As my first venture into 3D machines still works well after 1,5 years running. Now I have changed a little of the delta design, making it more and more precise, adjusting a couple of thing here and there and ran into the discussion with a friend of mine concerning the precision of the stepper motors I currently use. They are of the very cheap chinese (robotdigg, 6,5€) sort.
Of course I do beleave, that with more and higher quality components it will run even more precise, but I would like to hear from you what Brand of stepper motors are reasonable in terms of price and precision. I have been happy with the cheap chinese NEMA 17s, in combination with the RAMPS, but have now changed to a RADDS and would be interested in what you think would be appropriate.

Stay with the chinese ones?

Have one from brand XY?

... looking foreward to your comments!

On a delta I think it is worth using 0.9deg/step motors instead of 1.8deg/step. They don't cost much more, but they improve the positioning accuracy, in particular along the Z axis. I recently received my 0.9deg/step motors and will soon be upgrading my Kossel with them. I can't advise you on brands, I have only used Chinese ones.

If you are into upgrades, I recommend Duet electronics. You get a great web interface, digital control of motor currents, and 30-second delta auto-calibration. If you don't already have FSRs or another good Z probe solution, you may also be interested in my differential IR height sensor. See [miscsolutions.wordpress.com] for details of my build.

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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].