In either case however sanders are generally more precise and gentle tools than grinders. Orbital sander which should you get.
Belt Grinders
Belt grinder vs belt sander. Belt sander has a rotating sander belt that is made up of sandpaper. A belt sander is used for sanding mostly wooden material. For example while a belt sander is designed for rougher work palm sanders are designed for more precise finishing work. Truth be told most sanding projects cannot be completed with only one of these tools. The belt grinder belt speed typically runs double from what the belt speed of the belt of a belt sander is running at. The belt sander can be utilized as a lightweight belt grinder by buying belts that are meant to be used on metal.
One main reason is that the bench grinder is specifically made to sharpen tools and other dull implements. This equipment has a belt of abrasive metal that helps in grinding the metal. Bench grinder vs belt sander for sharpening it is hands down that you would choose to use a bench grinder over a belt sander when you need to sharpen tools etc. Belts grinders you generally have multiple grinding points such as the platen and the second grinding point is the contact wheel. And although an orbital sanders leave considerably fewer scratch marks than belt sanders these marks are still noticeable. Belt grinder is used for grinding the metals for industrial purposes.
One example of that would be when trying to remove old paint from a metal surface. However belt sanders are limited when it comes to sharpening efficiency on steel materials and can lead to heat buildup faster due to the sanders higher speeds. You will need a belt sander for aggressive and heavy duty sanding and shaping.