Technical Cylinder grinding Relief or spin?
Despite the simplicity of methods employed in cylinder grinding, there remains a degree of confusion regarding spin and relief methods. What are the differences and do they matter?
I
t could be argued that those responsible for the sale of cylinder grinding equipment have made outlining what specific tools do far more complex than it needs to be. In very simple terms, modern golf course
mowers are designed to produce an exceptionally high quality of cut. This quality can only be maintained if the cylinders - or reels - are kept not only sharp but also maintained with the correct relief on the blade.
The relief is essentially a section of metal ground out behind the blade to reduce the actual width of the cylinder cutting edge. The relief helps reduce friction between the cylinder and bottom blade - or bedknife - where a cylinder is set to light contact. The relief also provides a degree of extra clearance behind the blade that, in turn, can help with the dispersal of clippings; this applies to cylinders set to both contact and air gap settings.
The relief cut into the blade essentially reduces the cutting edge width to around 1mm; this can vary according to manufacturer’s specifications and type of mower. Rough mowers, for example, may have a thicker cutting edge with
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a reduced relief. This is to ensure the cylinder cutting edge retains enough strength to cope with thicker, heavy mowing.
With a spin grind, there is no relief cut into the back of the blade, so the cutting edge presented to the grinder is simply reground. If the cylinder is relatively new, the existing relief on the back cylinder blade is likely to have sufficient ‘depth’ not to be ground off. So, although the spin grind will not have cut a relief, the existing relief may well remain and the cutting blade will still benefit from the relief.
Conversely, the relief is obviously eroded each time the cylinder is reground. So it follows that, once the relief is removed, it will need to be reground if the cylinder is to be returned to the manufacturer’s original specification.
Although this is a simplification, it follows that the relief essentially describes the edge of the cylinder blade where metal has been removed to reduce the width of the cutting edge.
Technical terms
The relief on the back of a blade is cut to a specific ‘relief angle’. The relief angle will typically be set by the mower manufacturer and will range between 20 to 45 degrees.
The cutting area of a given blade is often referred to as the land; so a blade with a relief that reduces the blade thickness to 1mm has a 1mm land.
Spin grinding
As the name suggests, spin grinding will typically sharpen the cutting edge and, assuming the grinder has been set up correctly,
restore the edge profile to its original angle to the manufacturer’s specification. The time it takes to do the job is influenced more by how long it takes to get the cutting unit into the grinder and correctly setting it up than the actual grinding process itself.
There are those who suggest a simple spin grind is always inferior to a relief/relief spin grind. This is a misleading argument because, as previously outlined, a relief may still be present following a spin grind.
Relief/Relief spin grinding
Terminology can be confusing, so it is best to consider relief grinding as a separate process; its job is to grind a relief into the back of the blade. If the blade cutting edge can be reground at the same time, then it follows that the job will be carried out faster and hence the somewhat confusing description of spin relief grinding; the grinding stones spin, but the cylinder blades are ground in turn - the cylinder is not powered and spun as it is when spin grinding.
Is a relief essential?
No, but it is true that relief ground units will always stay on cut longer than those spun ground only. Cylinders can be exclusively treated to a spin grind and still deliver decent performance. Manufacturer advice, however, tends to favour a relief grind for fine turf mowers, noting that, whether set up with or without contact, the technique reduces friction which, in turn, cuts heat generation which can help preserve the cutting edge for longer. Reduced friction also reduces overall wear and power consumption. The latter can help save fuel.
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