.

-Kevin
 

Trident

Retired, plenty of kits
Joined
Jan 18, 2009
Messages
861
Reaction score
9
Titebond Trim and Molding Glue works extremely well for glue fillets. No bubbling. Period. I tried this for what I viewed as "utilitarian" builds, where I was not going to be quite so anal about smooth fillets. I've used this with great success. I have not tried to sand it. Rather, I just used it to add a really minimal fillet that looked smooth. I was not trying to do any large blends, as could be done with putty.

Trust me, I've been using Bondo, Squadron Putty, wood fillers -- lots of materials over the years (and epoxy fillets on HPR rockets in the past). I think I'll use this a lot more often now, just for its ease of use.

I found the Titebond at Lowes, but I really had to look. I am not sure if it is new, or I've just never noticed it on the shelves before.
 

jj94

Well-Known Member
Joined
Jan 18, 2009
Messages
4,026
Reaction score
0
I use Titebond III, and love it. Extremely strong and useful. What I do is squeeze a thin line of it along the fin/tube joint. I use my finger to lightly run across it in order to smooth it out. There shouldn't be too much glue excess glue, and if there is a lot, then you used too much. Let it dry and then repeat it. By doing this, you're essentially creating strong layers of fillets. It's strong, neat, and fast. There aren't many bubbles or gaps, if any, since each layer should be relatively thin, equal to a small fillet about 1/16 inch thick. Also, it's faster since the thin layers dry much quicker than one thick fillet. Then, if the fillet isn't smooth as I would want it or I just want them to look thicker for cosmetic reasons, I take wood filler and apply it to the joint. Then use something like the end of a 1/4 inch dowel to smooth it out into one uniform fillet. Then smooth it out after it has dried by lightly sanding it.
 

powderburner

Well-Known Member
Joined
Jan 18, 2009
Messages
7,401
Reaction score
4
I am not even going to start into the aerodynamics of whether you really need fillets on low-power and mid-power rockets. Some folks simply like the looks, others sincerely believe they are doing something structurally good. Let's start there.

If you are adding fillets for structural purposes, don't try to use fillets to make up for a weak fin root joint. If the fin didn't fit well, break it off and start over.

A snug fin root fit is key. If there is good contact between the root "face" and the local BT, it will not take much glue to create a joint that is structurally stronger than the balsa or the cardboard. Glue piled on the outside of the joint is a poor substitute for a well-fitted root joint.

Cut/trim/sand the fin root until it is flat. You don't have to test-fit fin roots to the side of a rocket to check for this, you can use any ol' decent-quality straightedge.

If the fin is thin (compared to the BT diameter), proceed to gluing. If the fin is thick enough that a gap shows under the outer edges (when the fin centerline is snug to the BT), you have some more fitting to do. Wrap a sheet of sandpaper backwards around the BT (that is, grit-side out). Holding the fin in straight alignment with the lengthwise axis of the BT, sand with the centerline of the fin touching the sandpaper. You want to remove the center of the fin root and leave the edges. Check the fin root fit often (with the sandpaper removed). Be prepared to toss improperly sanded fins, and to replace with new fin stock. There is no way around this.

Before gluing the fin to the BT, pencil a mark around the fin root area, and re-mark the fin location line. Sand the BT (using very fine sandpaper) to remove all signs of the plastic glassine coating in the fin root area. This will allow your glue to penetrate a bit better from the balsa to the cardboard. Some people like to punch pinholes through the BT to help glue penetrate even more.

Preglue the fin with a thin layer on the root "face", and press it in place on the BT, then remove and let everything dry. Do this twice if it makes you feel better...but once is enough if you do it right. Assemble by applying a light layer of glue to the root face and re-attaching the fin in the proper place. Check to make sure the fin doesn't sag out of position while this glue dries. There are lots of fin jig ideas out there to make sure the fin remains properly aligned. Some guys use a dab of epoxy or CA at the ends of the fin root--this works too. But there is no way to rush this. If it takes one "setup" (of whatever your alignment tool might be) per day to get a fin right, then you can't rush it. It will take you four days to do four fins.

After the fin is solidly attached, if adding a small fillet of glue makes you feel better, then go for it. Be warned that most white and yellow glues leave pits. It's how they're made. They have water in them. The outer face of the glue dries first, with a bulk of still-wet glue beneath. The outer face doesn't stretch much after it is set up. As the glue beneath dries and loses its moisture, its volume shrinks---and the outer layer of glue can only follow it so far. At some point the outer skinned-over layer tends to open up, causing pits and gaps and bubbles, as well as ridges at the outer edges.

If you are worried about structural strength of your fin roots (i.e. big motor, fast rocket, thin fin, short root chord length, whatever) then plan ahead. Options: (1) redesign for a better fin root geometry (thicker fin, longer chord, etc), (2) design a short fin tab to extend part of the root through the BT (and glue both inside and outside as you install each fin), (3) design a long fin tab to extend part of the root through the BT all the way down to the MMT outer surface (and prepare the outer surface of the MMT BT as above, and glue all joining surfaces as you install each fin), (4) use some harder/tougher wood (like spruce) to shape a root fillet for both exposed corners of each fin (and install these reinforcements before you load up the fin root with glue fillets). I am sure there are other approaches, this is just what I could come up with during this sit-down.

