In article ,
"BigWallop" writes:

These are the best type I've used:

http://homepage.ntlworld.com/cooperhouse/fr_ha61.htm

I have one of these. It did about 30-35 boxes (counting twice
for double boxes) very well, but quite suddenly became ineffective
when it wore out (cutting edge became rounded). The square piece
in the kit was completely useless and would get stuck in the
hole -- squaring off the round hole was much more easily done
with a chisel attachment. So, the cost was something over £2
per box, or £5 for doubles, which looking back isn't cheap.

--
Andrew Gabriel