Re: [CAD_CAM_EDM_DRO] selecting linear rails ?

excellent mail and question !
lets hope someone has an answer ..

btw- for part of the answer ...

it depends on
1.the size of your cutter (radius),
2.material being cut (stainless 316 or titanium vs wood),
3.the speed you are cutting at (1 ipm or 50 ipm[wood router vs. milling
hard material like inconel]),
4. and whether you assume you have no other force components (flexing,
bending) in your fixtures, workpiece or cutters.

my rule-of-thumb (feeling, i may be mistaken here), is about,
20-50 kg force for 1-2 hp milling with MT2, R8, (baby bridgeport, M2,
small mills), mild steel, about 8 mm end mill (1/3")
100 kg for a VMC, over 10hp head, ISO NMTB40/NMTB50 taper or similar
5-10 kg for a high-sped spingle (10.000 rpm), 2-4 mm end mill

FWIW:
In my mill I am building I assume 50kg load, and stiffness must be less
than 0.01 mm of flexing of structure
(the milling head cutter will flex appreciably more).

(My mill will be 1400 x 2800 x 200 mm work area, with BP M2 head as spindle)

Your needed stiffness is a function of the load you want, i.e. how hard
do you want to drive it,
which is a function of how much horsepower you have at the cutter to
remove material,
as long as the cutter does not bend and neither does your structure.

How much HP do you have or want ?
How fast do you want to mill ? (wood at 100 ipm or engrave at 2 ipm)
What material ? (balsa vs stainless 316L)
How accurately ? (0.3 mm or 0.006 mm)
Whats your envelope (this translates to your moment, or bending arm) ?
(6"x6" or 3'x8')

This gives you needed weight, stiffness, structural material.

Best, h.