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Old November 1st 03, 02:27 PM
Roy
 
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Default Info on how to make a chipper knife

On 01 Nov 2003 06:36:33 GMT, (JWDoyleJr) wrote:

===
===Being that one of my knives on my chipper broke and I am a cheap son
===of a bi%#@ i need to make one. Its approximately 1.25" x 3.75" x .250"
===thick, with two 5/16" countersunk holes in it and a bevel of 37 deg
===ground on one long edge.
===
===
===Roy,
===I had a similar problem with a 10 HP Murray chipper-shredder. It had one
===blade, 1.375 X 3.125 X 1/4 with two 5/16 countersink holes and a similar bevel.
=== This was a shi**y design. The blade was too short to begin with, allowing a
===sliver of a green branch to slip by the inside end and wrap around the axle.
===It was also of the wrong material. The original blade fractured through a bolt
===hole, and a replacement was priced at about $24 + shipping cost.
===
===I went to the farm store and bought the cheapest plowshare in stock for about
===$7, and hacksawed out a blank and worked it from there -- mill, drill,
===countersink, grind. I made my blade 3.625 long, and it works like a charm. No
===fractures. No wraparound. And priced to please the cheapest son of a bi%#@
===on earth. After some experience, I tried grinding more "clearance" in my
===blade, and it literally sucks the branches in. (The original had to be force
===fed.) And I have a lifetime supply of material for more blades.
===
===Overall comment on this chipper: The chipper body and rotor do not have the
===strength to take 10 HP. I have about a pound of weld on mine, repairing over a
===foot of fatigue cracks and reattatching parts that were blown away. The
===rotating flails were mounted on weakened pins which failed, with results
===approximating an explosion.
===
===Try the plowshares for a source of cheap, tough steel. They're designed for
===fatigue strength and wear resistance. Milling it will test your skill and
===vocabulary. Say carbide, and then have fun.
===Pat



Yep, what you did is along the lines of what I was thinking, but I
used a heavy duty .300" thick mower blade tip that I acquired
somewhere. The blades on my JD mower seem to be holding a good edge
while used in sandy conditons, and are still pretty sharp, so thats
what led me to try a mower blade. Mine also broke off on one of thr
sections with a bolt hole, and the other section is cracked up to the
bolt hole and starting to propagate on the other side. I can see that
they need to be hard, but somehow I think they may be too hard, thus
making them fracture prone.

I like the idea of milling a step and brazing in some carbide........

I too am a cheap SOB (I did not get the name frugal machinist for
nothing, and have a hard time p[aying over $25.00 plus shipping and
handling for this small chipper knife, when I can vuy a 3" x 8" x
..375" thick knife for $22 that fits a commercial chipper unit. The
price just does not fit this item. If I had a way to cut and
countersink the bigger knife, it would be a item to make it out of as
well. Guess I will check the local farm supply for a plow share, as I
do know they are much harder than a lawn mower blade is.


Another thing I had considered was usuing z piece of this mower blade
and hard facing a couple of beads of hardface on it and then grinding
the edge, but that would propbably be more trouble than simply milling
a step and brazing in carbide, or milling out a plow share to fit.
Biggest problem is my countersink, but its doable.
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