Now I have the feeling you both are gently steering me away, back to extruded aluminum rail style, which is not a bad thing because I'm very opened to suggestions.
The design changed so many times, I'm used to it already.

The rigidity of the frame and the printing itself comes first, than the difficulty in mechanical tuning and maintaining the printer in time. The cost is the least important for me, but I will try to find the best deals for the same quality parts.
That's what steered me away from Robotdigg in the first place. I thought I'll redesign around smooth rods for the same rigidity, less hassle with China shipping and language barrier.

In the mean time I found extruder linear rails with bearings, 100Km from me . I can even pick them up if I want to, to ensure quality. It's the same company that sells the smooth rods
So please be blunt, will smooth rods give me a headache? I want a minimum 400mm XY and 400mm Z print space.
I was wondering why the Fisher company gave up on the design, and the smooth rods are not very popular with delta style.

Edited 2 time(s). Last edit at 04/30/2018 06:32AM by Gheorghe.

It's not only the smooth rods, but perhaps crappy chinese linear ball bearings, which spoiled the game for Rostock Deltas in the past.
We have now much better linear sliders from IGUS and some people even build their linear motion systems with PTFE tube. Maybe it's the right time for a Rostock resurrection?

The Fisher design wasn't given up on, you can buy the kit here [reprapltd.com].

If you are considering using linear rails, take a look at my Kossel variant here [miscsolutions.wordpress.com].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm interested in this as well, I really like the look of the linear rails, 3KU v2017 has an IMO really pretty take on how to stiffen up a printer using linear rails for it's support.