One of the principle reasons for our existence as a company is to produce equipment that cuts fine turfgrass with a sharp, clean and uniform appearance, whether this is a golf green at 2.5mm or a football pitch at 28mm. A considerable amount of time and effort goes into the design and manufacture of our cylinder cutting units, therefore it is crucial that the correct sharpening procedure is undertaken when it begins to wear.
Principally, this article is about cylinder grinding, but there are many other factors to consider which we will cover later. The main criteria, as far as our cutting cylinders are concerned, is that the original angles are maintained and cutting edges are left clean and precise.
There are three main types of grinding machines available:
• The cylinder remains in the cutting unit frame and has a spin grind (in situ), the bottom blade block is ground in a separate machine and the relief edge on the cylinder is ground on another machine
• The cylinder is removed from the cutting unit frame, has a spin and relief grind in the bearings of the cylinder grinder holders, the bottom blade is then ground by the same machine or a specialised blade grinder
• The relief and spin grind of the cylinder, bottom blade and groomer blade grind are carried out 'in situation' on one machine
Checks to be carried out before grinding is undertaken
Before attempting to sharpen cutting units, the following checks should be made. If any faults are found, they should be rectified before any grinding takes place; if not, the grinding will be inaccurate or the unit will go 'off cut' quicker during use. Also, anyone attempting to set up, operate, adjust or service any machine should be properly trained and warned of the dangers. Blades are designed to cut!
• Cylinder bearings must be checked. If there is any noise from the bearings after the bottom blade has been backed off, they must be replaced. If one unit on a mower is going off cut quicker than the others during use, then the bearings and seals must be changed. If you remove a bearing housing, and there is slight shading on the bearing outer, then they must be changed too
• The cylinder must not be conical or tapered or barrel shaped. On a greens unit, this can be checked by removing the front roller and placing a gauge bar (straight edge) under the cylinder blades and against the front face of the bottom blade. A feeler gauge can then be used to check for gaps or different widths each end. If the cylinder is found not to be parallel, then it must be ground back to a cylindrical shape (see diagram 1)
• All adjusters must be free from corrosion and functioning correctly
• Check that the cylinder and bottom blade have not reached their minimum service dimensions (these can be found in the operator's manual). As they wear, the geometry of the cutting unit changes dramatically, affecting the 'heights of cut' achievable and the aggression of the unit
• Check the cutting unit frame or chassis is square and all hardware is secure
• Check the correct thickness of blade is fitted for the desired height of cut
• When mounting new bottom blades, remove all rust and thoroughly clean the bottom block
• Ensure bare cylinders are mounted correctly in the grinder. They must be mounted the same way as in the cutting unit with cutting edge below the relief angle.
Cylinder and bottom blade angles
Diagram 2 shows one blade from a greens cylinder. It clearly shows the relief angle of 45O which is ground by a single blade grinder. It also shows the 'land' which is usually ground by the spin grinder and should measure 1mm.
Diagram 3 shows the front face angle. Generally, we recommend 5O on greens mowers and US built bottom blades. UK built blades should be 10-15O.
Diagram 4 shows the top face rear relief angle. All US built blades, except super tournament blades, should have a top face relief angle of 8-10O. Tournament blades (2.5mm height of cut) should have a top face relief angle of 5-7O, the same as UK built blades.
Note: When grinding bottom blades, coolant should be used to avoid 'hardening' or 'blueing' of the blade.
After grinding, all 'burrs' should be removed by a fine hone or block of wood.
Setting up the cutting unit after grinding
Generally, the cylinder to blade adjustment should be set up with an air gap to prevent heat build up, damage to the cylinder and longer periods between grinding. This is fine during dry, sparse conditions, and especially effective on greens mowers. High-quality grass, with a good moisture content at certain times of the year, will require a closer gap (near zero) to maintain the sharp, clean appearance that we all strive for.
Another important point to watch is the 'actual' height of cut compared to the 'bench set' height of cut. This can vary throughout the year depending on how much the cutting unit sinks into the sward. During wet periods, the actual height of cut can be 0.67 mm below the bench set height. When this happens, care must be taken to ensure the cutting unit does not cut below its designed height causing the blade to rub on the sward. This can cause the unit to go off cut quickly and can cause the unit to 'rifle'. A prism gauge can help you to see the actual height, and a solution is to raise the bench set height until the wet period is over. Different roller combinations can help, but a height change is a cheaper and easier solution.
This article has been our recommendations for sharpening cylinder cutting units. Other mower manufacturers and grinding machine manufacturers may have a different view, but hopefully it will help you set up your mowers to give the optimum cut on your fine turf.