What is the best way to make a rhubarb plant multiply so you can get about a 2 foot area of rhubarb?
Grind isn't the word I would use. More like split.
What you want to do is dig up the plant. You dig 6-8 inches deep all the way around, then pry the plant up out of the ground. If the plant is relatively old, this may be difficult as the roots can get very tough and wooden.
Once you have the plant uprooted, you split the root mass. You want to have one to three buds per section and at least a fist-sized clump of roots. Plant the sections with the top-most portion of the roots 2 inches deep and you're good to go.
You should not grind it. It is not like horseradish which you probably could grind up to multiply.
Rhubarb you need to let it multiply naturally and divide it after its growing multiple crowns. It's a slow process, but it's the only way to go. You could always buy more crowns.