As most of you probably know, I tend to use a belt grinder for most of my rough shaping and bulk material removal. It's fast, easy, and once you get used to it you can do all kinds of shapes. However it has limitations: tight corners are almost impossible to get into, convex curves can be difficult unless you use a contact wheel instead of a platen, material sometimes comes off too fast, etc. For a lot of pipe shapes, a disc is simply better since it allows you get into areas that a belt sander can't get to - even with a small contact wheel.
For a while now I've been tinkering with making an attachment to the arbor I sell, but I've completely abandoned that. The reason is that there's a resin-bond disc that I've recently discovered that pretty makes what I was working on useless. And, frankly, I'm not the least bit upset about this at all - since it makes my life sooo much easier.
The manufacturer is Ali Industries, and the brand is Gator. The product is GatorGrit 50-Grit 5" x 5" Zirconium Oxide Sanding Disc and they can be found at Lowes (#250978), Ace Hardware (#2102994), True Value, and any number of places online (though, oddly, not McMaster-Carr). It's got an "ultra-power" or "power-plus" trademark on the package somewhere. It's a hook and loop disk, so it will slap right on the standard 5" backup pads. One disc will last through several pipes, and they're very inexpensive. I actually use a thin interface pad to soften the disc slightly and create some flex in the edge so that it rolls over slightly - this is the Abranet Interface pad available at Woodcraft and other places.
The abrasive they use is harder than aluminum oxide, and longer lasting than silicon carbide. They call it zirconuim oxide. Near as I can figure, it's a marketing term for zirconia alumina. Either way, it's good stuff.
So, if you've got my arbor and backup pad setup, run (don't walk!) to your closest Ace, Lowes, True Value, or online retailer and pick up a 4-pack. You might like what you get!
If there is sufficient demand, I can offer these on my site as well. Please post questions if you've got them.