I made these for an e-wheel project. They are made from 3" sintered metal casters that were purchased from Northern Tool for $5.00. They make excellent anvils. I'm not a big fan of "flat spotting" the radius because I believe a full radius provides better tracking and crown development (to each his own). A flat can certainly be machined very quickly --
There were made in an afternoon -- formed with a template and the final finishing was done with a file and emory cloth because the sintered metal flakes easily with a standard carbide cutter and low speed. My lathe doesn't have super high speed so i had to compromise.
The biggest factor in making these anvils is machining a sound mandrel on which to mount the casters for turning.
The first pic shows the machining process for the mandrel (just some scrap aluminum rod).
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image01.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image02.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image03.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image04.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image05.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image06.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image08.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/E-Wheel/Image20.jpg)