Been talking about a 5 axis CNC machine for quite some time now. Since no one is going to be donating one anytime soon… we are going to build one.
We were considering using iron castings. But really don't want to wait the 4 to 6 months for the casting to be stress relieved. So we are mostly going to base it on H beams (roughly 9in tall by 10 inchs wide). http://www.lbfoster-pilingproducts.com/pdf/HBeamTechnicalData.pdf
Once surface ground they will have a nice locations for linear rails as the flanges are just over an inch thick.
Unfortunately the H beams alone won't dampen the vibrations of the machine enough. So we will fill the H beams with epoxy granite, a blend of epoxy, sand, filler and other aggregate. http://en.wikipedia.org/wiki/Epoxy_granite E/G has about 10 times the damping of cast iron and is widely used in making precision machine bases.
For the A and B axis, we will probably use something like: http://www.sherline.com/8700inst.htm For the price its very accurate. Maybe some day we can upgrade to something like this: http://www.motionindexdrives.com/rotary-turntable.php At roughly 4k a pop. Motor for rotary: PK569PMA-R28
So with all that attached to the head and the spindle we will need some way to counterbalance the weight. So we will use something like: http://www.indgassprings.com/pages/prod_tension.html
Pneumatic tension springs.
We still need to pick a spindle, one with auto tool change ability. And all sorts of other little bits…. should be fun.