[romihs]

Hello,

I have spent, what feels like ages, reading (and contributing a little to) the Epoxy-Granite Machine Bases thread, slowly putting ideas together of what I would like to build. Initially I wanted to build a mill, but have realized that a lathe is probably one of the first machines one needs, so I have decided to try build a CNC lathe with Epoxy-Granite (EQ).

My initial ideas were to use full length inserts for the linear bearing beds (and all other components that need to be bolted to the base) which could then be ground/machined true once the base/part was de-molded.
Looking at components manufactured by the pro's, I saw that they very rarely had large metal inserts. The reason for this could be any of the following:
- Differences in the linear coefficient of thermal expansion between different materials.
- Time saving.
- Cost saving.
- Something that I have not thought of yet...
Considering that I don't have access to any, well equipped, workshop, I decided not to use full sized inserts. Instead, I will spend more time building an accurate mold and use ground plates for the areas where the linear components and other hardware will be bolted to the base. All that will be cast into the base are steel treaded inserts.

Initially I planned to build a flat bed machine, but one thing kept bugging me; EQ is probably better at handling compressive forces than tensile forces, and the EQ will probably creep most when exposed to forces other than compressive (I do not have proof of this, it is only based on my understanding of the material and its composition). So I looked at the slant bed design and saw that this configuration would transmit most applied forces into the base, and not out of it (i.e. compressive).

Here is what I have come up with so far.


I decided to use a 60 degree angle.
The total length of the base will be about 1 meter.
The linear rails are 15mm wide, and I plan to order types with half-pitch bolt holes. I came across an SKF product range designed for use on these types of machine bases, who's mounting hole pitch is half that of the regular rails. The hole pitch will be 30mm, which will allow me to mount any standard 60mm pitch rails too.

The 'green' parts are EQ. As you can see I plan to use EQ for the cross slide base too.
I'm considering adding chopped fibers into the EQ mix for the cross slide base to increase its mechanical properties.

I won't be building much for a while yet as I do not have any suitable work space in which to do this, and a quick estimation puts the mass of this machine at about 500kg, so I need a pretty solid workshop in which to build this machine.
We are in the process of building a house, with a workshop in the basement.

I will keep updating this thread as I continue with the design.
Any suggestions and info would be appreciated.

Best regards

Sandi