Info on how to make a chipper knife

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.

For the time being I used a old but unused heavy duty mower blade which was as hard as a leaf spring is, and cut it to size and have been using it, but it does not quite hold up as good as the original blades did, but its still useable.

The original is supposedly hardened to 58 rc. So what materials would you recomend making this blade out of.? I don't really have a temp controlled furnace, but I maya be able to acccess one, unless I can get by on heating with a torch or in my crucible furnace.

Any info appreciated.

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Why not mill a step into a properly sized blank and braze in some carbide? You ain't making veneer so it could be a few smaller pieces brazed in. Only the edge needs to be hard.

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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

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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. Visit my website:

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I don't like the carbide idea as carbides are brittle and chip easily.

Not as cheap as me! ;-)

I would try the following: Cut the blade out of a piece of old (free) leaf spring (plasma or O/A). Anneal, flatten, drill the holes and roughly shape the edge. Build up the edge with Stellite #6 (TIG or O/A). Grind the edge to finished shape and sharpen. You can then harden and temper to purple for additional strength if you wish. The heat won't affect the Stellite. You may have to sharpen it once after some use as the Stellite work hardens.

BTW, I picked up a box of Stellite #6 TIG rods at a blow out sale at the local welding shop. Stuff is expensive but that knife wouldn't take even half a rod. I've made center punches for hot work out of tipped re-bar scrap and even used it for some heat resistant electrical contacts. Well worth having a few rods around.

I loaned a friend a cold chisel I made from a piece of 1" re-bar. I forged it to shape with a very blunt square edge. I built up a bead of #6 Stellite on the edge and ground to shape and sharpness. He wanted it to clean off lumps of concrete left from knot holes in the forms. I fully expected it to come back in pretty bad shape but I was curious to see what would happen. Well, I found out! The edge was a little dulled

- not worth bothering to sharpen yet. No chips.


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Ted Edwards

I'd try some 1/4 x 1-1/4" W-1 or O-1 flat bar (from MSC or Enco?). Cut it to length, mill the bevel, drill and countersink the holes. You should be able to harden those with an O/A torch.

That should get you a blade that is RC 63 (O-1) to 66 (W-1) or so, a one, hour 500 degree temper should drop that to RC 58 or so. If you only have a home oven, an hour at 400 will get it down to RC 61-62 or so and that may work okay for a wood chipper.

You can get 9 blades our of a 36" piece of O-1 or W-1 which I would guess at around $60 or so. Your time does not count when you're working for yourself right? :>)

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Jack Erbes

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