Hi, which second sentence?
Note: In answering your queries, the sketch in the original post is a simplification, it only shows the concept, which I wanted to know if it was an acceptable mechanism, which is seems it is. The details are in progress.
- That looks like an adjustable length simple beam to me ... IT IS A SIMPLE BEAM.
- What is it being used for ... SUPPORT A MOVING LOAD, ON CASTOR WHEELS, THERE WILL BE RAILS ABOVE TELESCOPIC ITEMS, AND OFFSET RAILS ON THE TELESCOPIC MEMBERS.
- how is it adjusted in length, what means or mechanism , how often is the length changed, how easy does this have to be? ... MANUALLY, OFFSITE, NOT VERY OFTEN, DOESN'T HAVE TO BE EASY. THE MAIN REASON FOR THE QUERY WAS TO SEE IF IT WAS A "DONE THING" OR AN ACCEPTABLE STRUCTURAL MECHANISM, WHICH IT SEEMS TO BE.
- What are the shapes, the make-up of these two beam sections, how do they nest? ... RECTANGULAR HOLLOW SECTIONS WITH PLATES OUTSIDE INNER MEMBER, AND INSIDE OUTER MEMBER. NOTE, OUTER MEMBER IS SHOWN AS SIMPLIFIED IN THE ORIGINAL POST, I DO HAVE SPACE TO WELD PLATES ON THE INSIDE.
- Fab and rolling tolerances vs. straightness for easy operation and nice running of the bearing points (pads) are always in competition ... THANKS FOR POINTING OUT, I WILL TAKE INTO ACCOUNT THIS AND THE DEFLECTION DUE TO GAPS WHEN FITTING, TO ACHIEVE A LEVEL RUNWAY.