Bruce,

Another option you could look at with that build is two section of rectangular box section and bolt a backing plate or wings to them and bolt that to the gantry uprights as well as the box sections themselves. This will give a good bit more rigidity and either the wings or the backing plate could be indexed to help keep it all true and proper. Drop me a message and I can send you a few files in a format that you can use of ideas Jazz and I worked on that will work. Also take a look at my build log as there are some ideas in there you might be able to use. The following might help:

http://www.mycncuk.com/forums/showth...-machine/page6

If you scroll down you will see one model with sections lifted off to show an idea for the Y axis. That might be a good place to start from and change the solid rail to box or rectangular section extruded aluminium or steel and you would have something that would be a good bit more rigid then the channel. Just trying to help and hope not to offend.

Michael