chain saw cylinder to produce a lifting force of about 3000 8800 kgf 6600 19360 1bf depending upon the size of the cushion the size of the cushion is adaptable to suit the chain saw engine capacity and the type of trees to be felled or the type of wood to be split the invention also in its remaining parts can be varied in several respects in which connection for example the form of the cushion can be varied as desired for sawing of so called pointed timber for example the cushion suitably may be given a triangular or parallel trapezoidal form the device for drawing gas pressure from the cylinder may also be varied for example by positioning the check valve in the cylinder head and a three way valve in the passage between the check valve and the cushion the embodiment shown in fig6 however has the advantage that the high temperature in the cylinder does not act directly on the check valve and the associated spring when gas is not drawn from the cylinder the spring bias of the check valve of fig6 may be omitted whereby among other things a higher pressure in the cushion can be obtained a flexible casing for the cushion offers the advantage of good engagement with any uneven cuttings surfaces the cushion however if desired can be provided with a sheet metal lining on the upper and lower surfaces thereof or only on one of these surfaces this metal sheet may be grooved or provided with other means for effecting good engagement with the associated cutting surface in the tree trunk the term cushion in this connection.