Sports Turf Research Institute Report Grinding out the benefits: Examining the cutting edge of mower maintenance. Mowing is the single most important maintenance procedure that is conducted on amenity turf. With this in mind it follows that the mowers used should be kept in good order. A wellserviced mower will have a longer, healthier life and a mower with a sharp cutting unit will produce healthier turf. ‘Cleanness of cut’ can have a dramatic effect on turf health. Turf cut with a blunt mower will have a reduced resistance to stresses such as drought, cold, wear from play and turf disease. The visual quality of the turf will also suffer. Badly cut turf displays a white sheen. On close inspection this is ‘ripped’ or ‘ragged’ leaf blades. Rather than being cut cleanly the turf has been ‘ripped’. Grass becomes caught between the reel (cylinder) and bedknife (bottom blade) and because the unit is not sharp, the blades are pulled and torn rather than simply being cut on contact. This can be compared to the finished edge on a piece of paper that has been ripped by hand rather than cut with a sharp pair of scissors. Playing quality also deteriorates as the health of the turf suffers. Ball roll and bounce are both affected on poor quality turf. In comparison to this a mower with a sharp cutting unit will cut the leaf blades ‘cleanly’, the turf will look good, be more resistant to the stresses that are imposed on it and maintain good playing quality. Clearly it is vital that lawnmowers are kept sharp, but what is the best way to do this? Within the amenity turf industry there are two distinct methods used to maintain the sharpness of reel and bedknife. The first technique is the traditional method of ‘lapping’ or ‘back lapping’. This method requires light contact between reel and bedknife at all times to produce a clean cut. This technique causes dulling of the two edges and without frequent ‘back lapping’ will result in an inferior cut. To maintain the tolerance between reel and bedknife the cutting unit requires infrequent sharpening (grinding), but regular ‘back lapping’. The ‘back lapping’ process consists of spinning the reel in reverse whilst applying an abrasive paste to true up the wearing surfaces. The second method is ‘non lapped’ or ‘non contact’. As the name suggests this method requires clearance between reel and bedknife so that there is no contact between the two. In this set up there should be a gap between reel and bedknife, typically the thickness of a sheet of paper. This technique imposes less wear on the mower blades as the wearing process is caused purely by contact with the grass and top dressing material rather than the ‘metal to metal’ contact required for the ‘back lapping’ technique. To maintain sharpness the cutting unit (reel and bedknife) should be ground every thirty days. Also the bedknife can be sharpened regularly with a portable front face (bedknife) sharpening device known as a ‘rapid facer’. This device is magnetically attached to the bedknife and is designed to restore the front face of the bedknife to the original grind angle.
In the summer of 2006 Bernhards and Company Ltd approached the STRI with a view to conducting some trial work to investigate differences between the two methods of maintaining mower sharpness. Bernhard and Company is a major manufacturer of grinding systems for mowers. Their products are sold to many leading golf clubs around the world. Bernhards put forward the theory that mowers maintained with the ‘non contact’ method using their products would produce better quality turf than mowers set up using the ‘back lapping’ technique. To investigate this a year long study was set up at the STRI. The trial was conducted on an area of fine turf dominated by bentgrasses and annual meadowgrass, typical of a UK golf green. The trial was laid out in a randomised design with twenty plots, ten plots for each mower treatment. Two identical Ransomes GS 55 Greens mowers were used. The first mower was maintained using the ‘back lapping’ technique. The second mower was maintained using the ‘non contact’ regime advocated by Bernhards. In order to maintain the ‘non contact’ mower Bernhards provided a Express dual and Anglemaster grinding system along with a rapid facer for routine sharpening of the bedknife. Both mower treatments were set up and maintained by STRI’s expert groundsmen and the trial area was subjected to the treatments for just over a year. Summarised results are presented in figures 1 3. These show that boldness and longevity of striping and visual quality (VM) were improved in the ‘non contact’ treatment. The ‘non contact’ treatment was also less susceptible to disease. Figure 2 shows that the ‘non contact’ treatment had a significantly faster rate of regrowth, or that the ‘back lapped’ mower, despite being set to the same cutting height, was cutting closer to the ground. Figure 3 shows that the turf colour of the ‘non contact’ plots was a little greener, an indication of slightly better turf health. 8 7
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Figure 1: Summarised Assessment Results (1 – 9 scale). BL: Back Lapped.
NC: NonContact. Sward Heights (cm) 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0.82 0.80 BL
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Figure 2: Sward height measured with rising disc apparatus. Colour 116.4 116.3 116.2 116.1 116.0 115.9 115.8 115.7 115.6 115.5 115.4 BL
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Figure 3: Turf colour (Hue angle; larger numbers = darker green) measured with Minolta Chromameter. The trial work suggests that maintaining mower sharpness under the ‘non contact’ regime can produce superior turf. However this is not the only consideration that a turf manager has to take into account when choosing a sharpening regime for his fleet of mowers. Time and money are factors that should be considered. The STRI Groundstaff felt that in terms of time spent maintaining the two mowers there was initially very little difference between the two treatments. Routine ‘back lapping’ took approximately half an hour and routine front facing took five minutes. Monthly grinding of the ‘non contact’ mower took less than an hour. The Express Dual grinder that sharpens the cylinder is extremely quick as the mower can be
ground ‘in situ’. The Anglemaster bedknife grinder is more time consuming, as the bedknife has to be removed from the mower. Maintenance time for using the grinding system was reduced as the groundstaff became more expert in its use. The STRI staff commented on how ‘user friendly’ the Express Dual and Anglemaster were, it took very little time for them to become accomplished operators. With regards to costs a system such as the Express Dual and Anglemaster would require a significant initial outlay. However, subsequent maintenance costs would be reduced as there would be no need to employ specialist grinding companies to re grind mowers on an annual basis. Maintenance costs could be further reduced in the long run as staff become proficient in the use of the grinders. Sharper mowers that produce better quality turf will also potentially save money by reducing any remedial action that has to be taken to solve problems. Healthier turf is naturally more resistant to diseases; therefore time and money should be saved by reducing chemical input. In conclusion, our study found that running mowers using the ‘non contact’ method of setting up the cutting units and using grinding to maintain sharpness was an improvement on the ‘back lapping ‘ method.
By Mark Ferguson