My brother owns a Glowforge and there seems to be a common problem with one of the Gantry Wheels that keeps breaking. This is version 2 of a design that also seemed to shatter as well. Previous versions were printed 'horizontal' so that it seems that the Glowforce mechanism applies too much horizontal pressure and breaks the first versions. The design is vertical, which would put the layers at a 90deg to the force being applied to them by the Glowforge. Ideally, this would provide a stronger part.
It is suggested that you print at the highest resolution to provide more layers/strength.