With the mechanisms operating (somewhat) smoothly, it’s time to mount the table top. The process is fairly straightforward: place the carcass on the top, align the two, trace the racks onto the top, then mortise them.
According to Helmuth von Moltke, a Prussian military strategist, “No battle plan survives contact with the enemy.” When your plan meets the real world, the real world wins. Nothing goes as planned. Errors pile up. Mistaken suppositions come back to bite you. The most brilliant plan loses touch with reality (Lexician).
The mechanisms, now installed in the carcass, are stiff. They don’t move freely which is a necessity. Otherwise, the table will bind and won’t open. I began the investigation by checking each rack/guide individually outside of the table to make sure it moves freely. Ideally, they should slide by gravity alone when held vertically although sometimes, they require a push. My first “discovery” during this process was that the drive barrel was making contact with the lower guide. It left a “rub ring” around the barrel very near the gear (as shown in the above photo), and a shiny spot on the lower guide brass. After a quick consultation with Jon the machinist, I addressed these areas with a file to relieve material, and while it did prevent further contact, it did not rectify the problem.Another thing to consider…
Even slight differences between the aprons and legs can be enough to cause the mechanics to “hang”. If the legs protrude even less than 1/32 inch out from the side apron the lower rack gets caught. I gently used a chisel with a swiping motion to bring the two surfaces flush. Depending on the severity, however, it still leaves marks.
My current thinking is that the rack is too closely fitted to the drive gear. That is, the rack and drive gear are so tightly positioned that it’s causing excessive friction in the mechanism. I’ll test this out by relocating the rack and guide slightly lower than it currently is, and report back.
While contemplating this issue a thought occurred. It would seem that the position of the lower racks/guides with relation to one another is not critical. In other words, they don’t really need to be aligned at identical heights in the aprons. So long as the main box is mounted squarely to them the height shouldn’t be a problem. We’ll soon see how this turns out.
Update (29 May): I adjusted the spacing between the drive gear and racks, in addition to relieving some “pinch points” in the guides, to get things moving. However, I think the change in temperature had the greatest effect on things.
Before we can proceed to shape the carcass, the mechanisms must be completely installed and operating properly. With the mechanisms in place, the challenge becomes mounting the main box and tabletop to them. The tabletop is relatively straightforward: center it on the carcass, then mark the top racks. The main box, however, isn’t so simple. Not only does it have to be located left/right, front/back within its opening, but it also needs to be situated in height above the carcass floor. If it’s too high, the bolt on the latch won’t catch; too low, and the bolt will drag on the main box as it opens. To complicate matters, it is impossible to directly mark any of these components. They’re buried deep in the carcass interior!
Being the case, I’ve devised the following plan…
While I’m certain some level of adjustment will be necessary, this methodology provides a plan to move forward. Such is the nature of product development or, to put it another way, if we knew what we were doing, it wouldn’t be called research!
The main box latch is the trigger for the table’s entire mechanical system. When the key is turned within the right side apron, it actuates a lever releasing a bolt from the bottom of the main box. Under the tension from the drive mechanisms, the main box is propelled forward while, simultaneously, the table top slides back. Before proceeding with the mechanisms, it’s necessary to mortise in the main box latch.
This is a bit of a delicate operation. The latch mechanism has a 90° bend where the key connects which has to be mortised behind the lower rack guide. It also has a sleeve into which the key is inserted. This needs to be contained within the apron, not protruding from it.
After a bit of drilling, sawing, and paring things finally slide neatly into place!
Next, the long portion of the mechanism must be mortised into the floor of the carcass.