The blades are dull when the grass is not getting cut effectively. This is evident when after passing over an area there remain patches of uncut grass. Also you may find some increased resistance, especially if you are using a simple push mower.
No how often they will need sharpened will depend on how much you use them and what on.
u speaking of skates? 6 ,months
The blades on riding lawn mowers spin due to the power generated by the engine. When the engine runs, it drives a belt or a direct connection to the blades, causing them to rotate at high speeds. The spinning blades cut the grass as the mower moves forward, ensuring an even and efficient lawn trim. The speed and height of the cut can often be adjusted based on the mower's design.
Every 25 Hours of use.
Air is fine, fuel is required, but air is often there as well
The amount of time in between sharpenings will depend on the complexity and frequency of use. If the knives are used heavily it will need sharpened more frequently. If the knife has trouble cutting through the appropriate item then it will need sharpened. Most knifes in a kitchen where they are used frequently will need sharpened every 2-3 months.
Every time you start to have the lubrication strip turn white it is time to change the blades.
As your mower ages and starts to show signs of a lot of use, the mower blades will often wear and become what is known as rounded. This rounding of the blades causes there to be a slight gap between where the blades would normally meet up and cut the grass, causing them to miss a small patch of grass in the middle. The best solution is to replace your mowers blades.
A snow plow blade should be sharpened after every 50-60 hours of use, or whenever you notice reduced cutting efficiency. Regular sharpening helps maintain the effectiveness of the blade in clearing snow.
You should only sharpen your knives once per year, because after a while of continuous sharpening your knive blade will become thin.
Electric razor blades should be changed once every 12 months, but that could depend on the model of the razor. Changing razor blades properly will ensure an even shave.
Experts say windshield wiper blades should be replaced every six to twelve months, and wiper blade manufacturers recommend changing wiper blades every year.