There are a lot of choices out there these days. My advice is to do your homework, looking at it from a using aspect, and ASK a LOT of questions to those who sell, and those who own the machine(s) you're interested in.
You can go anywhere from "plug-n-play" to building your own..... only you can determine which direction is best for you.
Some basic criteria that must be present in any grinder, before I would personally consider purchasing it would be....
1. The grinder is made from heavy gauge STEEL. I know it's all the rage, and "cool" to have a light weight grinder, but light weight material/machines vibrate, chatter, and are overall less stable/less durable than solid/heavy weight ones made of steel. In addition, make sure the parts that make up the machine are SOLID steel, and NOT tubing. (In my opinion, if you look at a grinder made with steel or aluminum tubing...run the other way)
2. Steer clear of machine that have flutes or grooves in the drive, idler, or attachment wheels. Those who produce them will rave that the wheels are fluted/grooved to aid in keeping belts cool, but they are flat out dangerous. Sooner or later you're gona forget that those wheels are not contact wheels, and try to grind on them...... this same design (fluting/grooved wheels) was attempted back in the late 1980s.... and several people were injured, and a couple even lost eyes because the grooved wheels will shred a belt in a snap if you try to grind on them.
3. Steer clear of "non-standard" design elements...buy that I mean tooling arm size (the standard is 1 1/2" square). Nearly all the after market attachments for grinders are based on 1 1/2" tooling arm. If you choose a machine with another size tooling arm, you basically lock yourself into buying any future attachments from the source of the grinder. (most who use tooling arms other than 1 1/2" do it on purpose, in order to make things "proprietary") It also pays to ask questions about bearing sizes used in the machine(s). Sooner or later bearings will need replaced in the various "wheels" on a grinder...... if the machine uses "non-standard" bearing sizes, you can expect to pay 3-4 times as much for the maintenance parts versus "standard" size bearings, and in most cases you will have to go back to the grinder's producer to get them.
4. Some will certainly disagree with me on this one, but I am not a fan of aluminum tooling arms. Generally the producer of a grinder touts an aluminum tooling arm as a "feature" of their machines, but in reality is is something that leads to increased vibration/chatter, and gets "chewed up" over time where the "clamping" mechanism contacts the aluminum. Aluminum tooling arms are more expensive, lend themselves to vibration/chatter, and require replacement far more often then steel tooling arms.
Motor size is always a compromise between "what do I need", and "what can I afford". My input is that if you are going to spend the money on a "top end" grinder....... get the largest HP motor you think you'll ever need. I started my career with 1hp, then went to 2hp, and am currently on 3hp motors. Had I known then, what I know now, I would have ponied up the money for 3hp motors to begin with, and saved myself a lot of money in the process. My opinion is that you can always "grow into" a machine with higher HP...... but, if you have too little HP, you will grow out of it quickly, and the only option is to buy a larger HP motor/VFD.
Single speed or VFD? No question here..... VFD all the way. There is simply nothing else that will give a grinder more versatility.
Look at customer service....and I don't mean looking for it on the internet.... there are a lot of knuckleheads out there who have very little common sense, and want a grinder producer to "hold their hand" when they have no business with a grinder in the first place. If you can't grasp the concept of simple electrical wiring, or understand a 3 position start/stop switch, you might want to educate yourself a bit before jumping in. These are the people who make a grinder producer's life miserable, and then go on various forums and bad mouth the grinder producer for "not helping" when all that was needed was a bit of easy research and personal responsibility. Seek out and talk to people who own the machine(s) your interested in, and get as many opinions on customer service as you can. Most grinder producers are very good about service after the sale, but there are some, who simply would rather not ever have to deal with you once the sale is made.
And finally...... buying a grinder from an established source (if you're buying versus building) means that down the road, if you ever decide to sell the machine, you will either get your purchase price, or very near it, back out of the machine. Not many shop machines hold their value as well as a 2x72" grinder from an established source. Where as if you buy from one of the "Johnny come lately" sources, you have no idea on resale value.
In the end, it's up to each individual to do the research and acquire what they believe is best for them, what I've written here is just things that I have learned over 30+ years of buying/using grinders intended for Knifemakers. I share because I'd prefer to prevent others from making many of the mistakes I already have.
