Z-Axis design and advice

[JAZZCNC]

If you have to use the unsupported rail then yes it's ok and just about the only way you can do it.!! . . . BUT it will struggle with Ali.!

If you can use supported rail then you would be best advised to change things around.! Put the rails on the front plate and the bearings on the rear plate.

This will give you maximum strength because the rail supports the front plate but more so because the distance from cutter to bearings is proportional to the Z axis extension. Less extension more support.
The way you have it now the distance from the bearings to the cutter tip is always the same no matter the Z axis extension and therefore the amount the front plate can or will flex is always the same.
When cutting hard materials like Ali this extension is very impotant to finish quality.!

Edit: On reflection if you have to use the unsupported you could still swap the rails/bearings and gain by reducing the extension. There will be slight strength gain to the front plate because you'd have to put braces top and bottom to clamp the round rails which will help slightly but you will always have the negative of unsupported rails potential to bend and flex.!! . . . . Hence why supported is better.!