of the brush chassis 33 and includes a recessed groove 43 the recessed groove 43 receives and mates with the guide or flange 36 thereby the brush chassis 33 is cradled in the slot 42 and does not fall through the slot 42 when assembling or replacing one or more of the brush units 32 a 32 b 32 c and 32 d the brush chassis 33 can be easily slid in and out of its respective slot 42 via the opening as will be seen from the description provided below in the exemplary embodiment the brush units 32 a 32 b 32 c and 32 d of the set of brushes 30 a are locked into their respective slot 42 via the bracelet clamp 45 of the set of scrapers 40 a clamped to the top third section 26 likewise the brush units of the set of brushes 30 b are locked into their respective slot 42 u2032 via the bracelet clamp 45 of the set of scrapers 40 b referring still to fig1 and 13 since each set of scrapers 40 a and 40 b are identical only one such set of scrapers 40 a will be described in detail the.