A different subject: if you are adding fillets for aesthetic purposes, building up a big gob of filler on the rear end of the rocket is not a good idea. Also, a hard fillet can cause your fin to crack along the root if the fin takes a good whack during landing. A softer fillet material allows the fin to flex a bit more, and a fillet re-surfacing is an easier repair than a fin replacement.

Assuming you have a decent structural joint between the fin and BT, it is EASY to create fast, smooth, light, repairable fillets of any size. You don't even need masking along the length of the root. Get some light-weight spackle, the kind with microballoon filler where the whole tub feels like it's empty. Lightly sand and clean the root area, smear on the spackle, work it into the joint with your finger or suitable tool, and shape to your satisfaction. This spackle will cover any and all blips and divots in the fin root glue--they will be covered forever. If the spackle gets thick to work with, flick a few fingertips of water onto the joint and work it in. If the edges start to dry out and harden, flick a few more fingertips of water onto the spackle and work it in. Finish by using a wet paper towel to wipe the length of the fillet, wipe and smooth the edges, and to get a preliminary smooth finish. Even after this stuff has been "dry" for 30 or 60 minutes, it is still pretty easy to wipe away unwanted spots with a wet paper towel.

When this stuff dries it is extremely easy to sand and shape. Roll some fine-grit sandpaper backwards around a wood dowel (use a 1/2 inch dowel to get a fillet with a 1/4 inch radius, etc) and stroke the length of the fillet a few times. If you find some low spots, it is easy to add spackle. If you have some high spots, they won't last long. Use finer and finer grit until you are satisfied, and then make a final smoothing with a wetted fingertip.

If you want to toughen the spackle you can soak a little CA into the exposed surfaces. If you want to prime it for paint, it has taken several spray primers very well for me and I expect it will for you too. If you want to paint directly onto the spackle, I have had very good luck with Wmart rattlecans.

Spackle fillets are light, fast, easy to repair, and plenty durable for low-power and mid-power. Try them and I'll bet you switch from epoxy fillets immediately.
 

troj

Wielder Of the Skillet Of Harsh Discipline, Potent
Joined
Jan 19, 2009
Messages
14,286
Reaction score
204
Spackle fillets are light, fast, easy to repair, and plenty durable for low-power and mid-power. Try them and I'll bet you switch from epoxy fillets immediately.
Spackle is something I've never thought to try! That would be the perfect thing to put over an ugly, structural fillet to make it look nice.

-Kevin
 

Pippen

Well-Known Member
Joined
Jan 18, 2009
Messages
1,969
Reaction score
3
Note to newcomers to model rocketry who are reading this: the glue and finger method works just fine for fillets, but as you can see there's plenty of room to grow in skills, obsessiveness, cost, etc. :D
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
42
Location
Washington DC
Ditto Sandman:
Elmer's white glue or Yellow carpenters cement and you finger. if you have large hands and I do, use the little finger;)
 

dr wogz

Fly caster
Joined
Feb 5, 2009
Messages
5,698
Reaction score
929
Location
Land of Poutine!
And, if you can get them.. a 10cc syringe..
I use teh yellow carpenter's glue, althoug it does tend to shrink when curing..

For me, a finger and a rag: to wipe up the extra glue off your finger!

Numerous ruined jeans & shirts from the "glue on finger looking to wipe it off on something" dance..)
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
Thanks for the great info powderburner!

I'm doing this simply for aesthetic reasons at this point. I just don't like the little pit holes I get after painting. I'm going to pick up that spackle. The white glue just isn't working to my satisfaction.

Pippen, that's just my problem when it comes to building model kits of any kind...obsessiveness. lol
 

dr wogz

Fly caster
Joined
Feb 5, 2009
Messages
5,698
Reaction score
929
Location
Land of Poutine!
I have resorted all too often to wiping my glue laden finger on the lower edge / underside of my work table..


What about the "CA face cringe"?! :D

(The fumes of CA wafting up, hits your eyes & nose, causing both to shut & water profusly! You can't run away, because you're holding said part in place or you're glued to said part.. Usually both!)
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
I have resorted all too often to wiping my glue laden finger on the lower edge / underside of my work table..


What about the "CA face cringe"?! :D

(The fumes of CA wafting up, hits your eyes & nose, causing both to shut & water profusly! You can't run away, because you're holding said part in place or you're glued to said part.. Usually both!)
Or maybe you've managed not to glue yourself to that part, you smile, you're proud of yourself, only to find out your fingers are glued together. :D
 

troj

Wielder Of the Skillet Of Harsh Discipline, Potent
Joined
Jan 19, 2009
Messages
14,286
Reaction score
204
And, if you can get them.. a 10cc syringe..
I use teh yellow carpenter's glue, althoug it does tend to shrink when curing..
I have a bunch of 20cc syringes I bought that I'll part with reasonably. No needles.

