[Dave Paine]

You have some nice pieces of curly maple. Most folks would love to have these pieces. Curly figure is normally a premium. You should be happy.

The "curl" is where the grain is coming out of the board. Hence mixed grain direction. Planing mixed grain can result in tearout, what you are referring to as "rough".

As stated earlier you can sand smooth. The alternate to sanding is using a card scraper. Inexpensive and very handy to have around.

http://www.woodcraft.com/Product/2020022/19046/Curved-Scraper-Set-of-4.aspx

 

[Dave Paine]

Thing is, seems to me, using a scraper on a board just seems impractical, not to mention a recipe for burnt thumbs.

What about a scraper plane? Could that possibly be a viable solution?

If you have not used a card scraper, you may not appreciate how easy they work when they have a decent burr.

A scraper plane will also work. Just a lot more expensive.

Most people using scrapers get fatigue in the wrist from holding. A scraper holder is less expensive than a scraper plane and will work almost as well.

http://www.leevalley.com/US/wood/page.aspx?cat=1,310&p=32669