I have been thinking about different materials for the base board. Aluminum is definitely an options. But after some consideration, I decided to use wood. It is very easy to cut and shape, and has great strength weight ratio. It is cheap and easy to acquire too. The only downside of it is that the bulk of the size needed to reach the strength needed. But that is an acceptable trade-off for this build, as I can always replace them later. So here is the top plate of my Z head, with holes drilled for mounting.
These are assembled together as below, with a 300W spindle (which I also got from Ebay) mounted on the tool holder.
Next, we need put together the linear drive. For the Z-axis, I used a simple threaded rod going through a HWPE block. The HWPE block is a low friction plastic and is used here to achieve low backlash linear drive. It is a very simple setup. The threaded rod is hold with flanged bushing that fits into the wood blocks. The bushing is made of bronze with built-in lubrication. Two nylon insert lock nuts are used on each end as the holding points (which rides on the flange of the bushing). The stepper motor mount is made with an angle aluminum with a few drilled holes. Again, the coupler is purchased from Ebay.
Here is how everything are put together. A few more nuts are added for mounting the Z-Head plate to the Z post.