on command the air cylinder will fill causing its piston to drop bars 77 and 78 into contact with the work piece to hold them down against the force of springs 55 and 80 during the tightening operation fig3 shows the mounting of the cylindrical bars 77 and 78 to the air cylinder 46 another air cylinder 88 is provided which drives a lead flattening shoe or cylindrical bar 86 this lead bar is actuated by air cylinder 88 and is connected by forward and rear springs 81 as shown in fig5 and 56 respectively it has a pivot 91 in the same manner as hold down bars 77 and 78 are connected to the air cylinder by pivot 90 both air cylinders 46 and 88 are actuated from the same air line 30 at the same time lead flattening shoe 86 is located approximately four inches from the forward flattening shoe 78 of the pair 77 78 the purpose of the lead flattening shoe is to hold down and align the wood in the next location to be flattened as well as to make sure that the wood is properly flattened by hold down bars or shoes 77 and 78 note that forward and rear spring 80 and 55 are.