Should You Sharpen Or Replace Rotary Cutter Blades?

A rotary cutter, also known as a bush hog, is one of the best lawn mower options for tackling tall grass, weeds, and other out-of-control growths that desperately need to be reined in. With that said, this kind of operation will inevitably do a number on the cutter's blades. While replacement is definitely going to be necessary at some point, you don't have to go this route immediately. It's indeed possible to sharpen your rotary cutter blades, and better yet, you could likely handle this task yourself from the comfort of your garage.

When your blades look banged up and struggle to cut effectively, it's time for sharpening. With the blades removed — and eye and hand protection equipped — you will need a vise to hold the blade in position for sharpening. Once the blades are safely secured, you can sharpen them with an angle grinder using a 30- to 45-degree angle, as too sharp of an edge will scuff and break. Use the angle at the end of the cutting edge as a guide, following it along the length of the blade. In the end, both of your blades should be sharpened with even edges and within the same weight tolerance, keeping the weight distribution even across the cutter. 

Unfortunately, there will come a point when it is time to replace your mower's blades entirely. Since sharpening involves shaving down material and removing it from the blade, logic dictates that there will be a limit to rotary cutter blade sharpening. There are several telltale signs that replacement is the only way left to go. If the blade has been sharpened so much that it is too thin, it becomes a structural hazard. The last thing you need is a thin, breakable piece of metal hitting something hard while mowing, snapping, and flying off. This applies to blades that have deep, lengthy cracks as well, since this represents a clear structural failing that becomes a hazard.

Additionally, if the blade is bent or angled in some way, you should replace the blades instead of sharpening them. Not only will it fail to cut properly, but it could hit the deck or other cutter components. You shouldn't overlook the bolt hole either, since this is also prone to wear and tear over time. If it can't hold the blade effectively, you risk the blade wobbling and producing a poor cut at best, or the blade coming off of the cutter at worst. In any case, you're better off just buying and installing a replacement blade rather than taking any chances.