Estes Saturn 1B, #7251 Build, Part 3, Tube Seam Fill

I'd recommend filling the tube seams before assembly. It is difficult to fill the seams after they are glued in place. The eight booster tubes end up too close together to reach the seams. With the vacu-form wraps attached it would be difficult to fill and sand the BT seams close to the wrap.

Always check the tube ends to see if the cuts are clean.

One side of the large tube was rough. It took a just a few passes with a sanding block to square up the end.

To fill the seams, the seams were marked with a thin mechanical pencil to see them easily.

I did my first fill pass using thinned CWF.

The tip of a dull blade was dipped about halfway in the thinned CWF. Wipe the backside of the blade off the rim of the container, the filler left on the back of the blade is probably more than you'll need.

The blade is dragged back and forth down the seam guiding the filler into the groove. Each dip of filler fills about 1" length of tube seam.

Here's the first three steps of seam filling - 

Left: The bare tube right out of the bag.

Middle: Tube seams marked with a fine mechanical pencil to see them easier.

Right: Thinned CWF filler applied into just the seams using the dull blade tip.

The inset picture shows the escape motor tube. It's a smaller tube, a little larger diameter than a launch lug. On a small tube like this, it's easier to brush on a coat of CWF then sand after it dries.

Build time:

Tube seam fills - 1 hour

Sand seam fills - 1 hour

Total build time so far: 2 hours, 30 minutes