There are a bunch of really too notch machines out there for knife makers.
In my opinion there are really two that rise above the rest. The TW-90 (
https://traviswuertz.com/?product=tw-90-knife-grinder) and the Northridge tool grinder (
http://www.northridgetool.com/).
I don't own either, I just can't justify the expense for a hobby. I have a Reeder (
https://reederproducts.com/) which I think is an awesome grinder! There are lots of options out there for grinders. Just remember to buy the one that has ALL the features that you want/need (you want and need variable speed). Buy once, cry once, as they say!!