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NATIONAL 68" SR & DL TRIPLEX – CE
®
15
FIGURE G
INTRODUCTION
Back lapping is a very important step in maintaining sharp
reel blades on the rear and wing mowers.
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 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 bed knife to the reel so that the bed knife is
level with 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 manu-
facture.
FIGURE H
Many types of compounds are available for lapping.
However, we recommend a good pre-mixed water soluble
compound. Many different grit ranges are available. 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 course 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 Figure
I, Page 16) and repeat Step 3 untill 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
Adjustments, Page 16 for detailed instructions).
3. Apply the lapping compound with the reels running,
using a 2" or a 3" brush. Apply the compound evenly to the
moving blades.
Be extremely careful not to let the brush, your
fingers or your clothing get caught in the reels.
Use approved safety glasses to protect your
eyes from flying particles and abrasives.
GRINDING
Reels must be ground at 25° in the direction shown below
by the arrow in Figure G. 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 diam-
eter.
For maximum cutting efficiency, grind bed knife top and
front edges at 5° as shown in Figure H.
BACK GRIND IN THE
DIRECTION
OF THE ARROW AT 25
O
Note centerline
POSITION OF
REEL
TO THE BLADE
25
O
5
O
GRIND BED KNIFE
AT ANGLES SHOWN
5
O
LAPPING PROCEDURE