As shown in Fig. 2, there are three sets of the levers O¹, at the upper end of the expansion coils at the rear side thereof below the knife-bars E, one lever at each end of said bar and one in the middle thereof. As these levers act directly upon the under surface of the knife-bars E to raise the same I will call them knife-bar lifting-levers. There are also the same number of levers O^{6} at the lower end of the expansion coils below the cross-bar O^{5} projecting through to the forward side of the apparatus, as shown in Fig. 1. Rigidly secured to the cross-bar O^{4} is one end of a relatively heavy metallic expansion strip O^{8},--preferably formed of zinc--the lower end being secured to one end of the lever O^{6}; to the opposite end of the lever O^{6} is secured the lower end of a similar but longer zinc strip O^{9}, the upper end of the strip O^{9} being secured to the rear end of the lever O¹. As shown in Figs. 1 and 2, there are two of these strips O^{8} at the front and two of the strips O^{9} at the rear of the apparatus. In addition to the heavy strips O^{8}, O^{9}, there is provided at the front of the apparatus a heavy wide expansion sheet or strip O^{10}, which, at its upper end, is rigidly secured to the cross-bar O^{4}, and at its lower end to the front end of the middle one of the levers O^{6}. A similar heavy wide expansion sheet or strip O^{11} is secured, at its lower end, to the rear end of the middle lever O^{6}, and, at its upper end, to the middle one of the levers O¹. These heavy strips O^{8}, O^{9} and sheets O^{10}, O^{11} are preferably formed of zinc, and are not only capable of great expansion and contraction, but will be capable by their contraction of lifting the entire weight of the knife-bars E, with the carried balance-levers and expansion strips of expansion coils, the operation thereof being as follows: