Cricket Bats are made from Willow. English willow is by nature a soft fibrous reed, its performance and durability are enhanced by drying and pressing.
The knocking in process
At the stage when the bat is purchased there are different ways of preparing your bat for the knocking in process.
Raw linseed oil should be used to moisten the surface of the bat and enable the fibres to become supple and knit together, forming an elastic surface. This is more likely to stretch on impact, rather than crack. Raw linseed is used, as it stays moist for longer than boiled linseed. About a teaspoonful should be applied to the surface of the bat.
Oil should be applied twice before the process of compressing the face begins. Each coat of oil should be about one teaspoon full. Spread the oil over the face of the bat using your fingers. Spread leftover linseed oil over the edges and toe of the bat. Let each coat of oil soak in overnight and repeat the process before starting the knocking in with the mallet. ( Always rest the bat flat when drying)
When the oil has been applied the knocking in process can begin. This should be done using a Hardwood bat mallet. This provides much better performance than a ball mallet, and the speeds up the process.
Start by hitting the middle of the bat just hard enough to create a dent. [This is surprisingly hard]. Hold the bat up to the light to see if you are making a dent.
Gradually compress the face of the bat around this dent so that the face of the bat is level and you cannot see the initial dent any more. The bottom of the bat toe (the part that is in contact with the ground) should never be hit with the mallet.
The edges require special attention; they need to be rounded off so that the hard new ball cannot damage them too much. The edges should be struck at 45 degrees to the face so that the mallet can compress the willow. Similar to the face make one dent on the edge, and then gradually even out the edge so that the whole surface has a smooth, rounded appearance. The back of the bat should never be touched with the mallet (or the ball). (that goes especially to Mr Hetherington)
If the bat is hit at 90 degrees to the face on the edge it reduces the width of the bat and is covering an area not mechanically pressed. The likelihood of cracking increases and you should not be hitting the ball flush on the edge in any case.
With a hardwood bat mallet the knocking in process should take from between 10 to 15 sessions of about 10 minutes each. Once you have completed this process, as a guide to see if the bat is ready for play take it into the nets and play a few shots with an old ball. If the bat is showing very deep seam marks to the point of almost cracking the face of the bat then it needs more compressing. One will always get seam marks on the face of the bat; they should not be too deep.
The price of a bat does not have any effect on whether a bat cracks or not. The best bats are usually more expensive, but liable to crack more than cheaper bats because the willow is often softer.