There is a flat washer on the arbor or drive side and a cupped but flat faced washer on the nut side. Do not use 2 washers on the nut side. Starting at the arbor, you could turn one cupped facing out then the blade then the cupped facing in, then the nut but there should always be washers on both the drive side and the nut side.
Some times the arbor has a "built in" washer or flat face, then the inside or arbor washer is not required. The purpose is to hold the blade perpendicular to the shaft from both sides. With no washer or flat there is not enough surface area on the nut alone to provide substantial pressure to keep the blade perpendicular.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 08-16-2017 at 11:48 AM.