through the drive coupling shaft 36 so that both drive shafts 27 27 39 are rotated at an equal speed referring to fig3 two eccentric wheels not shown are attached to each of the drive shafts 27 27 39 each eccentric wheel rotatably carries the large end portion 38 of a connecting member 37 the small end portions 39 of these connecting members are pivoted to pins 41 provided on beating bar supports 40 as shown in fig2 the beating bar supports 40 are slidably received by vertical guide grooves formed in guides 42 thus a pair of beating bar supports 40 as shown in fig3 are suspended at two points from corresponding eccentric wheels on both driving shafts 27 27 39 through the connecting members 37 and the pins 41 so as to be moved reciprocatingly in the vertical direction along the guides 42 as the drive shafts 27 27 39 are rotated to the lower surface of each beating bar support 40 are attached five beating bars 43 these bars 43 are disposed in side by side relation in vertical alignment with beating anvils 24 each of the beating bars 43 has two axially extending protrusions in its surface opposed to the beating anvil referring now to fig3 the drive shaft 27 is coupled at its left hand side end to a gear box 44 the gear box 44 accommodates gears by which the torque delivered by the drive shaft 27 is transmitted for driving the endless rubber base 26 through a shaft 45 which makes an angle of 90 u00b0 to the drive shaft 27 to the outer end of the shaft 45 supported by a bearing 46 attached is.