starting from scratch- router 1st project

[idefix]

Hello, Jazz
Thank you for these valuable comments and suggestions. I have rebuilt the gantry with Hiwin style rails and blocs. size 15 for the Z axis and 20 for the Y axis and future X axis.
You are definitely right, the size 20 is almost same cost than size 15 for a much better strength...
I have tried my best to keep the Z moving plate as close as possible to the gantry beam (not so easy). Z axis travel is 170mm
Following your advice I have plugged the beams with covers (but do not decide yet where to place the plugs to fill/remove the dry sand)
To achieve correct geometry of the sitting planes for the rails, I can have access to a large milling machine at the company workshop (this will minimize the efforts of the alignment step)
The ballscrew type has been changed to 1610 for Y and Z axis and will be driven by timing belt ratio 1:1 (with space left to replace for 2:1 ratio whenever necessary)

Some pictures of the changes:




Again a few more questions :

Do you think it would be better to design a cover on the Z sides (to limit dust and debris penetration) ?
For lubrication, should I use grease (with the nipple) or should I already design oil pipes from now ?
For the Z axis stepper motor; should it be facing downward or facing upward ? (would depend mainly on the position of the ballscrew...)
Regarding the long X axis driven by two separate ballscrews and separate timing belts + motors, I plan to link the steppers on 2 different axis via mach3 sofware. Does its sound ok ?
Last question related to ballscrews: does the chinese ones so called "antibacklash" realy fit the requirements ? or should I go for the coupling of 2 separate nuts as exposed in Jonathan thread (a sufficiently strong machine) ?

Again thank you for your very valuable support.