Summary

Replace the stock bed bearing support plywood with self-printed parts that allow you to print edge-to-edge on the existing bed with only $25 in additional parts. This will increase print width from 100mm to 185mm (as shown by blue tape in photo)

Optionally use with the Printrbot Simple Metal Print Bed For Build Volume Upgrade to increase print width to 275mm.

Instructions

VITAMINS:

1 36" 8mm polished rod (McMaster 88625K67) - buy extras for other projects ;)
4 3mm x 12mm flat head screws (McMaster 91294A132)
1 PrintrBot GT2 Kit (belt and 2 pulleys - $20)
2 608 (skate board) bearings (McMaster 5972K222)

Option 1 - increase to 275mm print width
4a. 1 Printrbot Simple Metal Print Bed For Build Volume Upgrade ($30)

Option 2 - increase to 400mm print width
4b. 1 "Build your own bed"

TOOLS

Working CALIBRATED printer with at least 100x100 mm build volume
Calipers (i use cheapo "Neiko 01407A" from amazon)
8.0mm and 2.5mm drill
Allen wrenches for 3mm socket, 3mm flat head and really small for GT2 pulley set screws
Heat gun or hair dryer
Hacksaw or 3.5" die-grinder with cutting wheel

PRELIMINARY (but not short) INSTRUCTIONS

NOTE - all prints were done by author using KISSlicer.

If you are printing on a stock simple print these parts WITHOUT SKIRT:
1 simpleLeftEnd.stl
1 simpleRightEnd.stl
1 simpleRightBed.stl
If you are printing with a 150mm x 100mm build area print (skirt ok):
1 leftEnd.stl
1 rightEnd.stl
1 rightBed.stl
For all printers print (skirt ok):
1 MotorMountXGT2.stl (same as in thing 194686)
2 BearingCap608.stl (same as in thing 194686)
1 washers.stl
1 rightSupport.stl
1 leftSupport.stl
Clean plastic rod parts (leftEnd,RightEnd,RightBed) by running an 8mm drill into rod holes and a 2.5mm drill into all the tap holes. A small amount of material should come out but if you get a lot calibration or slicer setting aren't right
Take your new rod and cut in half to 2 18" pieces. I used a 3.5" die grinder with a cutting wheel, hack saw should work. After cutting sand the ends to remove any burrs. Note using 18" rods allows you to upgrade bed without making new rods. You can make rods shorter once you decide what you want
Test fit and adjust rod parts (leftEnd,RightEnd,RightBed) to the rods. In my case the rods didn't quite fit. So I used a heat gun to LIGHTLY warm the thin areas of the part until the rod fit - about 5 seconds on low. DO NOT heat so much that the part gets floppy. Assembles as follows: put leftEnd on the left end, slide rightBed onto the right end and slide down some then put rightEnd on right end. Once assembled remove the leftEnd while leaving other parts on the rods
Install both 608 bearings onto the MotorMountXGT2 using the BearingCap608 cap and a 12mm (?) cap screws.
Use the caliper to measure the distance between the top of the bed and the bottom of the bed bearing carrier in all four corners. Pick the shortest value then the subtract that number form the other three. The corner with the shortest value will be mounted with no washer and the value calculated above will determine the washers to use in the other corners. In my case the left and right sides were the same...
remove the bed, string and bed carrier and rods leaving the bearings attached to the bottom
remove the all right side screws, all bottom screws and screws into x motor plate on the left and top side. Remove motor screws
remove right side, bottom and x motor plate
test fit MotorMountXGT2, file/adjust as needed
position GT2 gear between 608 bearings then slide motor through MotorMountXGT2 into GT2. Screw motor to plate, tighten GT2 gear to shaft
put MotorMountXGT2 into position, reattach bottom and right side. screw everything together.
Cut GT2 belt in half. Feed between gear and bearing, around gear, then between other gear and bearing. Pull one end and slide into an end grabber.
Slide belt into other grabber as tight as possible. Thread 3mm cap screw into tap hole at end of the back rod on either left or right side. Tighten screw to add tension to belt - make sure to slide from part to stay square.
Position bed with wider screw/edge gap towards the back put a screw through the corner with no spacer (measured above) and screw in 1/4 of the way
put the other screw on the same side using the washer with the thicknes calculated for that location between the arm and the bed and screw in 1/4 of the way. Repeat for other 2 bed screws.
tighten all bed screws
Install the rightSupport and leftSupport using the screws holding the back support plate. The legs should angle forward. Note - lay the printer on the side so that the nuts don't drop out when you remove the screws.
In Repetitier edit printer settings -> printer shape and change X Max to 190 and Print Area Width to 190
In KissSlicer edit printer -> hardware and set bed size X to 185 and bed center to 95 (home position is approx 2.5mm off left edge of bed)
if you find that the printer stops at 100mm you will need to inform the FIRMWARE about the new limits. In the manual control tab of Repetier run "M208 x190" to increase the firmware limit. If it works run "M500" to save your new limits. You can also use Config->Firmware EEProm Configuration command to do the same thing

Try printing bigBox.stl to test the limits of your new bed using the VASE setting WITHOUT a skirt. Note - big box current goes around the back bed screws as I haven't got the flat head screws yet and I'm using cap screw which would hit the hot end

That's all...

PrintrBot Simple X-axis GT2 Belt & Extension