All cats like boxes - this one they will love!
This is a DIY project for your IKEA KALLAX shelve.
And of course for your cat.
Besides a 3d printer you will need a fitting box like DRÖNA or any other box with a size of about 33x33x33 cm.
Print both STL files (Ring01 and Ring02).
You need to cut a hole into the box with a diameter of 16 cm.
If you use a box like DRÖNA with paperboard inside you can just cut out your circle with a sharp knive. It doesn't have to be perfect, the ring will cover most mistakes.
Take Ring01 and put it behind the hole, the bars have to be all guided through the hole.
Place Ring02 on top of it from the other side.
Make sure that the slots are lying on top of the bars and press them together.
The rings should fit and hold together without any adhesion. If neccesary glue them together with a little superglue.