A knife holder assembly for a rotary cutting machine includes a holder with a top portion and side portion each including an opening, and an adjusting member with a top portion and side portion each including an opening. The inner side portion of the holder is tapered at an angle substantially the same as the side portion of the adjusting member. A fastener can be inserted through the top portion opening of the holder and the top portion opening of the adjusting member thereby moving the adjusting member in a direction away from the outer side portion of the holder to clamp an inserted knife between the backing portion and the outer side portion of the holder.