New Way Blade Runner, Part 12, Gluing On The Fins

The fins were painted before gluing on the blade fins.

The paint increased the thickness slightly. 

For an easier fit, the tab edges were sanded.

The blades were pressed in place. The fit was tight.

CA glue was set on the outside to lock the blades in  place.   

The tabs were sanded even with the faces of the blades.

Use a sanding block of this.

On the left - The tabs have been sanded even. The blades are flat.

On the right - Some CWF was brushed on, only on the outside flat face. This will fill any gaps and grain on the tabs and slots.

New Way Letter - Go Build, Part 8, Sanding the CWF & Filler/Primer

Here's the tube fill after working the CWF into the seams.

I usually hit the filler with 400 grit on a sanding block to start.

Take a close look at the end of the launch lug. That edge is rough and needs same sanding with 400 grit on a block.

On the left, there is already sanded CWF filler in the lug.

After sanding the ends clean, use a sharpened dowel to round the lug and clean up the inside wall. 

Thin strips of masking tape kept the filler primer of the root edge gluing areas.

On the right is the tube after sanding the filler/primer and pulling of the masking tape strips.

New Way Letter - Go Build, Part 7, Tube Seam Fill

I like to mark the tube spiral indents with a sharp pencil. It makes them easier to see when applying the CWF filler.

I dip just the tip of my X-Acto knife in the thinned CWF filler.

You won't need much, so wipe the excess off the back of the knife tip.

Run the tip into the seam recess with a back and forth motion. The blade directs the filler into the seam.

I dip and fill about one inch at a time.

I had hoped the plywood fins would only require some filler/primer to fill the very shallow grain.

There were a few "splinters" that needed some CWF and sanding.

Estes Black Star Voyager Build, Part 29, Filling The Fin Halves Joint

The joint got a coat of CWF and sanding.

Notice you can't see the U support piece, it's hidden inside the joint.

I wrapped a paper towel around the vanes previously painted with the metallic black.

I carefully sprayed some filler primer only on the joint.

After that dried, it was sanded with 400 grit on a block.

I was concerned about any misalignment of the joint but after sanding, the fit was good.

A glue fillet was applied to lock the U brace piece in place.

Semroc Wac Corporal Build, Part 8, Second Coat Of Primer/Filler

Normally, one coat of CWF then sanding - 

and a spray of primer/filler and sanding,

takes care of the balsa grain. Not today.

Before sanding the filler/primer I had to rub some CWF into the remaining visible grain.

Keep this CWF rubbed in filler thin and close to he surface.

After sanding down the filler/primer, you could see the remaining high spots left from the initial fin shaping. I wanted the surface to have a nice, rounded profile.

Sanding did take down the raised areas but also cut int the CWF underneath and into the balsa.

This will need another sealing shot of filler/primer and sanding.

The root edge was masked off again using tapered pieces of masking tape.

Onto some scrap cardboard to spray one side.

That long masking tape strip has the sticky side facing up to hold the fins for spraying.

Spray one side and let dry.

flip over the fins and spray the other side.

Estes Condor #0807 Build, Part 10, Balsa Filler/Primer

After one pass with CWF and sanding, 

the die-cut balsa still showed some crushed edges. I had to go back for more filler.

The balsa was sheet was pretty good. 

Here's a fin right after a shot of filler/primer. You can't see and grain pores.

Here's the tip fins with sprayed filler/primer - 

And a fin after sanding off most of the filler/primer.

The die-cut balsa tip fins have a rounded outside corner.

The instructions show a sharp corner.

Fillers Results, Part 2

The final results were somewhat predictable with a few surprises.

After light sanding the "fillers" all pieces got a white undercoat and light sanding. This was followed up by gloss red enamel.

   

On the left is the sprayed raw balsa, no sealer or filler.

The paint soaked in and dried with a dull flat finish. The balsa grain is very obvious.

On the right is the wood glue coat balsa. 

The grain is still evident, not filled. But - 

The wood glue did "seal" the wood. The paint didn't soak into the wood and dried to a decent gloss sheen. 

On the left side is the CWF filled balsa. There is still some grain and the pores are raised slightly. The final gloss is not as shiny as the wood glue test piece above.

