Werehatrack wrote in message . ..

(obviously) has a Presta valve hole. This is a pretty narrow rim,
skinnier than any of the otehr mtb rims I have, and double-walled.
Since it's terra somewhat incognito, I'm a little dubious about
reaming that hole out to take a Schrader valve's stem. On the other
hand, I'd prefer to have just one kind of tube in the stable if
possible, but it's not critically essential. Can anyone vouch for
having done this wthout trouble? Or should I just get the tube that
fits (and a spare) and be done with it?

A search for rim + drill + presta + "jobst brandt" will find
this comment, which suggests that a bigger hole in a narrow rim
is a bad idea--the narrowness of the presta valve was one reason
for its use in bicycle rims. Further searching along the same
lines will produce more extended comments.

from a posting by Jobst Brandt:

I hope you realize that the hole for a Schrader valve is larger than
one for a Presta valve stem and that the rim is a compression
structure. As the hole you drill in the rim gets larger there is less
cross section to support the spoke tension that puts the rim under
about 1000 lbs compression. Spoke holes are large on the bed of the
rim and small at the back side. The Schrader hole, on the average
removes as much wall from the rim as a spoke hole, the Presta does
not. The larger hole in the back side of the rim weakens it locally.