Going to give CWF another try

[MichaelRapp]

When I last was working on a rocket (late February, it's been an unusual last few months, obviously), I swore I would never touch CWF again. I've always just had such problems with it. I abandoned it and switched to papering fins using Avery labels, which worked well, until I realized that they are easy for simple swept parallelogram shapes, but get trickier with more complex fin shapes.

I want to give CWF another try. In the small areas of fins in which I've done it well I do get that lovely plastic look after priming and painting. I've been doing some reading and video watching, and I think I know where I've been going a little bit wrong with CWF. My first problem is in my CWF to water ratio. I've been just eyeballing it, so my ratios change every time I make it. I stumbled upon Chris Michielssen's ratio of CWF to water of 2.5:1. I tried that tonight, and this is significantly thinner than what I've been using. It's still viscous, but it is not a paste either.

This leads me to my second problem. I've been putting this stuff on way-too-thick, almost like I was frosting a cake. CWF, of course, sands really easily, but I'd still have these (relatively) tall mountains I needed to sand down and in doing so I may have been getting too close to the balsa in other areas. In any case, I never seemed to be able to get it perfectly smooth and after I had primed and painted the rocket, these slight but visible shallow gouges were clearly visible.

So I've got a few balsa triangles I'm playing with tonight. I put on enough of a coat to cover the grain (and I didn't forget the edges, save the root edge), but not too thick.

I also switched my paintbrush. Historically, I've been using those 1" ultra-cheap disposable brushes you can get at Home Depot. I think the coarseness of the brush fibers were really causing me problems and creating some of those mountains and valleys. Tonight I'm using a 1/2"-wide artists brush with very smooth fibers and it is making a difference. It does seem to allow me to work the CWF into the wood without creating those ridges.

I'm going to let them dry overnight, sand tomorrow, and see how I did.

 

[Scott_650]

Don’t discount the effect primer can have - a “high fill” filler primer helps to provide a good base for the CWF. Good luck with your attempt.

 

[Ronz Rocketz]

https://www.amazon.com/Paint-Brushes-Acrylic-Detail-Painting/dp/B07ZJ6KC6H

 

[FredA]

WTF is CWF.

It's a dying courtesy to tell us what acronyms means.

 

[MichaelRapp]

WTF is CWF.

It's a dying courtesy to tell us what acronyms means.

Wild, when I was writing that I didn't even think that I hadn't expanded it at least once. I apologize..... Carpenter's Wood Filler. I specifically am using this one:

 

[o1d_dude]

When I apply CWF, the consistency is that of muddy, silty water which I’d guess is the 2.5:1 ratio Chris M recommends.

Might take a few applications to get good coverage.

Stir the mix frequently while working with it. NO lumps!

I let it dry overnight before trying to sand it.

I mix in small epoxy mixing cups and use wide blue tape to seal the moisture in for the next day’s work. Depending on the seal, I might add more water to get the right consistency.

 

[heada]

I mix it until thin peanut butter or mustard. I get it close and then add water dropwise. It's easy to add a bit more but a pain to wait for it to evaporate to thicken up.

I don't use it on fins, only to fill tube spirals. Papering balsa or basswood fins always gives me a better finish and a stronger fin.

 

[neil_w]

Nothing wrong with CWF but I would dispute the idea the complex fins are a problem with label papering, if you use the right technique.


Well that was a fun trip down memory lane.

 

[MichaelRapp]

Nothing wrong with CWF but I would dispute the idea the complex fins are a problem with label papering, if you use the right technique.
View attachment 436893 View attachment 436902 View attachment 436900 View attachment 436896
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Well that was a fun trip down memory lane.

My technique so far involves papering the leading edge; that is, always wrapping the Avery label around that edge, which makes trimming complex areas difficult. For some reason I've always thought papering the leading edge was important. I've never tried doing the two sides individually.

Do you use labels or glue to adhere yours?

 

[neil_w]

My technique so far involves papering the leading edge; that is, always wrapping the Avery label around that edge, which makes trimming complex areas difficult. For some reason I've always thought papering the leading edge was important. I've never tried doing the two sides individually.

Do you use labels or glue to adhere yours?

Label paper, usually. The first time I tried it I did indeed wrap around the leading edge, but had issues with that, and since then paper each side individually, and just make sure to glue-seal *all* the paper edges, eight with TB2 or thin CA.

Besides, wrapping around the leading edge only works with straight leading edges, and mine are often... not.

