My goodness. Buy a good quality double bevelled hook knife. If you buy a cheap one you will get lousy results. Better yet, make one if your inclined.
A good double bevel is hollow ground on its back for an aggressive edge, is made with good steel and will hold an excellent edge.
The shape and size of the handle is very important on any knife.
We just made a set of 5 for a mask carver in Alaska. She has tiny hands. We made tiny handles.
Look at what aboriginal people and Seattle carvers carve from Alaska all the way down the coast to Mexico. Hundreds of professional carvers. They are not stupid. Double bevel hook knives are their main tools.
I would think if you're getting bad results...try again
Oh yeah, birch is very nice to carve.
Scott.
Double bevelled hook knives.