shaft support bearing placement

Hi everyone,

I'm designing a machine with a rotating shaft and I'm not sure if the support I've choosen for the shaft is good enough. Here's how the whole thing looks like:

http://farm3.static.flickr.com/2631/...3265ec4b_o.jpg

Legend:
Blue - those elements will be connected by a toothed belt and rotate
Green - shaft, rotates as well
Red - bearings (you can actually only see one of them on the drawing, but they are places in the top two support plates)

The shaft lenght will be around 120-150mm, but probably not more. At the end of the shaft there's a burr which is part of grinding burr set. I can't really place a support bearing at the end of the shaft where the burr is as I need the bottom to be clear of any obstacles. The upper support plates are 20mm apart.

So the question is, do you think that with a shaft diameter of 20mm the two top bearings will guarantee sufficient support? Perhaps I should use roller bearings instead of ball bearings to get more stiffness?

Regards,
Tom