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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 quite
well 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.
Below is data that came 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.
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Visual
Quality
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Mowing
Injury
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Chlorophyll
Content
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Ethylene
Production
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SHARP
with "LIGHT" Contact
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8.68
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0.83
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17.46
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0.541
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SHARP
with "NO" Contact
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8.20
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1.85
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15.73
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0.593
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DULL
with "LIGHT" Contact
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8.41
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1.28
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17.12
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0.603
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DULL
with "NO" Contact
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8.07
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2.35
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16.34
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0.669
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Pictures in figures 1,
2, 3, and 4 can be found in all four plots with
the sharpness and adjustment settings that are 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.
Listen to your OEM's - if there were better recommendations
that would allow their equipment to function better,
they would be using those methods.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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