There are two separate factors in play: the size of the plane and the
cutting angle of the blade (and maybe the amount of blade support close
to the cutting edge).

A block plane (called because they were used to trim end grain on
butcher blocks) will have a bed angle of 12 degrees, but because the
blade is held bevel-up, you will need to add your bevel angle to get the
total cutting angle, close to 35-38 degrees. That angle is ideal for
slicing end grain.

When cutting face grain, you have a chance of tearout, and in general, a
higher cutting angle ( 45 degrees) reduces chances of tearout but
increases the difficulty of pushing the plane through your material.
See http://www.leevalley.com/shopping/In...asp?page=49520 for
some pictures of tearout. You could put a higher angle onto another
blade and use your block plane on face grain. (With traditional
bevel-down planes, your bed angle is your cutting angle unless you play
with back bevels on your blade...)

As for the size of the sole, it may affect your accuracy over large
surfaces but it is sure nicer to use a small plane where finer control
is desired.

- Daniel

Jacobe Hazzard wrote:
I've read that block planes, which are smaller and have a lower blade
angle than smoothing planes, are meant primarily for cutting end grain.

Is there any reason why a block plane with a 12 degree blade angle is
unsuitable for planing a face or edge? Is it simply a matter of taking
longer to remove the same material, or that the smaller sole is more
difficult to obtain square faces with? Is there another reason why a block
plane shouldn't be used to cut with the grain?

Thanks,
Adam