As can reasonably be expected, various random events have intervened to cause further delays. There was a disconnect between what I thought I ordered for the oak slats and what I actually specified. That drove the need to step back and recalculate. We encountered several issues during our test rib build that have driven a minor structural redesign (more on that later). But, that's why we did the test!
Further, a dead refrigerator, a broken car windshield and a computer that won't display any video complicated efforts to move the TD forward. The windshield is being replaced as I type, the fridge service is tomorrow (hopefully it is repairable) and the computer, well, a new video card and a replacement power supply both failed to make a difference. The computer is an auxiliary one anyway, mostly used as a print server and to run SETI, so it can wait.
The Test Rib
In review, we decided to build a test half-rib from red oak that we cut ourselves, but later switched to building a full 8-ply rib from white oak that we sawed to 1/4" from an 8/4 board that was nominally 1-13/16" thick. The overall length of the full rib is 18', and we could not get an 18' board, so each ply had to have at least one joint.We cut and dry-fit the first four layers, then cut the other four without laying them into the mold. We decided to attempt two joints in one ply to maximize the utilization of the wood.
Given that we only have so many hands, that the open working time of the glue is critical, and that handling a bundle of glued and slippery boards 18' long into position in the mold seemed daunting (for good reason!), we decided to attempt only four plys on the first gluing, subsequently gluing up the other four and adding them to the first four.
But while we were applying the glue to the slats we realized that the time it was taking to spread the glue mandated that we put the first three plies into the mold before it was too late. A few days later we removed those first three from the mold and prepared for the next step. Here is a photo of the first three, positioned on the base trailer to give a sense of overall size and shape:
Next we added three more plys to the assembly, then finally the last two. Here are some photos showing the full eight plys in the mold:
- View at Rear (Hatch Area) -
- Clamping Station Detail -
- Shallow Portion of Curve -
Overall, we were very pleased with the 2x4 blocks screwed to the work table and the use of shims to clamp at each station. As you can see, we occasionally added a clamp between stations to pull the layers together.
Since the rib is wider than the target 1-1/2", we will flatten one side somewhat, then run the rib through the table saw in two passes (one for each side) gradually bringing it down to the 1-1/2" desired and evening out the sides.
Lessons Learned
The first lesson is that attempting to lay up a full rib with all eight plys just isn't workable; we don't have enough hands and glue working time.
The second learning is that it will be much easier to do the laminations if no joints are involved in any ply. As the bundle of slats is being positioned in the mold the layers have a tendency to slide relative to one another. Even one joint in each layer is challenging because you have to move one layer relative to two other layers without disturbing their joints. Since we cannot get 18' lumber, that means we have to build the ribs in two sections - front and rear. By bringing the sections together at a cross-member we will be able to retain structural integrity while vastly simplifying the lamination process. We will be able to glue up 8 slats no more than 10' long, get them into the mold and clamped without difficulty. While this doubles the number of laminations required, it will be achievable.
The next step is to calculate the longest possible rib section length that can be created from our milled stock, and determine if that length can work with the positioning of the partition that separates the cabin from the galley. If not, then we will position an oak cross-member at an optimal point in the curve to join the sections. More soon!
