Work on the lift for the Projection drawing table

Work on the Projection Drawing Table, the lift
Some fight today on how the lift should be designed. This lift, a sliding platform supports the slide projector. So it should be able to move it up and down with a fluent motion, no sticking, no shocks, no chance for the projector to fall off.
Three options:
1 Two sets gliders, top and down. The lift is a sledge-like construction, that has to carry the projector. It has gliders that got a sheet metal (tin) cover. This cover made it possible to slide over obstructions, such as the clamping strips and roughness in the boards.
The big problem is the reinforcement of braking. This is caused by the balance in their mutual points of contacts between pressure in the guide and the weight of the sledge carrying the projector. Blocking occurs if friction can not be reduced by rolling or smoother materials. As this was the case, I stopped further development of this option.
2 Two sets of rollers, one set up and one set down. This functioned perfectly. However it was a hell of a job to construct it and to line out the rollers. I have folded and nailed little bits of sheet metal strips on the wooded sledge. I got the feeling that this constuction should not become as complicated as this. So over to option three.
3 A sheet metal cover up and rollers down. "Up" has space restrictions. Anything attached has to pass the hinge between the fore and the behind legs of the table stand. "Down" has ample space, as it is at the front. Plenty space as well in width as in height, eventually to be translated in diameter of the rollers. Technically complicated it the relation between friction, the leverage of the load on the sledge, and the pull of the cords of the lift. However there is more. The construction has to defey these complications and be clear and a guide for understanding of how the system works.
Now at the end of the day, the choise is for three. Tomorrow this option should be worked out and tested.