So finally got time to finish quite some modifications I had in mind for the annoying 'features' on my FT5.
1 - Pulleys and their bearings
I didn't like them and replaced them a couple of times in the last weeks.
I designed some new parts for the pulleys : for both Y-belt drives and for the X-drive.
The bearings used are F625ZZ type (16mm x 5mm with flanges). They are both mounted with the flanges to the outside to form one pulley. I used a 25mm long 5mm bolt for mounting them. See pictures and designs on http://www.thingiverse.com/thing:1958418 I splitted the left X-support to make it easier to print without support. The support part for the pulley is now a separate item.
2 - I didn't like the melamine parts
I replaced all corner brackets with aluminium ones already.
The support for the bed isn't my favorite and I made an aluminium replacement from 2mm thick profiles that is much more rigid in all directions. And now it is mounted, there is a clear difference. It doesn't move in X or Y direction. Partially also because the connection between the support and the bearings is very solid. This was not the case with the melamine and can be seen when dismounting.
3 - close the printer for printing at higher temperatures (ABS-HIPS-Nylon)
I used standard prolycarbonate plates (3mm thick) fixed with magnets to the frame for easy removal.
Next : replacing the heated bed with a Keenovo 230V 750W heater.