How wide is your belt sander? The whole idea of a base grind is to make your base flat again. I think you will find it difficult making your base flat with a belt sander. Might be worth just taking it to the shop for a tune.
From our tuning shop article...
Base Grinding
During a full service, grinding the base is a very important step in getting your board to perform at its optimum. Snowboard bases should be flat. Poor performance is a result of base high base (convex) and edge high bases (concave). It is essential to get the base and the edge level and on the same plane. We achieve this through grinding with a belt or stone grinder or a combination of both.
A base high snowboard is unstable and difficult to control as the edges are not in contact with the snow when level.
An edge high snowboard is where the edges stand higher than the base has the opposite effect of a base high board. It is difficult to turn and feels like the board wants to track too much (i.e. stuck in grooves).
A base grind not only achieves a level base and edge configuration, but it also places a structure on the base. A structure on the base is essential to reduce drag and friction. Your board is basically riding on a thin film of water produced from friction between the board’s base and the snow. In wet snow we have too much water therefore we want a structure that will repel water and push it away from the base. We achieve this by having a deeper structure. Here the extra air sitting in the pockets of the structure force the water out and away reducing suction. In cold snow we have the opposite happening and as a result only need a fine structure.
