Facing tolerance for BB

CEarly said:

About how much could a 68mm bottom bracket shell be reduced in width by
facing operations before one might need to use a spacer to compensate for
the material removed? I've got a new frame whose shell was faced once and
is now 66.5 - 67mm wide.

Depends on the BB. But that sounds low.

Jasper

The consequence of having a BB shell slightly less than 68mm wide is usually
only that more thread sticks out of the frame on the non-drive side BB cup.
Unless the way that looks bothers you, there's probably no need to do
anything about it.

CEarly said:

About how much could a 68mm bottom bracket shell be reduced in width by
facing operations before one might need to use a spacer to compensate for
the material removed? I've got a new frame whose shell was faced once and
is now 66.5 - 67mm wide.

I suppose it depends upon how important a straight chainline is to you.
It would be more important on a fixed gear bike than on a geared bike.
If the shell was machined evenly on both sides, just split the
difference and get a spacer that matches. My '80's Schwinn Peloton's
shell was faced down to about 64.5mm. I am running a Shimano UN53
cartridge bottom bracket with a 2mm spacer on the drive side. This
works great, does not creak, and produces a straight chainline. (bike
is a fixed gear) I stuck an old Sugino lockring on the plastic nut on
the non-drive side to make it look presentable.