National Mower SR 68, DL 68 owner manual Introduction, Recommended Steps

NATIONAL® 68" SR & DL TRIPLEX – CE

LAPPING PROCEDURE

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.

3.Apply the lapping compound with the reels running, using a 2" or a 3" brush. Apply the compound evenly to the moving blades.

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).

BACK GRIND IN THE

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

DIRECTION

OF THE ARROW AT 25O

25O

FIGURE G

Note centerline

POSITION OF

REEL

TO THE BLADE

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.

GRIND BED KNIFE

AT ANGLES SHOWN

5O

5O

FIGURE H

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