blue_can,
Three other popular designs are the Rockcliff, JGRO, and Joes CNC Model 2006 and you will find the info for them on CNCzone. There are others out on the internet.
Solsylva plans are intended for first time builders who don't have a lot of tools and the cost is kept low by using locally available parts as much as possible. The general machine designs are good, but the hardware can be improved on.
There are a lot of people who built machines from the Solsylva plans and made changes to the dimensions to allow use of larger and better leadscrews, anti-backlash nuts, larger bearings, and made the machine larger for their needs. The plans are very detailed. If you are going to deviate from the plans you will have to understand how the hole locations will need to be enlarged or moved in order to accomodate the larger or differently shaped parts. The 25x37 and the larger belt drive machine plans are very open to design improvements to make them much better than if built strictly by the plans. People are successfully using the 25x37 to make guitar bodies, R/C model kit parts, and 3D craft objects.
The first thing to change is the use of pine lumber. Use something more stable and harder. The second thing is don't use all-thread rods. They will work, but few people have been happy with them long term. All-thread rod is rough, inaccurate, generally not straight, and very slow when it does work without binding.
CarveOne
CarveOne
http://www.carveonecncwoodcraft.com