thx for the link very interesting
I have changed the design of the machine a bit
Everything will be made out of 80x80x4 mm thick steel
My gantry way's about 50 KG of steel.
I think the supported rails way about 6.6kg and the Z AX about 10 kg .
So in total ist about 66.6 kg but maybe take 80 kg just to be sure.

can i use these motors with a r&p system?
i was thinking going the mechmate way : they hold the pinion against the rail with a spring.

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the machine is still in design fase so i can change a lot so if u guy's have more advice let me know

thx