Ask the Mechanic
Safety Tip of the Month March 2025: Unbalanced Blade
Lawn mower blades usually run around 3,000 rpm, reaching speeds of around 18,000 feet per minute, or roughly 250 mph. The actual mph speed can only be derived from the radius of the blade and the actual rpm. However, these numbers represent a big danger when the lawn mower blade is not balanced. The faster something is rotating, the more crucial the balance becomes to eliminate vibration.
The lawn mower blade shown (see photo accompanying this article) was one of a set of three blades that came to my shop to be sharpened. This is absolutely the worst possible example of blade sharpening that I have ever seen. Never weld on a lawn mower blade. Even after sharpening, the blade should always be balanced.
Note: The guy who brought these lawn mower blades to be sharpened did, in fact, tell me the mower was not cutting cleanly and had a terrible vibration in the deck.
You've got to be kidding me.
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-- Email Steve Thompson care of askthemechaniccolumn@gmail.com, and be sure to include your contact information and phone number.
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