DIY mill...

[irving2008]

Some more calculations using the 'Framework' program.

Option 1 - 50mmx25mmx2mm aluminium rectangular tube for uprights 300mm high (50mm width in X plane), 1 length across the back at the top (50mm width in Z plane). 2 x 16mm horizontal precision rails centrally mounted at top on uprights vertically spaced 100mm (i.e one at 200mm above table and other 300mm above table).

Option 2 - 100mm x 19mm MDF for uprights, 1 length across back (100mm width in Z plane obviously). Rest as above.

in both cases the spindle mount is modelled by a 300mm long x 90mm x 10mm aluminium plate located centrally in Y plane, and at bottom of Z movement. There is 1.7kg dead load (spindle motor) and 20N force in both X and Y planes on the bottom of spindle mount.

The lattice and load diagrams are shown in the attached picture.

The interesting thing is that the X/Y displacement of the spindle tip under 20N load is, for the Aluminium version, 0.22mm/.003mm and for the MDF version is 0.43mm/.004mm which shows that an MDF version is definitely fine for PCB milling (where the load is much smaller) and can probably do lightweight aluminium work but the aluminium frame is prefered for anything more strenuous. These calculations assume all joints are perfect and non-moving. Another interesting thing is that the MDF version weighs 5.4Kg while the Aluminium one is 3.6kg (both including the 2 x 16mm rails and the 'spindle mount'). Aluminium is definitely the way to go, its considerably lighter and more rigid (but not significantly so - doubling the force doubles the offset but thats mainly in the distortion of the spindle mount and rails rather than the frame).