referring to the drawings , the skid plate 10 has an upwardly - inclined front portion 11 providing a configuration similar to a ski or toboggan . a coupling structure 12 at the front extremity of the skid plate provides for the laterally - spaced connecting points 13 - 14 , and for a central and somewhat elevated connecting point at 15 . these points are positioned to receive the standard equipment on tractors for handling various implements . a diagonal brace 16 stabilizes the structure 12 to resist the forces involved . these members can either be welded directly to the skid plate 11 , or bolted to tabs ( as shown ) that are welded in position . a pair of roll brackets 17 - 18 are positioned on a transverse axis in opposite relationship , and are welded at the lower extremities to the skid plate 10 . each of these brackets is provided with a u - shaped receptacle as shown at 19 and 20 for receiving the tube 21 carrying the roll of film indicated at 22 . the tube is thus easily removeable for the installation of film rolls . locating collars as shown at 23 and 24 are slideably received on the tube 21 , and are secured in place by t - headed screws 25 and 26 so that the radial pins 27a - b and 28a - b can engage the ends of the roll 22 for confinement against axial movement . the film sheet , as it pulls free of the roll , is indicated in the drawings at 29 . as the film sheet 29 pays out past the rear edge of the skid plate 10 , it encounters the pressure roller 30 , which presses it down firmly against the ground . normally , the cultivated condition of the ground will leave it somewhat porous , the initial ground level being indicated at 31 in fig2 . as the pressure roller 30 becomes effective , however , the ground becomes compacted slightly under the film as the film is deposited . this new ground level is indicated at 32 . the pressure roller 30 is mounted with a limited degree of vertical movement , as a result of being carried by the laterally - spaced arms 33 - 34 , which are respectively pivotally connected to the roll brackets 17 and 18 as shown at 35 and 36 . the roller 30 is rotatable in the bearings 33a and 34a secured respectively to the arms 33 and 34 . the weight of the pressure roller will generate its own biasing action to produce the differential in ground level shown in fig2 . in fig3 the machine is shown in a preliminary condition , which permits the film sheet to be threaded underneath the pressure roller , and the machine is usually placed temporarily on a concrete surface for this purpose so that rests on the lower edge of the groove - forming devices 37 and 38 . to support the pressure roll 30 temporarily in the absence of ground pressure , the l - shaped supports as shown at 39 in fig2 can be swung from the fig2 position to the position appearing in fig3 . these supports are pivotally connected to the arms 33 and 34 as shown at 40 in fig2 and are rotated counterclockwise from the fig2 to the fig3 position . when the need to maintain the pressure roll 30 in an elevated position is no longer present , the moveable supports 39 are rotated back to the fig2 position . a pair of angular members shown at 41 and 42 are welded along their bottom edges to the skid plate 10 , and form supports for the rearwardly - extending cantilever arms 43 and 44 , which are bolted to the angle members as shown at 45 and 46 in fig2 . the opposite ends of a cross member 47 are bolted to the arms 43 and 44 as shown at 48 and 49 , so that the resulting u - shaped structure forms a cantilever frame extending to the rear of the skid plate 10 . a pair of links shown at 50 and 51 are pivotally connected to the arms 43 and 44 at 52 and 53 , respectively , and the rear extremity of these links carries a short tubular sleeve 54 and 55 welded to the links . end collars as shown at 56 and 57 surround the ends of the shaft 58 , which carry the film - depressing wheels 59 and 60 , with the wheels free to rotate on the shaft . locating collars as shown at 61 and 62 limit the movement of the wheels in a central direction , and the removeable spacing tubes 63 - 66 may be used in determining the correct front - rear alignment of the wheels with the groove - forming devices 37 and 38 . the rear ends of the links 50 and 51 are turned upwardly as shown at 67 and 68 to form terminals for the tension springs 69 and 70 which extend from these points to the cross member 47 . referring particularly to fig5 and 6 , the groove - forming devices are composite weldments which include a round bar 71 bent upwardly at the front end into parallelism with the forward portion 11 of the skid plate . the central web portion 72 welded to the top of the bar 71 bears against the underside of the inclined portion 11 . spaced parallel side plates 73 - 74 are separated to admit the lower portions of bolts as shown at 75 and 76 , which traverse suitable openings in the skid plate as shown at 77 - 80 in fig4 where they are engaged by nuts as shown at 81 and 82 and secure the groove - forming devices in position . a plurality of sets of these holes is provided , so that the spacing of the earth grooves can be selected as may be required , accompanied by the proper selection of the spacing tubes 63 - 66 for corresponding locations of the film - depressing wheels 59 and 60 . the principal function of the transverse rear frame member 47 is to provide support for the scraping blades 83 and 84 , which are secured to the cross member 47 by clamp assemblies 85 and 86 . the transverse member 47 is formed of two pieces 47a and 47b having an angular cross section , and separated by a slot 87 for receiving the clamping assemblies with freedom for lateral adjustment . these are properly located by experiment so that the scraped earth is deflected into the groove formed by the devices 37 and 38 , and into which the film 29 has been depressed by the wheels 59 and 60 . this final action secures the film in its installed position . the action of these scraper blades normally leaves a ridge of earth as shown at 32a in fig2 .
the machine is coupled to a standard tractor , and normally slides over the ground on a skid plate as the vehicle moves forward . a film roll is supported on the machine in a position to be unwound , and the film is progressively deposited on the ground behind the skid plate . groove - forming structure under the skid plate are disposed centrally inward from the edges of the film roll , and following wheels depress the edges of the film into the groove . scraper plates then move earth into the grooves , entrapping the edges of the film .