Fairing Model: Tool Assembly
Dateline: 04/21/99At this point, the bulkheads and foam are cut. It's now time to start assembling the tool on the shaft.
Bulkhead Assembly
The tool was designed to be mounted on the filament winder. We expected construction to take several weeks, though, and we didn't want to tie up the equipment for that long.
During the assembly stage, we placed the shaft between two ladders. We also hung a lifting strap from the overhead crane to the center of the shaft. This was in part so we could easily move the tool during assembly, but it also helped remove some sag.
The sag at this point should have told us the shaft wouldn't be stiff enough. We thought, however, that the foam and bulkheads would stiffen things up. That turned out to be a bad assumption, but I'm getting a bit ahead of the story.
Starting the assembly was simple. We measured the bulkhead locations on the shaft, then slid them into place. To hold them where they belonged, we tapped some holes and screwed some blocks to either side of each bulkhead.
With all of the bulkheads in place, the tool was starting to take shape.
The part is supposed to be made as one piece. Rather than removing the part, the tool would simply be disassembled. To get the bulkheads out, the placement blocks would have to be removed.
To get access to the bolts, we cut fairly large holes in the bulkheads, similar to vent holes in a standard oven or autoclave tool.
The central portions of the bulkheads are also segmented, held together by screws in the outer bulkheads (one of those screws is visible at about 10 o'clock on the foremost bulkhead). Disassembling the bulkheads would make it much easier to remove them from the inside of the part.
Installing Foam
The foam blocks were all cut to size. They fit between the bulkheads without any trimming, and we temporarily used packing tape to hold the blocks in place.
The blocks were held to each other and the bulkheads with an adhesive. We tried several different materials before finally settling on Liquid Nails. Epoxies were too thin and soaked into the foam. Some quick-drying materials wouldn't bond to the foam. The Liquid Nails set pretty quickly and provided a pretty good bond.
Once the Liquid Nails had set, the packing tape was removed. There were some small gaps left where an integral number of blocks wasn't quite enough. In those cases, we hand trimmed some pieces to fill in the spaces.
In the end, we were ready to install the foam between the central bulkheads. The plan was to install all but one or two pieces, leaving room for the strap. The tool would then be moved to the winder (using the overhead crane), the strap removed, and the last pieces of foam installed.
We actually got as far as installing the foam before we realized the tool still had too much sag. Having all of the foam in place did remove some sag, but not enough. Because it did improve the situation somewhat, I thought that rigid internal bracing would solve the problem.
Next article, I'll show how we installed the braces.