It’s More Than a Grind: Part Two

Recapping of last month’s article, the fall aerification is complete and the mowers have gone through their last few mowing’s of the season. The reels are dull and bed knives are worn down to a knives edge.

Just as a reminder, be sure to remember how those worn reels and bed knives can be very sharp. I carry a prominent scar across the width of my right middle finger, from nearly cutting it off many years ago while washing and spinning a real by hand. Before I knew it I caught my finger between the turning reel and bed knife. It took a few years to regain feeling in the end of that finger. Not to mention my left hand has few scars from coming in contact with the grinding stone of reel grinder. These scars remind me of the scene in the movie “Jaws”, where the characters are sitting around comparing their scars. I am sure as Equipment Technicians, we can tell similar stories about our scars. Let’s try not to create any new stories. Take the time while working on this equipment to be very conscious of the dangers. Please don’t forget to wear your safety glasses.

This month I would like to cover a little more on the importance of the overall condition of the cutting reel and bed knife. The reel and bed knife are the major components of a cutting unit. A new bed knife has hardened machined steel that makes up the top and the front face of the cutting edge. This hardened steel material wears away from the action of cutting the grass, topdressing, back lapping and also overtightening of the reel to bed knife contact. With all these factors involved, the bed knife is a wear item and is replaced on a regular basis. This replacement can be many times during a mowing season.

The hardened steel cutting material of the reel blades are subject to the same wear conditions as the bed knife. But, the reel is expected to last for many years before needing to be replaced. Reels are generally replaced when the reel diameter becomes too small to maintain the proper height of cut. As the reel diameter decreases, so do the bed knife attitude and the adequate clearance between the bottom of the bed knife and turf. Bed knife thickness is also an important factor. A thicker knife is desired for longer life and lower budget cost. While at the same time a thin knife provides clearance between the bottom of the bed knife and the turf. Reduced clearance will allow the bed knife to drag the turf and cause unsightly after the cut appearance and raise the effective mowing height of cut. In some cases, the pressure put on the bottom bed knife will cause rifling of the reel and bed knife. Rifling creates heavy and light contact across the length reel and bed knife in wave pattern of highs and low spots in the cutting surface. The results cause’s streaked look to the finish cut of the turf. Rifling can only be corrected by grinding. No amount of back lapping will fix this condition. Another factor leading to reel replacement is bent or broken blades from an impact.

One very important step to take before grinding a reel is to measure the diameter. Every manufacturer has a specification for the minimum diameter of a reel before it needs to be replaced. One example is a new 5-inch diameter reel will have minimum wear limit of 4 ½ inches in diameter. It is waste of time and resources to grind a reel that is already too small in diameter, and in the final step of setting up your freshly sharpened and serviced cutting unit, you cannot set the low height of cut needed. At that point, you have to start over and replace the worn out reel. Another condition of the reel that has a very important impact on the cutting unit set up and after cut appearance is a tapered or cone shape reel. Tapered or coned shaped reel describes the condition of one end of the reel diameter being smaller or larger than the opposite end.

The reel is designed with twist or helix running the length of the reel blade from one end to another. So by design the diameter of the reel will begin to get smaller on the leading end that crosses the bed knife first during rotation. The taper will be increased even further when real to bed knife adjustment is more aggressive on one end or the other. For one OEM manufacturer, the maximum allowable taper for all reel diameters is .010 or about 1/64 of an inch. The golf greens average height of cut is .125 or 1/8 of an inch. With this average mowing height of cut, even with the allowable amount of taper can cause an uneven or mismatched cut between cutting units of a triplex mower and uneven cut between alternating cut directions with a walking mower. Some cutting units are designed and built with adjustments to accommodate some of this taper. The adjustment can be made at one end of the bed bar by an acentric or adjustable pivot point. This will allow an even reel to bed knife contact from one end to the other.

Reel diameter and taper can be measured with several different tools such a large caliper or a Pi diameter tape measure. The grinding equipment manufacturers also offer various setup gauges to achieve the result of putting a reel back into a cylinder shape again.

By taking the time to take a few measurements to verify the condition of the reel, you can set up the grinder accordingly. With little effort, you can produce cutting units that are easy to set up the reel to bed knife contact and will cut evenly across the putting surface. Good luck and happy grinding.