We identified three overarching milling machine configurations: horizontal, vertical, and gantry-based. Here, we analyze two possible configurations we can replicate for our final project!
For the second post, describe two milling machine configurations. Discuss the manufacturability, adjustability, and potential challenges of building a machine in those configurations.
Gantry
A gantry-based mill would be lighter and would take up less area on a workbench, which would be attractive for our new, home-quarantine lives. It also has the potential for machining a surface with multiple tools, but this may be a stretch to complete in a semester. The gantry milling machine would be time-efficient and quite rigid, which could also be beneficial when applied to a tabletop system.
However, a large drawback is the restrictiveness of the machining space, as we are restricted to only working on material that fits between columns of the gantry.
Manufacturing may prove difficult, as there are many parts to machine, and it would add
complexity that the vertical or horizontal system may not incite. For instance, the gantry itself would have to be modelled and manufactured, along with a door frame and the horizontal bed. It may be most effective to build a bridge design with a nonmoving gantry to allow the Y and Z axes beams to not have to travel along the X axis. We also thus need to decide on the moving X axis (gantry or bed), and construct the rails for that motion as well.
Although this machine seems to be highly coveted in industry for efficiency and rigidity, it seems overly complex for our final project.
Vertical Mill Configuration
Like a drill press, vertical milling operations have the tooling rotation running vertically (in the direction of the gravity). A simple vertical CNC mill will have three axes where the tooling moves vertically; the table moves from front to back of the machine, as well as from side to side. These machines are common in many machine shops because they are cost-effective, simple to program, but still offer diverse capabilities.
There are two types of vertical mills -- turret machines and bed machines. The table on a turret milling machine can move both left and right and up and down, while the spindle remains stationary. The table on a bed milling machine only moves horizontally, perpendicular to the axis, while the spindle runs parallel to the axis.
A major disadvantage of vertical mills is that they often have lower-horsepower motors than horizontal milling machines. Compared to horizontal mill machines, they do not offer as fast of an output rate.
For our purposes, a major point to note while designing a desktop vertical milling machine like the one shown to the right is compliance in the linear rails due to the spindle action. A t-rail with a higher moment of inertia might be better that the circular rails used in this mill. If the spindle is causing the rails to bend then the precision of the machine will be very low. Another thing to keep in mind is the vibrational errors due to the spindle action. This can be reduced by attaching the mill to a large casted body to absorb most of the vibration.