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NATIONAL 68 SR & DL TRIPLEX
®
25
68OM-06/03
GRINDING REELS
Reels must be ground at 25° in the direction shown by the
arrow in the figure. Back grind until reel blades are free
from roundness, dents and nicks. Spin grind to remove all
burrs. All blades must be on the same diameter.
GRINDING BED KNIVES
For maximum cutting efficiency, grind bed knife top and
front edges at 5° as shown in the figure.
BACK LAPPING PROCEDURE
Be extremely careful not to let the
brush, your fingers or your clothing
get caught in the reels. Wear gloves to avoid cutting
fingers on sharp edges. Wear approved safety glasses
to protect your eyes from flying particles and abrasives.
INTRODUCTION
Back lapping is a very important step in maintaining sharp
reel blades on the cutting units.
This procedure should be performed when the reel blades
and the bed knife become slightly rounded and the grass
is not cut cleanly with only a slight reel to bed knife
adjustment. Also, after grinding the bed knife and reels,
you should back lap to establish a perfect match between
the bed knife and reel blades.
RECOMMENDED STEPS
1. Adjust the reel to the bed knife so that the bed knife is
parallel to the reel and light contact is maintained.
2. Reels must be run in a reverse direction to be lapped.
Remove the lower drive belts and attach a back
lapping machine (not supplied by National Mower) to
the reels. Follow the instructions furnished by the
machine manufacturer.
3. Apply the lapping compound with the reels running,
using a 2" or a 3" (5 - 7.5 cm) brush. Apply the
compound evenly to the moving blades.
Many types of compounds are available for lapping. We
recommend a good pre-mixed water soluble compound.
Pre-mixed compound saves the time required to mix,
eliminates the waste of abrasive, rinses off easily with
water and is available in all grit ranges from coarse to
extra fine.
4. Stop the reel and examine both bed knife and reel
blades to see that the cutting edges are uniformly
sharp. If not, gradually tighten the reel adjuster bolts
(see "Reel to Bed Knife Adjustment" above) and
repeat Step 3 until the proper sharpness results.
5. Rinse off the compound thoroughly with water to
remove all abrasive. Check for sharpness and readjust
the bed knife if necessary. Reel to bed knife contact
should be adjusted to easily cut a sheet of paper (see
"Reel to Bed Knife Adjustment" above).
BACK GRIND IN THE
DIRECTION
OF THE ARROW
Note position of
blades to reel
axis
25
O
DANGER
5
O
5
O