I'm hoping to make a video showing how I do it, but haven't gotten to it yet. In the meantime, here's a brief summary of my current technique, which is always evolving. Of course there are an endless number of perfectly valid different approaches that folks use; this is what works for me.
1) Sand each side of the fin with 400 or 800 grit paper to make it pretty smooth.
2) Brush off the dust with a soft paint brush, and then us blue tape to pull off whatever remaining dust is there. I don't know if the blue tape step is strictly necessary, but it definitely does remove some dust, and my theory is that *any* remaining dust can get in the way of a good long-term bond from the label paper.
3) Cut label piece slightly oversized in all directions except the root. I find something like 1/4-1/2 inch slop works well.
4) Apply label to one side of fin. Stay very slightly off the root edge, so you can just see a bit of wood showing there. That seam will eventually be covered by a fillet.
5) Sand off the excess on each edge using a 400 grit paper. Most recently I've been using a sanding stick I made with some 1/8" dowel, which works really well and can maneuver curves easily. Make diagonal strokes from the fin towards the edges, moving along the edges with each stroke (If you go back and forth on one spot, you're likely to go through the paper too quickly and start sanding the fin edge, which you don't want to do). If possible stop before you sand all the way through; once you get close you can just pull off the excess piece. Then finish up with 800 grit paper until it's clean. 800 grit paper will generally not damage the labels.
6) Repeat other side.
7) Apply glue (nowadays I'm using thin CA, but you can do it with TB2 as well) along each edge of the paper (NOT the root edge), as well as the full exposed edge of the fin.
8) Sand edges smooth with 800 grit paper.

Seems like a lot of steps but it goes *extremely* quickly, no opportunity for warpage, and the only step where you have to stop and wait for anything to dry is step 7. Steps 1-6 typically take me only a few minutes per fin, a bit more if it's a complex shape.

These instructions really needs some pictures, but I can't provide any at the moment. Will make that video one of these days, or may do a really well-illustrated thread. Good winter project for me.

Final notes:
1) if you do a sanded primer coat, you *must* not sand all the way through the primer or you will damage the surface of the paper (unless you use 800 grit paper, which is a hell of a slow way to sand a primer coat).
2) Square fin edges are easiest, but round edges work fine as well, just need to go a little more slowly and carefully.

 

[hcmbanjo]

Hi Michael,

Here's some blog articles about CWf coverage, warping and a comparison to another fill technique by John Boren.
https://modelrocketbuilding.blogspot.com/2012/06/semroc-goblin-build-part-6-fin-grain.htmlhttps://modelrocketbuilding.blogspot.com/2019/11/cwf-wood-filler-warp.htmlhttps://modelrocketbuilding.blogspot.com/2017/08/john-boren-build-prep-article-in-apogee.html
On Papering fins -
If a leading edge is rounded, I'll roll the paper over the leading edge.
Here's a post from a Halloween build and a Flutterby:
https://modelrocketbuilding.blogspot.com/2019/10/bones-halloween-build-part-6-fin-skins.htmlhttps://modelrocketbuilding.blogspot.com/2013/12/centuri-flutter-by-build-part-5-paper.html
I've got nothing against sanding sealer or papering fins. I simply prefer a two step process
of CWF and sanding, then a coat of Duplicolor Filler/Primer (FP101) and sanding.

I'll use 220 grit on a block to remove most of the rough CWF, then smooth sand with 400 grit,
trying to leave a "skin" of beige CWF on the fin. If I see pink raw wood, I do another pass with the CWF.

 

[neil_w]

What I've found is that, for whatever reason, I really *enjoy* the process of label papering, whereas I don't particularly enjoy working with CWF (although I still use it for spiral-filling). Excellent results can be achieved either way.

 

[Jeff Lassahn]

I print or draw my fin outlines on paper, paper a sheet of balsa before cutting (using the printed template on one side and blank on the other) then cut everything out,
It's really convenient, but leaves you with square edged fins with no paper on the edges.
If the paper is well glued, You can sand through the paper to round the edges, then finish just the leading and trailing edges with wood filler. I'm using CWF that's just barely thinned down, much thicker than described above, but since I'm only doing the edges the total extra stuff to be sanded isn't very much.

 

[MichaelRapp]

Thanks Neil and Chris for your suggestions and help. I also want to give papering fins another try, as well.

