Maintaining cut quality between regrinds...
Nigel Church is a Product Trainer with Cutting Edge Training, an operating division of Ransomes Jacobsen. A well-known and highly respected figure within the industry for over 40 years, he began his career as an apprentice at Ransomes, Sims and Jefferies in 1970 and has worked in the UK and Europe. In this article, he looks at maintaining cut quality between regrinds.
In the last article, we looked at "how to extend the life of machinery, by adopting correct maintenance procedures". This month, we will be taking a look at how you can maintain a good quality of cut between regrinds on your cutting units.
Hopefully, your machinery is in peak condition at the start of each season. It is either a new machine, or a machine that has been fully serviced; as a part of that process, the cutting cylinders will have been spun ground to ensure they have been returned to a true cylinder, and the bottom blades will have been reground or replaced with a new set.
It is what you do now that will affect the performance of your cutting units until the next regrind.
The Environment
Cylinder mowers work in a wide variety of environments, and this of course has a considerable effect upon the condition of the unit.
Commercial Mowers
As well as avoiding the worst of the debris on the work site, the way that the cutting cylinder is adjusted is crucial to the number of hours the blades will last before they need to be replaced. The cylinder should be free turning, without drag from the bottom blade. If it is not, then precious hydraulic cutting power is being lost in forcing the cylinder to turn, and therefore there is less power left to cut grass with. In heavy growth conditions, very light contact is OK, as the lush grass will offer sufficient lubricant to keep the cylinder running without overheating. When the growth rate drops off, and the grass dries out, then the cylinder should run with a slight air gap between the cylinder and the bottom blade. This prevents friction and heat build-up, which will take the temper, or the hardness, out of the bottom blade and leave soft spots. Any blades which are damaged in this way will wear very quickly, and will need to be replaced frequently.
How do you set it with a slight air gap? Well, use a piece of paper like a feeler gauge to accurately set the gap. Office copier paper is rolled to a very accurate thickness (to avoid jamming when it's used in a printer or photocopier), so it's a uniform 3 to 4 thou" (0.1mm) which just happens to be the average thickness of annual meadow grass, so it's ideal for the job! You can also use the setting papers available from your manufacturer, as pictured. This sounds like a real fiddle but, if practised regularly, setting the cylinder correctly soon becomes second nature. The difference in the cutting quality is very noticeable, as is the increase in blade life, so it's really worth getting it right at the start of the season.
So, how long should a bottom blade last? Well, if correctly adjusted, a genuine bottom blade should last 300+ hours, or you should use two sets of bottom blades per season (on average). If set too tightly, then six sets of blades per season is not unheard of, but it is very poor practice, not to mention expensive!
The Cylinder
Of course, if you are wearing out several sets of bottom blades per season, the cylinder will also be seeing excessive wear, and they are much more expensive to replace than bottom blades. A 6k Magna cylinder should last two full seasons. If you screw the blades down tight, then you will have to replace the cylinders every year as well!
Get those blades up!
Every turn of the height of cut adjuster will raise the bottom blade off of the ground slightly more. The higher the blades are, the less they will contact the ground (scalping), and the less debris will travel between the bottom blade and the cylinder. Unless it is a sports playing surface, it does not need a close cut.
There is a common misconception that shaving the grass will mean that there is less on the next cut. This is simply not true. The grass will grow by the same amount every day until it's at least 12 inches high, so shaving it makes no difference to the amount of regrowth. The only thing achieved by low cutting is wearing out the bottom blades much quicker, and allowing more debris to get between them causing more wear, and more time lost in additional adjustments.
Fine Turf
The quality of cut on fine turf is a much higher priority than most commercial applications, so there will be more blades in the cylinder (to increase the clip rate), and thinner bottom blades to allow for a closer cut.
The adjustment of these cutting units is essential to its performance. The cylinder should always be running on an air gap of 2 to 3 thou" (0.1mm). Always use a piece of setting paper to accurately set the gap at either end of the cylinder, and don't forget to check the middle as well.
Roller adjustment
If you have floating headed units with front and rear rollers, always check that they are parallel with the bottom blade (it's essential for an even, level cut), and check that the angle of the bottom blade is correct. It is too easy to adjust only the front roller on some units, and this can change the pitch of the bottom blade, making a superior quality of cut impossible, regardless of the condition of the blades.
Always check the operator's instruction book when changing mowing heights, so that you set the front and rear rollers correctly every time.
Topdressing
There is a lot of essential renovation work in spring, however, running sand through the units will do nothing for the quality of cut or for the quality of the turf you try to cut with badly worn blades. If you have topdressed, then turn the irrigation system on to water it in, and leave mowing for as long as you can to allow the surface to settle before attempting to cut. If possible, roll the surface (with some accessory units) instead of cutting it for a day or so. You have spent time, effort and money getting that sand down, so why fill the grass box up with it the following morning, unless you really have to!
Backlapping
Regardless of how well you adjust the units, they will eventually "go off". When the cutting edges are dull, grass is pulled and torn, instead of cleanly cut. For fine turf applications this is unacceptable, and the decision must be made whether to backlap onsite, or perhaps send a vital piece of mowing equipment off to the dealers for a regrind, if you do not have grinding facilities on-site.
Backlapping is often a forgotten, or sometimes overlooked way of sharpening dull blades. There can be serious safety concerns with applying grinding paste to a fast turning cylinder so, instead of risking an accident, why not apply the paste to the cylinder before driving it? That way the job can be done safely. You'll need some cardboard or similar material under the unit as the paste will go everywhere, but, after a few minutes, you can stop the cylinder and inspect the newly ground surfaces. If any part of the cylinder is still bright and shiny, then it has not been ground and the process should be repeated. If you cannot rectify the cut within a few minutes, then it's probably time to regrind the whole unit.
So, to retain the quality of cut between grinding it is essential that the cutting units are carefully set, and the setting is checked and reset throughout the working day. On commercial mowers, the height should be as high as possible to minimise damage, and wear and tear; whilst, on fine turf machinery, the height of cut should be checked to ensure that it is correctly set for the bottom blade pitch angle, and for a smooth, even and level cut across the whole width, which could be 7 units on a big fairway mower.
Setting units correctly is not a difficult task; it is just a discipline which must be learned. If you are unsure, then get some training on cutting unit adjustment and setting from your supplier or the manufacturer. The cost savings, and the improvement in the quality of cut, really will make all the difference.