Update:10-14-2018: A fellow user has informed me that a design revision is required.
Consider this project a work in progress until further notice.
There are a variety of Kossel kits on the market that use 218mm effector arms and 240mm horizontal extrusions. Print area for these kits rarely exceeds 180mm, but the printers often have 200mm or larger build plates.
The purpose of this project was to increase the print circle to nearly 200mm. Theoretically, the print circle could be increased further, but my glass build surface is 200mm.
There are two versions; 16mm spacers increase horizontal extrusions to 274mm, and should result in a print circle of 197.3mm. 18mm spacers increase horizontals to 276mm, and should result in a print circle of 198.7mm.
The type of carriages you use can alter the result. My estimates are based on 12mm linear rail, but the modification is presently untested.
You'll need 18 spacers, and 18 M4x25 socket cap screws and nuts (washers optional)..
The parts seem to be more dimensionally accurate and rigid in PLA, but you know best.
These were a Tinkercad mashup for proof of concept purposes, so no source CAD.
If you are looking to build out to 220mm, then a remix to 32mm should get you to a print circle of 218.9mm. This is again untested, and the length of manipulator arms will need to increase as the print circle grows beyond a certain point, which then reduces vertical (Z) movement. With 218mm effector arms (center to center) your results should be within a couple mm, but no guarantee of exact build area is expressed or implied.
Whatever works for you. I'd suggest around 50%.
Tested with PLA resulting in a perfectly snug fit.
If using other plastics, consider rescaling to accommodate shrinkage.