i think if you sand it use a chisel it will'nt be so rough, but if you use a sand paper, please use the mid-soft one. and to clean it up just use toilet paper that the surface is enough rough but not to rough to clean the dust of the plastic or you may like to wash the entire cube. but i recommend you don't use jig a loo if you don't know how to lubricate the cube with special method, coz if you just spray it inside the cube it will harm the plastic and the cube rotation won't be smooth.