EDITED: some of the holes were off a little. and the screw holes are really tight as well.
This is going to be how the axis on the BotBQ will be working. The rails are from Propsfactory on Thingiverse, but had to be modified to 15mm size for Openbeam, but the vwheels are the same size. I created the mounting plate in TinkerCAD and have published it to Thingiverse as well (links below). The bearings are 624zz size and I use two of them on the bracket. The mounting plate still needs some work, but I will update it on thingiverse as improvements are made. Its best to get the bearings in the vwheels as soon as they are done printing as it is easier to put them in there when they are still a little warm.
Openrail and V-Wheel from PropsFactory: http://www.thingiverse.com/thing:25081
My modified version for 15mm openbeam: http://www.thingiverse.com/thing:105833
This thing was made with Tinkercad. Edit it online https://tinkercad.com/things/fsuo7bBetdQ
M3x6 - 2
M3x8 - 4
M4x16(or 20) - 4
M3 - 12
M4 - 32
M3 - 6
M4 lock-nut - 4
624zz - 4
Printed V-Wheel from Propsfactory:
Printed OpenRail for 15mm Openbeam:
I suggest having already printed the V-Wheel from Propsfactory and inserted the bearings into them. If you are going to use this rail system, printed and attached the 15mm Openrail for Openbeam from the links above to your openbeam sections... and of course print this mounting plate as well.
Also, once you have the plate printed it is advised to lighty go through with 3mm drill bit through the M3 holes and 4mm drill bit through the M4 holes.. just in case they are a little tight.
The two M3x6 go through the bottom of the plate, make sure to add a washer on each side of the plastic, then lightly attach a M3 nut
The 4 M3x8 go through each of the upright holes, make sure to add a washer on each side of the plastic, then lightly attach a M3 nut.
The 4 M4 screws go through the four outer holes, add one washer before inserting, and 6 washers after, slide the v-wheel/bearing on and add another washer before finally screwing the M4 lock-nut and securing it tightly.
Slide your openbeam lengths gently parallel to the plate while fidgeting with the M3 nuts to make sure they align correctly, tighten all M3 cylinder screws to 'just enough' ;-) and BAM you got it.
Now slide it onto your printed openrail and your ready to go!