You should get the details about caring for the Shinai from your trainer. Before using a newly purchased Shinai, after removing the colored package twine, it is important to dissemble the Shinai, to sand the inner edges with a fine grade sand paper and to lightly lubricate the individual bamboo strands with a clean, clear oil.
The inner side especially absorbs the oil and thus prevents the dry bamboo from breaking. For safety purposes, it is important in reassembling the Shinai to pay special attention to the correct placement of the parts.
It is especially important that the band (Tsuru) is tightly stretched so that the tip of the Shinai (Kensen/Kissaki) does not come off. From time to time the Shinai should be assembled, changing the "cutting side" so that, in the course of time, all four bamboo strands are subject to equal strain. .
Before every training session make sure that the Shinai has not been damaged and that it is in good condition.