This stuff is difficult to photograph, but here is a before photo of my test balsa triangle:



I sanded with 220, then finished up with just a few swirls of 400. Here's what I ended up with. I still has some slight high spots and did get down to the balsa is just a few very small areas, but I think primer will fix these. (I'll find out in a bit!)



I think this is the best result I've ever gotten.

 

[jrap330]

Nothing wrong with CWF but I would dispute the idea the complex fins are a problem with label papering, if you use the right technique.
View attachment 436893 View attachment 436902 View attachment 436900 View attachment 436896
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Well that was a fun trip down memory lane.

Wow..with all those advance curves some leaving little fin area, you must be determined to even try...great work Neil.

 

[MichaelRapp]

Neil, have you ever had any issues with the label paper peeling up, perhaps in the center where it isn't sealed by CA and causing a bubble in the paint?

 

[neil_w]

Neil, have you ever had any issues with the label paper peeling up, perhaps in the center where it isn't sealed by CA and causing a bubble in the paint?

Never. The papered fins in my fleet range from 0-5 years old, zero bubbles or peels so far. I don't know if they'll eventually deteriorate over some number of years, but so far so good. I would hope that they are sufficiently well sealed off from the air by the paint that they'll remain stable.

 

[MichaelRapp]

And here's my first try with papering the fins on both sides. It went well. I'm a little out-of-practice with thin CA, apparently, as I put on a bit much. I forgot this stuff paints itself; no need to squeeze the bottle. I did not realize how easily CA sands down with 800 grit. It's nearly smooth now, except for some very slight bumps where the biggest CA globs ended up.

Prior to CA, and just after burnishing the edges with 400:



After CA and 800 sanding:

 

[o1d_dude]

Neil, have you ever had any issues with the label paper peeling up, perhaps in the center where it isn't sealed by CA and causing a bubble in the paint?

Yes.

Particularly on hot days, the labeled fins “inflate“.

Highly annoying and I’ve not labeled or papered fins since then.

Locally we fly on rough terrain...none of those mythical putting greens I see in some forum members photos and videos. For us, it’s rock outcroppings, creeks (mostly dry with river rock beds but occasionally water filled), disked fields good for ankle sprains, fence posts, and dry oak trees.

With fields like these, the most perfectly finished rocket remains pristine only till the first landing.

California is NOT a rocket-friendly state and setting up in a local park or school athletic field is recipe for a police interview at best, tickets and fines at worst.

Fiberglass rockets and rough terrain on private property is our lot.

 

[neil_w]

Just for curiosity, I timed myself papering this fin:

All straight edges, leading edge is rounded, so pretty easy. Took me just over 6 minutes, both sides finished except I didn't apply CA to the edges and sand (which I was too lazy to do since this isn't an actual fin for a real rocket). Is that quick? I don't know, maybe not. Quick enough for me, though, and enjoyable, with good results and no mess.

 

[Bill Heath]

Press your label papered fins between two flat smooth surfaces(boards) for 24 hours. The adhesive is pressure sensitive. Believe me, it works.

 

[MichaelRapp]

Press your label papered fins between two flat smooth surfaces(boards) for 24 hours. The adhesive is pressure sensitive. Believe me, it works.

That's an excellent idea!

 

[MichaelRapp]

I did some priming yesterday. (And realized I am really out-of-practice with many things in model rocketry. I didn't have much experience to begin with -- just six rockets so far -- but I have forgotten so much over the last nine months!)

While I did just a light coat of Duplicolor FP101 primer on the CWF'ed "fin," it came out pretty good! The grain is just barely visible. A sand, plus a thicker coat would probably work well. And no gouges! My take-away is to remember that I am applying CWF to balsa, not frosting a cake. (Yes, I skipped the edges for some reason.)

Here is a question I have: should I continue to prime and sand until the grain is invisible, or would this be could enough to start painting?



Here is my test of my fin papering. Here I sort of remembered how I used to prime. I did three quick sprays on each side, then waited a few moments for the shine to disappear and repeated a few times.

Of course, the big deficiency is that you can still clearly see where I over-CA'ed the edge, and I thought I had sanded these down quite well. Obviously not! I need to practice a bit more with that.

I do like how FP101 applies so smoothly. It only takes a bit of 400 to get it very, very smooth (not done yet in the below photo).

 

[neil_w]

Here is a question I have: should I continue to prime and sand until the grain is invisible, or would this be could enough to start painting?

If the grain is visible now, it'll be visible after painting. It's up to you. I will say that you could definitely do more sanding on that fin, there's still a lot of primer on there. That could reduce the grain somewhat.

