calibration & DELTA_PRINTABLE_RADIUS

Hi,
My setup: Kossel mini, Arduino mega 2560, Ramps 1.4, bed 170 [mm].
Using latest firmware (latest to last week )
Still doing calibration.. all seems to be OK.
1. I arrive to "Set and test Z-probe retract position" as explained in here, I think I miss something.
My bed is 170 [mm] since DELTA_PRINTABLE_RADIUS = 70.0
my minimum Xmin= -70[mm], Xmax = 70[mm] same in Ymin=-70[mm], Ymax=70[mm].
In order to arrive to the Z-probe retract position the hot-end need to be outside the bed but I can't arrive to that location.
As far as I've understood that (shortening the printable radius) is done in order to correct the concave/convex at the end of the bed.. [so I'm not sure I should increase DELTA_PRINTABLE_RADIUS to 90.0 ]
What should I do?

2. What will be considered good calibration? (regarding concave/convex values at center V.S outer locations) is 5 mm is allot? is 1 mm is very good?
Best regards.

Printable radius only effects the area of the bed that the printer can effectively print in. The numbers that you stated above are incorrect because if you have a 170mm diameter bed, the your printable radius will be +/-85mm, not 70. If 70 is correct then change your delta diameter to 140mm.

Getting rid of the concave or convex shape in the printer is done by either changing the "delta smooth rod offset" or changing the delta radius in the host firmware like M666 R(number)... Like M666 R120.

Good calibration would be a difference of +/- .03mm. You should follow the paper test in calibrating the towers: [minow.blogspot.com] or [reprapandme.blogspot.com].

You can check your current settings by entering M666L, and save any settings that you entered by punching in M500.

Start with the towers: Y, X, Z. Then center. If the center is off, I find it better to just change the delta radius in the host via the M666 R code, rather than changing the smooth rod offset.

You will also need to adjust the enstop heights to account for any issues if let say X and Y are at z0, but Z tower is at +/- 2. You can change the z tower enstop offset by entering M666 Z-2, and test is that makes the nozzle move to the bed at z0 when then Z tower corridinate (G1 X0 Y90 Z0 F8000) is entered.

Edited 4 time(s). Last edit at 08/18/2014 10:43AM by Wildcard.

Wow! thank you for the detailed answer

Edited 1 time(s). Last edit at 08/18/2014 02:45AM by polkary.