On the right is the piece hit with filler/primer only. There is still some slight grain seen. The filler/primer does seal the wood and the gloss red is a little shinier than the wood glue coated piece.

 

The clear winner is this final piece using one coat of CWF and sanding, followed by filler/primer and sanding. 

The CWF fills 80% of the wood grain. A single follow up spraying of filler/primer and sanding fills any remaining grain.

This test piece is the smoothest with the best gloss.

This is how I normally fill balsa pieces. It's a simple two step process. One brushed coat of CWF and sanding, one spray of filler/primer and sanding.  

Everyone has their own methods, do what works for you. I doubt I will change, I've used and developed my practice of CWF and F/P for years now.

Fillers Results, Part 1

On occasion I see a forum post where a newbie recommends his method for filling balsa.

Some use white or wood glue claiming it fills the balsa. Others have used the Brodak sanding sealers.

In the late 1960s Estes recommended Sanding Sealer. Centuri said to use Balsa Fillercoat. I used sanding sealer and occasionally balsa fillercoat. You can't find sanding sealer in hobby shops anymore. If you do find it, the cost seems prohibitive. Pactra and Midwest has discontinued their sanding sealers and balsa fillercoats. Brodak sealer seems to be out of production.

I've read about CA )Super Glues being used to seal and fill balsa grain. I've yet to use CA for this. I tend to fill the balsa wood grain off the model. A CA fill would seal the root edges preventing wood glue from soaking into the balsa, compromising the glue bond.

When I got back into the hobby in 2009, sanding sealer was difficult to find. Elmer's Fill N' Finish (now named Carpenter's Wood Filler or CWF) was the talk of the forums. I adopted this filler on my rocket builds. 

In these two posts I took some scrap balsa and tried various methods to seal and fill balsa grain. This is not a complete test, I've not included the Brodak, Erockets sealer or CA methods. Papering fins is a discussion for another day. 

     

Five pieces of balsa were tested. I tried to pick out wood pieces that had some consistent density and grain depth. After filling, all pieces will get white undercoats and a final red color.

The first piece (not shown here) will be raw balsa, no filler. 

The second piece (not shown here) got a coat of wood glue and light sanding.

Third piece was raw balsa piece that only got one spray of Duplicolor Filler/Primer. After it dried it got a light sanding with 400 grit.

The fourth piece (not shown here) got one coat of brushed, thinned CWF and sanding.

This fifth balsa piece got a coat of thinned CWF and sanding.

This was followed by a spray of filler/primer and sanding.

Estes Great Goblin, #9724 Build, Part 7, Rounding Fins

This was a bit confusing.

There is an arrow pointing to and saying to round the leading edges of the fin. Leading edges? There's only one leading edge. The back is the trailing edge. 

The root and outside edges have a dashed line. Sand edges even. I assume that means to sand them square.

The old BT-55 based Goblin kit has you round the leading and trailing edges. That's what I'm going to do.

The forward fin shows the brushed on coat of CWF.

The fin in the back has the CWF sanded smooth. The pencil lines show where I need to apply more CWF and re-sand. 

Ideally, you should have left a thin skin of CWF after sanding. The pencil outlined areas were sanded down to the bare balsa.

TIP: To reduce saw dust -  

I sand in my lap, over on old dish towel. 

As I go I wipe the fin and sandpaper block off onto the towel. This traps most of the saw dust until I can shake it off outside.

Estes Blue Origin New Shepard Build, Part 5, Tunnel, launch Lug & Fins Fill

The leading, trailing and outside edges of the fins are slightly rounded.

The sides of the fins are not flat, but slightly curved! Don't sand the edges flat with a block.

The launch lug gets a standoff to clear the wide nose cone.

All the balsa pieces got a coat of CWF and sanding.

After that, all balsa got a shot of filler/primer and sanding.

Here's the tunnels with the low ends glued on. These are hanging over the edge of the scrap cardboard for spraying.

All the pieces were sanded with 400 grit to remove most of the filler/primer, filling any remaining balsa grain.

Estes Space Shuttle Columbia Build #1385, Part 7, Balsa, Launch Lug & Tube Filler/Primer

 

Here's the wing, rudder and launch lug ready for a good shot of filler/primer. The parts will be taped to a piece of scrap cardboard for spraying with loops of masking tape, sticky side out.