Of course, the big deficiency is that you can still clearly see where I over-CA'ed the edge, and I thought I had sanded these down quite well. Obviously not! I need to practice a bit more with that.

If the areas that look like drips are CA and not just primer drips, then it appears you used something other than thin CA. Thin CA would not build up like that (although it still requires sanding of course).

I find build-up of CA on balsa to be very difficult to ever sand smooth, since it's so much harder than the surrounding material.

 

[MichaelRapp]

If the areas that look like drips are CA and not just primer drips, then it appears you used something other than thin CA. Thin CA would not build up like that (although it still requires sanding of course).

I'm using the typical Bob Smith Industries Super Thin CA. Now with that said, I didn't use a tiny applicator tip, and I did squeeze it on a bit heavily as I forgot this stuff "paints itself". Also, this bottle is perhaps 18 months old now. (Stored at room temperature.) I wonder if it has degraded.

 

[Spitfire222]

One thing I didn't see mentioned is the use of sanding blocks to help avoid gouges. You can never have too many sanding blocks and grits of sandpaper. You might consider buying sandpaper in bulk and throwing away often (i.e. don't try to stretch the life of your sandpaper; if it gets clogged or used up just replace, or you risk hurting the finish you're trying to achieve). With that being said, you can still gouge your work with a sanding block, but you can minimize this by going slowly and checking your work often. Starting with an even application of CWF helps, but you should be able to salvage on uneven coat with careful use of a sanding block.

With regards to the finish, it's totally up to you how much effort you want to put into it. Some people don't smooth over fins at all (the horror!). Personally, if I'm going through the effort of primer and CWF at all, I want to eliminate the grain completely. I agree with Neil that the test piece could stand more sanding. Ideally, you want to remove almost all of the CWF and primer so that it only fills the grain holes/pits. It's not uncommon for my fins to be exposed balsa with streaks of tan and/grey from the CWF/primer, and you'll be surprised how smooth they are despite how mottled they look. You arrive slowly and carefully to that finish by progressing from coarse sandpaper (heavy material removal) to fine sandpaper ("polishing"). Good luck, it doesn't have to be complicated.

 

[neil_w]

I'm using the typical Bob Smith Industries Super Thin CA. Now with that said, I didn't use a tiny applicator tip, and I did squeeze it on a bit heavily as I forgot this stuff "paints itself". Also, this bottle is perhaps 18 months old now. (Stored at room temperature.) I wonder if it has degraded.

I apply with a Q-tip, rather than glopping it on. With SuperGold, it will last just long enough for me to hit the edges before it hardens up on the Qtip. With the InstaCure there might not be time, although in my experience an 18 month-old bottle will cure a little slower, which will work to your advantage.

In any case, you want just enough to penetrate the edge of the paper and the wood. If it pools up... well you end up with that, and you'll have a tough time getting that smooth. Definitely use your fingers to test (after it's fully cured! ); you should be able to feel those bumps before you start priming.

 

[BDB]

Has anyone bought any CWF lately? I noticed a few weeks ago that my local Lowes doesn't carry it anymore. They had several different kinds of Minwax stuff that looked like this:


I ended up buying a tube of the color-matched Minwax wood filler because I actually needed it to fill some cracks in some poplar trim that I was installing in my house. It worked pretty well for that, but I have no idea if it's a good CWF alternative for rocketry.

 

[neil_w]

Elmer's CWF availability seems to vary over time. Amazon has it. I have taken a liking to the small 4 oz tubs (https://smile.amazon.com/Elmers-Products-Carpenters-Interior-Filler/dp/B000H5OQIU/). The lid seals securely, and I just pre-thin the whole thing for my desired use. Pop the top, dip and go.

I also have a little tub of the DAP color-changing formula (https://smile.amazon.com/DAP-540-Natural-Plastic-Wood-X/dp/B01IY7RGBQ/) which seems to perform similarly but has a bit of an odor that I'm not crazy about, vs. the almost 100% odor-free Elmer's.

 

[cbwho]

What does CA stand for? Construction Adhesive??

I don't know what others do, but in the late 80s, the truck I did was to coat the balsa fin with carpenters wood glue on what side, let it dry. It will curl but then put cwg on the other side, it will flatten. Lightly sand both sides and put in the leading and trailing edges with sand paper, then coat with cwg glue again, then lightly sand. After complete, spray paint, super smooth.

Have others tried this?