I have a Shtender and it has an option to remove the top part of it and use it as a table-top Shtender. Is doing this — removing the top part to use as a table top or putting it back to be used as a regular Shtender — allowed on Shabbos?Another aspect of the question is the height can be adjusted to make it a sitting or standing Shtender and is adjusted by using a screw like implement is one allowed to adjust the height (My concern is Boineh or Makeh Bpatish.)
Rivevos Ephraim 5:264 goes through this sugya,and brings opinions some which Gershon Gold already mentioned which allows adjustment on shabbas.However he brings a shittah which holds that a yeshiva shtender which is constantly adjusted is mutar,but a shtender which is used at a specific height should not be adjusted.see inside.
Rav Nissim Karelitz in Chut Shani (Shabbos 1:36) permits this based on the Chazon Ish (Orach Chaim 50:9) who permits screwing the lid of a baby bottle on, on Shabbos as the bottle is a Keli without a lid and one isn't changing anything by putting on the lid. The same applies, says the Chut Shani by a Shtender as it is usable without the top part.