Numerous ruined jeans & shirts from the "glue on finger looking to wipe it off on something" dance..)
Several beatings from my wife broke me of that habit....

-Kevin
 

troj

Wielder Of the Skillet Of Harsh Discipline, Potent
Joined
Jan 19, 2009
Messages
14,286
Reaction score
204
Or maybe you've managed not to glue yourself to that part, you smile, you're proud of yourself, only to find out your fingers are glued together. :D
If you haven't glued your fingers together, or to something, then you haven't used enough CA yet....

-Kevin
 

dr wogz

Fly caster
Joined
Feb 5, 2009
Messages
5,698
Reaction score
929
Location
Land of Poutine!
for those of you who have syringes:

McMaster Carr "disposeable dispencing needles" #75165A671 $13 for a pkg of 50!

7510A651 for the 10cc syringe..
 

UfO

Well-Known Member
Joined
Mar 18, 2009
Messages
67
Reaction score
0
I picked up some Spackle Light yesterday. I'm going to try it out on my Bullpup build. I'll be sure to update on how it works for me.
 

hcmbanjo

Well-Known Member
Joined
Jan 18, 2009
Messages
2,305
Reaction score
102
If you are doing white glue fillets:
Lay the glue in the fin / body tube joint - slowly. This will help keep air out of the joint.
Keep an eye on the fillet as it dries. Air bubbles will not show up when the white glue is first laid down. You can pop the bubbles when the glue is fairly wet. Use a toothpick, the wood tip will pop the bubble easier than trying to use the tip of your hobby knife.
If the glue is still very wet, it should flow in and fill the hole. If it doesn't, I'd wait until it's completely dry to lay in more glue. You can't add more glue on a half-dried fillet and smooth it out with a finger. Let the first fillet dry, then go again. I typically do three fillet layers.
Be warned, anytime you fillet a launch lug you are bound to get bubbles. That tight angle is nearly impossible to fill without bubbles.
I've yet to try the Epoxy Fixit available through Apogee. I've seen fillets done using this and they look great!
 

jackman

Well-Known Member
Joined
Feb 12, 2009
Messages
98
Reaction score
0
Location
Monroe, Oregon
I've yet to try the Epoxy Fixit available through Apogee. I've seen fillets done using this and they look great!
I tried using the Fixit epoxy and found it to be too stiff for getting smooth fillets. When mixed it's more like clay than a caulk. Once cured it's very hard (like granite) making sanding difficult as well. Needless to say my fillets using this technique are strong but visually imperfect.

I didn't try thinning it which may improve it's working characteristics but doing so may degrade it's strength once cured. Furthermore, I wasn't sure what to use as a thinning agent. Their website (http://www.avesstudio.com/Products/Fixit/fixit.html) sells a thinning agent which I may purchase at some later date.

It has it's uses and it will certainly stay in my build box but I'd prefer something with a lower viscosity.
 

Trident

Retired, plenty of kits
Joined
Jan 18, 2009
Messages
861
Reaction score
9
If you are doing white glue fillets:
Lay the glue in the fin / body tube joint - slowly. This will help keep air out of the joint.
Keep an eye on the fillet as it dries. Air bubbles will not show up when the white glue is first laid down. You can pop the bubbles when the glue is fairly wet. Use a toothpick, the wood tip will pop the bubble easier than trying to use the tip of your hobby knife.
If the glue is still very wet, it should flow in and fill the hole. If it doesn't, I'd wait until it's completely dry to lay in more glue. You can't add more glue on a half-dried fillet and smooth it out with a finger. Let the first fillet dry, then go again. I typically do three fillet layers.
Be warned, anytime you fillet a launch lug you are bound to get bubbles. That tight angle is nearly impossible to fill without bubbles.
I've yet to try the Epoxy Fixit available through Apogee. I've seen fillets done using this and they look great!
You can avoid all this if you use Titebond Trim and Molding Glue -- no bubbles.

http://www.titebond.com/ProductLineTB.asp?prodcat=5&prodline=4

Read the Product Features on this page -- it really is great for filling gaps and small cracks, which lends itself to fillets. While it says it is sandable, I have not tried this, but heard others state that it is.
 

luke strawwalker

Well-Known Member
Joined
Jan 18, 2009
Messages
9,147
Reaction score
16
You can avoid all this if you use Titebond Trim and Molding Glue -- no bubbles.

http://www.titebond.com/ProductLineTB.asp?prodcat=5&prodline=4

Read the Product Features on this page -- it really is great for filling gaps and small cracks, which lends itself to fillets. While it says it is sandable, I have not tried this, but heard others state that it is.
Second that... great stuff. It's very thick and stays put very well, but smoothing it is kind of a chore, because it would rather stick to you than to the rocket, but it's all a matter of technique I've found. Also, being a water solvent glue, I've found I can leave the fillets 'humped up' (convex) and they'll dry 'concave'.

It requires a little learning curve, but I REALLY like the stuff-- very little shrink, very smooth, and stays put... OL JR :)
 
Top