I would use a router "hand held" with an edge guide and a 45 deg chamfering bit. A clamped on piece of wood could be used as a stop to limit the router travel. The chamfering bit likely will have a guide bearing on it, and this will be great for the final pass, but use the edge guide and not the bearing to make at least one light pass at each cut to prevent chip out. Then remove the edge guide and use the bearing to guide the router for the final pass.
If you have cut the wood from the trees yourself, have you dried the wood properly? Wood with more than about 8% moisture content will not remain straight and you will be wasting your time trying to use it until it is dry as it will warp and twist significantly while drying. Make sure it is dry before you try to make anything from it.
I've spent some time in your country, mostly in the Blansco, Adamov, and the Moravian forest areas. It is a beautiful place, and I would love to go back.