No Duck Mo (“NDM”) - Part 2, Height Adjustment

In my mind’s eye I was looking at a lift bridge, hinged at one end and free to lift at the other. The hinge side would sit atop a height-adjustable tower as would the open-close side. These towers would need to be sufficiently far apart to allow easy passage of portly adults. The height adjustment characteristic had to be solved first because without that the NDM would be useless.

I used four ball-bearing drawer slides that are commonly found in office furniture such as filing cabinets and desk drawers. These operate very smoothly, have no lateral play, are available in several lengths and are quite easy to find at home centres (I purchased mine from The Home Depot).

one vertical tower showing the drawer slides partially extended

the vertical towers; colour coding is to facilitate setup and packing so I know which piece goes where

Two drawer slides are mounted on either side of each of the two towers. The lower portion of each tower consists of two 2x3’s glued together to make a nominal 4x3 (while dimensional lumber is sold in dimensions that are up to 25% in error – a 2x3 actually measures 1.5x2.5 inches, I shall refer to the nominal amounts when referring to dimensional lumber). These fit snugly into a pocket affixed to the base and are held in place by a 5-inch long bolt which passes through the pocket and the bottom of each tower (no nut is needed to keep these bolts in place). The bolts are also used to fasten the top of the “coffin” used to transport the NDM. 

The vertical towers inserted into the base; additional information about the base will be contained in Part 3

The top movable  portion of each tower also consists of two 2x3’s glued together to make a nominal 4x3. The drawer slides are attached to the sides of the nominal 4x3 pieces, allowing for the free vertical adjustment of each tower.

One large closed hook is fastened on the upper portion of each tower, to which is attached one end of a large turnbuckle. The lower end of the turnbuckle is fastened to the lower portion of the tower. The turnbuckles I purchased have a lock nut at each end, helpful but not mandatory. I purchased these from Princess Auto.

There are additional, smaller turnbuckles that pass between two hooks mounted to the end of the base and to the tower. The purpose of these turnbuckles is to make fine adjustments to the inward-outward position of the towers so that the bridge is positioned with perfect clearance from end to end – too sloppy and there will be a “pothole” in the track, too snug and the bridge won’t close all the way. These turnbuckles are adjusted as part of the final setup.

The lower end of the turnbuckle is positioned in an open hook located at the base of each tower – the turnbuckle needs to be able to be removed from the bottom hook for transporting.

To be continued...