Technical
Of equal importance, a reduced land on the blade can ensure the cylinder blade to bottom blade angles are more tightly controlled for a cleaner and more consistent cut.
A spin grind will typically need to be carried out more often as the cutting edge tends to dull sooner. As with backlapping, spin grinding delivers best results if carried out little and often. Regardless of technique adopted, the most important issue is to keep cylinders sharp. So spin grinding will always be preferred to running dull cylinders.
So relief is best?
Simple answer is yes. Manufacturers put a relief on the back or trailing edge of a blade for a reason. When this relief is worn away, it needs to be reinstated. So spin grinding can only work well as long as the original relief remains post sharpening. It may be the case on some commercial mowers that no relief is present. Conversely, if you want to retain the relief as per the manufacturer’s specification, you need to regrind it as it is eroded by blade wear.
Contact or air gap?
With regard to air gap versus light contact ‘reel to bedknife’ settings, it depends on who you talk to; Toro are in the light contact group, John Deere and Jacobsen setting most of their cutting units for golf with an air gap. As a rule, it is best practice to follow the advice offered by you equipment supplier.
What about backlapping?
Not everyone thinks backlapping is a good idea. The process re-hones the cylinder cutting edge from the rear and also possibly takes the cylinder ‘out of true’ as it relies on the action of a grinding paste between it and the bottom blade. Backlapping can actually further dull cutting units that are blunt to start with too.
The counter argument is that backlapping is not intended to resharpen a dull blade. Its job is to help retain an existing cutting edge, helping to restore it as it just starts to dull. Judicious ‘little and often’ backlapping can help lengthen the periods between regrinding the cylinder.
Accepting a manufacturer will always argue in favour of buying its products, the following may help those considering grinding in-house.
Cost: The expenses related to sending cutting units out to be sharpened will range between £100 to £150 per unit. Some units may need to be ground more than once a year, due to ever increasing frequencies of topdressing applications hastening cylinder wear.
Quality of cut: In-house grinding can help ensure units are kept in premium condition throughout the whole of the cutting season - around 80% of grinding work with third parties is carried out over winter. Owning your own machine enables grinding schedules to be timed around topdressing programmes, weather patterns and competitions.
Quality of grind: Golf courses operating their own grinding equipment will not face the same pressure to work to grind large numbers of units, this in turn allowing - it is hoped - for more time to be dedicated to the grinding process. Automatic grinders are offered. These make it easier to maintain repeatedly high levels of grinding
performance. With your own grinder, you are in charge of your own quality control.
Some points to consider when choosing a grinder
Enough setting to suit the job: a key requirement is to ensure the grinder under consideration will return both cylinders and bottom blades to the original manufacturer’s specification.
Accuracy and durability: The grinder should perform accurately for at least a decade. When costing a unit, find out the machine’s maintenance demands and its projected service life. Compare machine specifications and ensure the unit will work to the tolerances you demand and that these are easily achieved.
Coping with coning: Some modern cutting units have the cylinder and rear roller fixed in the frame during manufacture. During use, the cylinder can be subject to ‘coning’ that cannot be corrected other than through correct grinding. Check the machine you purchase will be able to remove such coning.
With thanks to Hunter Grinders - a division of Lloyds & Co of Letchworth Ltd.
The problem with backlapping is that not everyone understands that it is only effective if the units have been relief ground, because the relief is necessary to force the paste to the cutting edge. It is not just a case of slapping on some backlapping compound, winding on a little extra pressure on the bottom blade and then running the cylinder up to speed in reverse. The job needs to be carried out according to the mower manufacturer’s instructions and performed long before the blades on the cylinder are really dull.
There are those who actually advocate a modest backlap post grinding; the argument is that grinding leaves a burr on the cylinder blades and backlapping removes them. The more widely accepted consensus is that any burrs quickly dislodge during initial mowing, making a backlap unnecessary.
What about the bottom blade?
The correct bottom blade ‘shear’ angle is absolutely critical to the performance of the cutting unit. The sharpest cylinders will not deliver if they are acting on a dull or incorrectly profiled bottom blade. So it follows that grinding the bottom blade is as important as honing the cylinders. Bottom blades also have a finite life, with a wear limit mark cast into many OEM designs.
What the OEMs reckon
All the major manufacturers of precision grinding equipment offer machines or accessories which allow the operator to choose between spin and relief grinding, but only a couple offer both options combined in one machine.
On the recommendation of some manufacturers, such as John Deere and Jacobson, units should be set up to have no contact between the reel and the bed knife.
Other manufacturers, including Toro, suggest that the set up should ideally have very light contact between the reel and bed knife.
The reel back relief angle on John Deere equipment is ground to remove the cross section of the blade, leaving approximately 1mm. This angle is set at 20 degrees, although the industry ranges from 20-45 degrees.
“John Deere recommends relief grinding the cylinders for many reasons,” says the company’s Technical Support Specialist Ivan Miller. “Relief grinding removes metal from the trailing edge of the blade forming a relief angle to reduce the blade cutting area (land) that is in contact with the grass, and this, in turn, results in less friction between the reel, grass and bedknife.”
“Relief grinding also extends life and sharpness for both reels and bedknives. By remaining sharp for longer it eliminates squeezing and tearing of the grass.”
“Another advantage of applying relief to the blades is a direct saving on fuel and repair costs. These will go up when reels get dull, or when there is no relief grind, because it does take more engine horsepower to spin the reels and that power will wear out components sooner. With relief ground blades less horsepower is required to drive the cylinder.”
Dan Dubas from the Turf Division of Lely UK also has strong arguments for their Toro professional mowers having relief on the blades, although they advocate different angles on the bedknives in keeping with their policy of light contact rather than non-contact mowing.
“Our reasons for relief are well documented” he comments. “We have found very strong evidence to support that relief is responsible for a reduction in wear, a reduction in power requirement and an improvement in the quality of cut - due to a better, cleaner cutting action.”
“In addition, there is an increased recovery rate of the turf due to the clean cut of the grass leaf and improved machine life due to the reduced stress on the component parts.”
“It is vital, when servicing, to keep the machine operating as the manufacturer intended. Therefore, important consideration should be given not only to the method of grinding but also to using genuine original manufacturers parts so that the equipment is kept to the original manufacturer’s specification.”
“We certainly wouldn’t put an extra
expensive process in the manufacturing if it wasn’t a fundamental requirement.”
PC OCTOBER/NOVEMBER 2015 I 131
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