Fodder,
1/ The flange on a bearing outer race is to locate the bearing and in regular groove or deep grove beaings don't provide any increased capacity to carry thrust loads. A flange on these type of bearings is usually just another option, like, shielded, sealed etc and doen't change the load ratings.
2/ The bearing can take a small side load, even though that's not the intended use for them. For home / hobby cnc, skate bearings which are not thrust or angular alignment types can carry enough thrust loads to do what a mdf router needs. Locate the screw, put it under a bit of tension and carry the loads of the gantry and cutting heads motion. Sure they're not angular contact types but a deep groove skate bearing's thrust rating is probably more than many mdf router gantrys can stand and cheap enough you can quickly and easily replace them if need be. EDIT: just looked them up and a typical skate bearings static load ratings start around 1kN or very roughly 100kilos or 220lbs.
For the 'backing plate' just drill the hole large enough so it clears the screw AND inner race but traps the outer race only. It's the outer that needs locating and you can use the nut against the inner race on the scew to put the screw under tension.  |