On my little Cutty Shark router, I usually cut 3/16" lexan 1/16" deep and through cuts. I can cut straight cuts @ 150 IPM. Can set the rapids to 300, but set @ 200. I have to slow doen on tight curves to 80 IPM. 2 cuts gets me through the lexan using a PC 690 router, Thompson single nut ball screws, roller skate bearings on X and Y. Little THK RSR 12's on the Z. 425 oz 23's and 3 Gecko 203V's running on a 62 VDC 6 amp lab power supply and an IBM Thinkpad laptop.
I cut steel and aluminum on my mill. Steel sheet, I can run coated cheap EM's @ 6600 RPM feeding 25 IPM with .025 DOC. I use Koolmist 77 and a cheap HF solvent tank for the coolant system.
I can cut 6061 aluminum with a 3 flute coated EM @ 50 IPM. 1/4" mill drill for engraving, spotting and edging @ about 40 for edging and 150 IPM for engraving and spotting. Same speeds in steel for this.
The mill is using THK linear rails and preloaded ground ball screws. (Thanks EBAY)
The Z axis has a ready built IKO cast iron slide with the same NSK ground ball screws.
495 oz Keling motors withe 3 Gecko 203V's running off a Keling 72 VDC 12 amp PS.
It has an X2 R8 spindle running off a 2.5 HP treadmill motor.
I am very happy with both of these.
My little 7/12 conversion works well too, but not as strong as these two. Smaller motors, smaller PS and stock screws so far. I have another treadmill motor fotr it. Then I will be able to up the speeds. Right now I often stall the OEM motor. Undesireable anytime, but especially so for cnc.