BLADES Writer's experience is on 48" deck blades shown. Thickness varies by tractor. Blades shown .200" thick! Perfect for grinding. Rust resistant, alloy steel. Too nice to keep replacing and they ain't cheap....Notice below the straight edge aligned against one blade depicting the material removed in 8-9 years of sharpening (about 1/4 to 3/8") . The heft of this blade is useful as a "heatsink" during grind, lessening worry about metal burn/softening. It is also relatively easy to hold against the grind stone with your (sensitive) bare hands . As new. the blades had "hollow ground" edges (think straight razor). These pretty edges are easy to sharpen and nice and narrow. They will disappear in several sharpening episodes, at which time you will be into the "thick" of it , .200" in this case . Hollow grinding is probably not for the home shop . If you sharpen wood planes or chisels you can sharpen these blades. :smile:
tutorial blade sharpening ,freehand grind
- Thread starter motoman
- Start date
SHARPENING We all know some fancy names for the various sharpening angles and probably know a lot of recommended angles. Not used here. If you grind a wide slope toward the edge of the blade and then grind a a decent edge the blade will CUT. No angles are therefore specified. Lets just say that too narrow an edge will not hold up as well , and too thick an edge will not cut as well. The cutting edge should be a narrow band ( say 1/16 to 1/8"). Back of it going uphill to the blade body thickness is a slope. I would like 1/2", but usually don"t make it (lazy?) The 3 blades shown have about 3/8". You will do heavy grinding to keep moving the slope slightly back to accomodate the new edge you create. Sometimes just a touch up on the edge is enough. Large nicks are not a problem here, only mole hills , weeds and grass. I think I would sharpen over deep nicks If I had them, to preserve blade material. They will eventually disappear.:thumbsup:
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The H-Frt motor used is 3/4 hp, not 1/2. Author correction Motoman
It's the 2 way tool I mentioned above. The sketch and dims are provided below. I originally made it to break the 100 ft lb flywheel nut loose and somehow pressed into service pulling blades. Country people may recognize the red metal as a fence post "arrow," and car people may recognize the blue as an extra hydraulic jack handle. A real simple, low cost tool that WORKS.
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FREEHAND GRINDING This means no jigs, or guides, just your feel and judgement. You all have it or can develop it. Practice on an old blade or even mild steel sheet if you want. Be as careful as you can with the blades, but I have found them forgiving .
TAPER Either final edge or the larger taper can be done first. It seems easier to start with taper. Hold the grinding side of the blade to the wheel at an angle (pic) You may find another way, but horizontal seems to encourage a notch at the end of the grinding passes near the center ( see "R" with semicircle in bluing on previous blade pics). Notches provide a weak area for cracks. Rotate the cutting edge toward you (top edge) so the wheel meets the taper area . An air gap shoulld be seen between the cutting edge and the wheel which must be maintained while grinding the taper. (...do not grind the final edge now). Start grinding at the end and moving up the blade toward the center . At the radius reduce pressure. If confident , rotate the blade slightly , (maintain the air gap), and start toward the end. If unsure , lift blade and inspect grinding path. Start over. After confidence is reached you will be able to make numerous heavy passes and reduce the .200" to a slope of your choosing. A taper pass with my beast takes 4-5 seconds, no burning. Keep wheel clean ( below). Swap blade ends and apply same number of passes and pressure . Keep blade moving.
TAPER Either final edge or the larger taper can be done first. It seems easier to start with taper. Hold the grinding side of the blade to the wheel at an angle (pic) You may find another way, but horizontal seems to encourage a notch at the end of the grinding passes near the center ( see "R" with semicircle in bluing on previous blade pics). Notches provide a weak area for cracks. Rotate the cutting edge toward you (top edge) so the wheel meets the taper area . An air gap shoulld be seen between the cutting edge and the wheel which must be maintained while grinding the taper. (...do not grind the final edge now). Start grinding at the end and moving up the blade toward the center . At the radius reduce pressure. If confident , rotate the blade slightly , (maintain the air gap), and start toward the end. If unsure , lift blade and inspect grinding path. Start over. After confidence is reached you will be able to make numerous heavy passes and reduce the .200" to a slope of your choosing. A taper pass with my beast takes 4-5 seconds, no burning. Keep wheel clean ( below). Swap blade ends and apply same number of passes and pressure . Keep blade moving.
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CUTTING EDGE Rotate the blade edge (top) away from you toward the wheel, eliminating the air gap. With lighter pressure than on the taper , grind toward center. Again try to finish the pass with a gentle radius rather than a notch. Feel the backside of the blade for a burr or "wire." If detected, and if you are satisfied with the cutting edge width, stop. If no burr you probably have not completed the cutting edge. Rotate the cutting edge a little further onto the wheel and repeat. You should not burn with this gentle pass ( and you keep moving , right?). Putting on the final cutting edge can be done on a finer grit wheel if you have one ( say 80 grit). You will get a smoother edge which may hold up a little better. Under magnification however , all edges look sawthooth . Finer grit wheels are more prone to burn. Just kiss the edge. Remove the wire backside with flat strokes from a mill file (flat, no angle). The first pic below shows cutting edge blued. The 4th pic below has slope blued to show the ground cutting edge. Total one way grind pass duration is about 3 seconds ( you are not presssuring the blade nearly as much as on slope )
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I use a 36 grit stone & a fine stone just to take off the lip on the back side. Follow the angle on the blade. If the angle is gone, time to chuck the blade. The 36 grit removes the metal faster and doesn't heat the blade so much. If I have some real heavy blades to sharpen, I will dip the blade in water every so often to avoid overheating. I also use a magna matic blade balancer. It also has a rod attached to the balancer to check if the blade is bent. If the blade isn't too bad, I use a 4 1/2 grinder with the blade in a vise. That works well on some of those odd shaped curved mulching blades.