Just a thought, but has anyone been to the beach recently, there are plenty of shells (like limpett) which are quite hard and very smooth internally, in theory you could epoxy (or use a natural glue) one of these into your bearing block.
Because it is smooth it reduces the friction on the drill and anything that you wish to use (an oily leaf like holly) can be used as a lubricant. There is the bonus that it is not as heavy as carrying a pebble in your kit. :-D
Because it is smooth it reduces the friction on the drill and anything that you wish to use (an oily leaf like holly) can be used as a lubricant. There is the bonus that it is not as heavy as carrying a pebble in your kit. :-D