We have found that large or hard pills are more difficult to get an initial crush. If you "nibble" at these pills, meaning that you crush a portion of the pill at a time, they break up much more easily under the crush block. The crushed pill is then ready to be pulverized by the roller.
While the crushing and rolling process is quicker than other methods, take sufficient time to crush and pulverize so that dissolving is quicker and more complete.
The finer pill material can be crushed, the less likely there will be clumps of medication that may clog feeding tubes.