National Mower 68 DL Back Lapping Procedure, Introduction, Recommended Steps, Grinding Reels

BACK LAPPING PROCEDURE

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).

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NATIONAL 68 SR & DL TRIPLEX

BACK GRIND IN THE

DIRECTION

OF THE ARROW

25O

Note position of

blades to reel

axis

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.

5O

5O

GRINDING BED KNIVES

For maximum cutting efficiency, grind bed knife top and front edges at 5° as shown in the figure.