Theoretical / Ideal Maximum Bed Radius

I was wondering if there was any information on the theoretical or ideal maximum bed radius for a delta printer.

My Rostock Mini Pro came with a 160mm (?) acrylic plate that I replaced with a 9in (?) glass bed from a silicone cheesecake pan. But setting a radius of 85mm in my Slic3r settings has the arms nearly vertical at times and occasionally appear to be past the 90 degree mark for some moves. Just wondering if I am setting the build area to big, especially when using RepRapFirmware's autocalibration routine.

My diagonal rod length is 184mm with an approximate delta radius of 84.3mm if that matters.

The golden rule is the arms should be at 60 degrees when the effector is centered and at 20 degrees when it is furthest from the center. Feel free to break the rule

Thanks, I will check that out.

RRF should be OK with the arms going past the vertical, but if they go much below 20 degrees to the horizontal then you may need to restrict the travel speed to avoid the step rate going too high.

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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].

You may have a look here :
[reprap.org]

For the record, the rostock max from seemeeCNC do have arms which goes past 90°. This is possible because the belts are buried in columns
They recently increased the arm length to something more in line with the annonced usable diameter.

Haven't measured it yet, I don't have a compass currently (or is it a protractor?), but watching the rods move during an auto-calibration it looks like I am right at 20 degrees when probing opposite the towers. I rarely try to print anything that large, so I might shorten the probing points somewhat. The wizard on the Escher3D website is great for that.

Otherwise, between my recently upgraded Duet board, a new roll of ESUN Silver PLA, and directly using Slic3r 1.2.9, my printer has been working really great the past few weeks.

Thanks for the input everyone and the link PRZ.