I have found a faster method of cutting soft metals like aluminium by hand. Looking on ebay at the great variety of hacksaw blades on offer, I found some double sided ones with 24tpi one side and 8tpi on the other. They were cheap, so I bought some and tried the 8tpi on a bit of aluminium about 32 x 25mm and with AC90 lubricant,it took 1/3 of the time that an 18tpi would take. Probably not up to cutting steel, though.