Go BottomMetal Stock to Fabricate a Mower Blade
 | auerbach
Join Date: Sep 2007 Posts: 2168 West of Toronto 
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2010-02-16 168658
Replacements for my MMM blades are unavailable so I make them. They're just quarter-inch stock, 7" X 2", with a 3/4" mounting hole at one end (two per spindle). But metallurgy is a mystery.
If there's such a thing as "blade" stock, what do I ask for at the metal store, and would there be a problem drilling the hole in it?
Do I just sharpen slowly to not heat it so much it loses its strength, or would I need water or oil dripping on it during the grinding?
Would an old leaf-spring be OK to use? Thanks.
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2010-02-16 168659
I don't think I could even begin to list all the reasons why this is such a bad idea!
Mower blades are forged and then tempered. Using 'regular' steel would result in a blade that tended to throw off little bits of steel every time it hot something.
That's if you were able to get them balanced enough that they didn't just fly out from under the mower completely.
I'd take one of the old blades to a farm dealer, it sounds like what you have is a rotary drum/disc (hay) mower blades in a finish mower, but those are usually no more than about 4" - 5" long.
If you have no other options but to 'make' your own, I would most strenuously recommend you at least start with the right beast. Get a mower blade for a regular push mower that at least is the right steel, with the correct size pilot hole and so on, then cut it down (using a band saw or hack saw to reduce heat) and resharpen it to the correct cutter shape.
BTW, if you have to use a grinder, try to use a 'wet' wheel, or a very large slow turning stone.
If you get stumped, send me an email with the make & model of your mower, I have lots of aftermarket sources to match up grass equipment parts.
Best of luck.
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| auerbach
Join Date: Sep 2007 Posts: 2168 West of Toronto
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2010-02-16 168664
Thanks for your thoughts, Murph, but I've used home-made replacements for decades with no problems except gradual wear (which I hoped to reduce if I used better metal). There's no way to balance them (except to ensure that the two that bolt onto the holders on each spindle are the same weight). Maybe they don't spin all that fast.
They look like grass-cutting blades except much thicker, ruling out starting with existing blades (not that I've seen similar dimensions or a round 3/4" hole). I've looked through many blade catalogues for any kind of starting point.
Three excellent Yanmar dealers say there aren't any more, but if you have other sources, Yanmar's part no. is KTR-172 (I'd need six) for the YQM-60 mower.
The only dimensions I didn't supply above are that the edges of the hole are 3/8" and 1 1/8" from the inner end. And the blades are sharpened along the outer half (the end opposite the hole) of the length.
To reword my original query, I go to a metal shop for a length of quarter-inch X two-inch stock of the strongest steel they have, and wondered if there were a better starting point. ....
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| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2010-02-16 168666
I think the center 'holder' as you call it (most manufacturers call it a "blade carrier") is the problem, it seems like your mower is a sort of half-breed machine, it is a finish cut mower with rough cut style blades on it.
There's lots of traditional blades, and I mean lots, of blades for 3pth and MMM finish cut decks that are 2" wide with a 0.755" hole in them. At that point you have only to cut them down and resharpen them.
I would say to get rid of the present blade carrier and swap it for one that fits your spindles and gives you the proper cutting width using common blades.
Best of luck. ....
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| auerbach
Join Date: Sep 2007 Posts: 2168 West of Toronto
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2010-02-16 168668
Can you tell me where I can find some of these blades?
Yes, I could replace the spindles with ones that take a traditional single blade (which I'd have to do anyway if a spindle failed).
As for replacing what Yanmar calls the "Rotor Shaft and Beam Assembly" (the holder is a clevis inside which the blade goes), it allows the blade to pivot around its mounting bolt so if it hits a rock it can swing back. You can't get that with a full-width blade. (May be why my blades last. They can swing through 180 degrees around their mounting bolt. The latter is 3/8" with a bushing to 3/4".)
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 | kthompson
Join Date: Oct 2005 Posts: 5275 South Carolina
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2010-02-16 168673
Auerbach, to begin with not saying any of this is safe. I looked at Oregon's site and they show a lot of 14 inch blades with center hole. Guess you might could buy a blade long enough you could cut the length you need and drill it.
It has been years back I worked with drill jigs. We use a steel called then "Tool Steel". It was easy to drill, grind or weld until harden. Then it made great drill bushings and would wear and wear and wear. Of course that means it was very hard so would be dangerous about breaking. You probably could find specs on it to harden it some for wear but not easy broken.
Also they do make a abrasive grade steel used in some things like buckets and other wear edges. It can be welded and I think drilled.
I understand Murph's concern and not taking anything away from it.
Have you tried the farm dealerships especially the hay guys to see if they happen to have blades that fit as Murph has suggested? Not sure of their size and could not find it but "Power Trac" uses blades along that design on one or some of their mowers. ....
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