Is it a scythe or scissor cut?

There has been a great deal of discussion about a "scythe cut" versus a "scissor cut", and fact is that both work and both can be used to define how a bedknife is adjusted to the reel.

A "Scythe Cut" describes the practice of setting the bedknife to reel gap at more than .003 - .004" so there is never any "operational contact" between the reel and the bedknife. This adjustment setting works as long as the reel blades and bedknife are very sharp.

The "Scissors Cut" is the practice of setting the reels in one of a few methods that result, or can result, in a light operational contact. These methods would be setting with light contact or setting with .001-.003 clearance, depending on the manufacturer of the cutting unit.

The data below is from an Iowa State study that illustrates why Toro specifies and prefers to have the reel and bedknife set with "light contact" during the cutting process:

  Visual
Quality
Mowing
Injury
Chlorophyll
Content
Ethylene
Production

SHARP with "LIGHT" Contact 8.68 0.83 17.46 0.541
SHARP with “NO” Contact 8.20 1.85 15.73 0.593
DULL with “LIGHT” Contact 8.41 1.28 17.12 0.603
DULL with “NO” Contact 8.07 2.35 16.34 0.669

 

In Depth Look

The results shown in Figures 1, 2, 3, and 4 can be found in all four plots with the sharpness and adjustment settings described above, but the clean cut in Figure 1 was most prevalent in the “sharp with light contact” plot. Of more significance is a “dull with light contact” setting produced better results than a “sharp with no contact” setting.

While setting the cutting units with light contact may work best for one manufacturing design criteria, it does not mean that overall results will be the same for the engineering criteria of a different manufacturer.

The manufacturers who advocate clearance have engineered and designed their product where cut quality is best when a .001” to .002” gap is set for their cutting units. Anything more than this recommended gap setting can pull and tear the grass and have adverse effects to cut quality.

Anything tighter is not the optimal setting - have you ever considered how small of an amount that .001” to .002” is across an 18 to 30 inch span? These same manufacturers understand that when the cutting units are on the turf and put into operation, it is possible to have light operational contact. If this occurs with their preferred setting, it is acceptable providing the reel specifications have been adhered to.

As a grinder manufacturer, it’s not our position to tell you how to adjust your reels, as we leave that to the OEMs such as Jacobsen, John Deere and Toro. So listen to your OEMs - if there were better recommendations that would allow their equipment to function better, they would be using those methods.

 
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