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Lawnmower blade problem- can you help?

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My lawn mower's bottom cutter is straight until the load from resting it on the grass is applied. Then it bends, up at the middle, not at both ends and recovers when upward pressure is removed. This means that a perfectly well ground cylinder will either have to run with excessive clearance at both ends or interfere with the bottom blade around its centre point. What I did to overcome this problem was to file the cylinder so that it skims the bottom blade all the way along when the blade is resting on the grass. Well, not exactly this but its equivalent. I used a block of wood instead of grass. It meant filing away metal at the centre of the cylinder blades. This made the machine cut quite well. The only problem left is that about one inch at both of the ends of the cylinder interfere with something fixed as they rotate, making it impossible to get the full 14 inch cut advertised for this machine. I can't see or access this part very well. Does anyone else have this problem? If so how did you overcome it?

Edited by woolyhead

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Would a new bottom blade have been an option?

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Well, maybe. But the one I owned has bent as described so I rather thought a similar replacement would also bend. If I had access to a decent workshop I could make a bottom plate using gauge plate and harden it to stiffen it up. The bottom blade as it exists, slides along the grass in normal use. So it wouldn't be a good idea to make it much thicker than the original plate because that would definitely raise the height of the cut if the extra thickness was below the fixing plane and could make it collide with the rotor if it was too far above it. But there may be scope to thicken the lower blade slightly. But that wouldn't help with the other problem. ie interference between rotor's ends and somewhere on a stationary part of the machine. Has anyone any idea how to strengthen the lower blade so it all works together?

Edited by woolyhead

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The fixed blade of my Qualcast Concorde 35 electric mower has a trench worn into it by the rotary cutters. This creates a clatter as the cylinder of blades rotates and collides with the back edge of the trench. Cutting is supposed to occur at the front of the blades and after cutting there is supposed to be sufficient clearance between the blades to allow the rotary ones to miss the fixed blade, not cut a trench right along it from end to end. But the only way I can understand how the blades interfere in this way is if the lowest point of the rotary blades is behind the cutting edge of the fixed blade. There is no provision for bringing the rotary blade set forward, away from the trench. If I raise the rotary blades so as to miss the edge of the trench the mower fails to cut the grass. Can anyone advise me what's wrong with the setup please and how to correct it?

Edited by woolyhead

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Worth a chat with Alex at Dronfield Lawnmowers. Will probably ask you to take it in for a gander, so check their opening hours...

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Worth a chat with Alex at Dronfield Lawnmowers. Will probably ask you to take it in for a gander, so check their opening hours...

Thanks Riff Raff

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It turned out that the bottom blade had rivets at each end for holding it to the fixing brackets at each end and the rotary blades were hitting them. I reckon this means I need a new lower blade after all, truman. But for a different reason. Anyway, you were right. Thank you.

 

---------- Post added 25-06-2018 at 19:51 ----------

 

Just out of interest, the fixed blade on a reel type mower, that's to say one with a "cylinder" that rotates. The fixed blade passes a short distance over the ground and the rotary blades push the grass up against its front edge, just skimming over the fixed blade and thus cutting the grass. What is the ideal angle to put on the front edge of the fixed blade when the time comes to sharpen it?

Edited by woolyhead

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Ref my original post, it seems that the fixed blade needs to be ground on its top surface near the front but I can't find anyone who knows even the approximate angle to put on it nor how much of its frontal area to leave un ground. Opinions seem to vary between (i) don't grind at all but leave it at 90 degrees to its small front area (ii) 30 degrees relative to its base, leaving 2mm of front at 90 degrees. I'm beginning to suspect that either it doesn't matter and the mower works either way or nobody knows for sure.

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