Spray one side, let dry.

Flip over, re-tape and shoot the other side. Be sure to get the filler primer on the outside edges.

The primer was sanded with 400 grit until the CWF just starts to show under the gray primer.

Down the center is the glue area to attach to the main body tube. I wrapped some 400 grit around a small glue bottle to remove the gray primer. 

Sand down to the the CWF filler. The CWF is water soluble and wood glue will give a good bond.

The body tube was also shot with filler/primer. 

The tube ends were masked off. 

I press and lift the tape against my pants leg a few times to reduce the stickiness. Sometimes you can start an interior peel of the tube when pulling off the tape. With the tape less sticky there is less chance of peeling and delamination.

Estes Space Twister #7258, Part 6, Primer & Fin Gluing

With the engine mount glued in,

The body tube got a shot of filler/primer and sanding to surface. The three fin position lines were scraped for a stronger root edge glue bond.

The picture on the right shows the fins glued in place.

Fillets were interesting - it's hard to smooth out a fillet on the inside top under the spin tab.

Look close and you can still see some balsa grain after the first shot of gloss white. There is also some roughness where the spin tab is glued on. 

I rubbed some CWF filler into the balsa pores. If you do this after spaying paint, used very little  filler and remove as much of the filler as you can. Sanding filler this late in the game - the filler dries harder than the balsa. You don't want to be re-sanding more than you have to. Sometimes the filler are will show after the final paint is dried. 

Here's the model after light sanding, ready for the second coat of gloss white. 

Estes Twin Factor #7250, Build, Part 9, Engine Blocks & Launch Lugs

The instructions show the two yellow spacing tubes taped together. They are pictured pushing the lower engine block in place.

I simply glued the lower engine block in the bottom, even with the end of the BT-5 tube without using the yellow tubes..

With the lower engine block glued into the bottom of the booster stage - 

Slide in the two taped together yellow spacer tubes into the booster stage. Slide the upper stage body down on the top half of the taped yellow tubes. 

The upper engine block is slid down from the top until it butts up against the yellow spacer tube. I applied a glue fillet around the top joint.

Here's one of the short launch lugs glued into the root edge fin joint.

Both the top and bottom lugs are glued towards the top leading edge of the adjacent fin.

Here's a step that isn't really needed, but I did it anyway hoping for a smoother final finish.

Some CWF filler was directed into the joint seams with the tip of a dull knife blade. After it dried, the bottom was sanded with 400 grit.

One shot of filler/primer and sanding followed, filling any remaining seams.

Estes Asteroid Hunter #3224 Build, Part 18, More Fills & Launch Lug Alignment

After fitting the Q piece back, the front end needed filling. 

More CWF and sanding!

Here's one of the two front launch lugs.

I traced around them and scraped away the paint before gluing the lugs in place with Fabri-Tac glue.

The rear lugs were also traced and the paint scraped off inside the pencil outline.

These were also glued on with Fabri-Tac.

Notice the tab that overlaps the back. 

Before the glue sets, double check the alignment of the front and rear lugs with a launch rod.

This design has guns that slip into the front lug holes when the model is on display.

Look close at the fillet areas on the sides of the Q pieces.

These took two passes of white spray and sanding after the paint dried.

Estes Laser Lance #3218, Part 2, Engine Mount

The engine mount assembly is standard.

Notice the green centering rings. Most of the green wrap was sanded off for a better fit in the BT-55 main airframe tube.

A rounded top dowel was used to put a line of glue inside the tube at the height of the upper ring. Note the dowel is set at the upper centering ring and marked at the bottom. The pencil line at the bottom represents the low end of the BT-55. The low ring will end up even with the bottom of the tube.  

The picture above on the right side shows a line a glue around the top of the rounded dowel.

The dowel is set in the tube up to the pencil line. Roll the glue around the inside tube making a glue bead.

Slide in the mount, not quite into the glue bead. Apply some glue around the top edge of the lower ring. Slide in the mount, even with the tube end.

Here I'm pressing the mount in using the flat face of my sanding block so the low ring and tube edge are even.

Some CWF filler was brushed around the flat end and sanded smooth. If all goes well there won't be any seam edge after the filler/primer coat later on.