I want to build a shelf that can I can place near a wall and still be able to rotate it around 180 degrees. I therefore would want to mount the shelf on a rotating pole and to reduce the needed distance to the wall would have a sliding mechanism that lets me slide the shelf off-center to one side (see the following sketch).

Sketch of the sliding mechanics

I built the following prototype out or cardboard to verify the idea.

Cardboard Prototype

So given I can get the center pole to be stable enough (for example by attaching it to the wall) is it feasible to have such a sliding mechanism that can hold a weight of around 40kg in the off-center position and still slide? Am I missing any other critical problems here? Any hints for similar existing parts or mechanisms would be greatly appreciated.

  • $\begingroup$ Neat prototypes! $\endgroup$ – KlaymenDK Feb 17 '20 at 14:11
  • $\begingroup$ Thanks :) it has been a lot fun making them. $\endgroup$ – Nicholas Feb 17 '20 at 15:54

Based on your nicely constructed model, it appears that two axes of movement will be required. The vertical axis can be addressed by a pair of bearing assemblies securely mounted to the top and bottom of the center pole:

bearing assembly

It may be necessary to find a different type of assembly which allows you to secure the inner race to the pole, but the image serves the purpose of this discussion.

I found this pillow block bearing which has a setscrew on the inner race:

pillow block assembly

These types of bearings are usually designed to tolerate axial loading but for light duty, slow speed operation will probably hold well enough. You may also find some other bearing types suited for thrust loads.

With a suitable bearing assembly on each end of the pole, one could create a trolley to attach to the bearing assembly. This trolley would ride in a track internal to the shelf structure.

roll-off track wheel

This image above is for a rolling roof mechanism. It would be necessary to have four of these at each bearing assembly (at the corners?) and matching rails above and below both bearings.

None of this is to scale and a 40 kg load may require large scale components.

I've been building a CNC router which uses v-shaped wheels, riding in aluminum extrusions with matching v-grooves. This permits the carriage to travel from one end of the gantry to the other, but it's not carrying 40 kg, either.

3D printers use linear bearings which provide similar movement, but again, not 40 kg loads.

The distance to the wall will be based on the spacing of the travel wheels from the axle center as well as the size of the wheels. I can envision using in-line skate wheels with matching tracks, providing suitable load capacity. One could get away without using the wheel portion and having bearing contact directly on the travel rails, if there is sufficient clearance.

  • $\begingroup$ Thanks for the hints. I will now research more about axial loading of these kind of bearings! $\endgroup$ – Nicholas Feb 17 '20 at 14:11

What you are looking for is already available as 70" TV mount, pull down over fireplace, in many Internet shopping sites for prices ranging between $50-100.

I add a photo just as an example.

enter image description here

  • $\begingroup$ This seems to solve a similar issue but with a different mechanism. I would really like the rotational way of hiding the TV $\endgroup$ – Nicholas Feb 17 '20 at 15:55

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