Originally Posted by
Doug Fattic
Tom it is much easier for an amateur builder to make a frame with horizontal long slot dropouts. This is because it is not necessary to nail exactly the chain stay length. You can get it approximately right by sliding the chain stays in and out of the BB shell’s sockets. With an eccentric shell it is necessary to get the miters and chain stay length just right. That is made much easier with machine mitering and an expensive fixture.
But why is it necessary to get the chain-stay length exactly right? Obviously if it's way off you will alter the whole geometry but a mm or so won't make any difference.