Post by rod on Jul 4, 2021 17:35:36 GMT -6
This problem may not be the case for North American or European users but it sure is for us in OZ.
MacDon knife guards always wear out the wear bar on the back of the guard …. well before the edge on the finger(s) ….. & I think the main factor attributed to this is, speed of harvest.
We all know that a knife with single finger guards has a maximum cutting speed of about 12k’s before the stubble start looking ragged. The ragged - shark tooth - look comes from the crop being pushed forward as it’s being cut.
At 12ks, that 3.3mt per second forward movement. MacDon knife drive pulley specs say running speed should be between 600-640rpm. Someone can work out how many knife oscillations per metre of forward travel that is ….. even better if it in a graphic. I’ve heard some people have adjusted the knife speed to 800rpm plus ….. & I’ve also heard that speed increase has led to cracking issues elsewhere. I’ve heard this ….. I haven’t seen this for a fact.
Now at 12k’s & over, the pressure of the crop is pushing the knife (sickle) backwards & hard against the wear strip of the guards ….. because it can’t cut it quick enough …… hence you end up with a ragged stubble look because the stubble has been torn off & not cut off. And this (theory) has more credence - for when you need to replace the knife, the complete knife has a horizontal bow in it - suggesting the (crop) pressure is pushing backwards hard on the knife.
Now the reasons for the speed theory.
I have another MacDon 7.6mt 9 bat reel that’s for rice. Harvest speed is often no more than 4.5k’s. Rarely over 6k’s & sometimes less than 2k’s. In 6 years, I haven’t changed the genuine MacDon knife guards! I’ve changed knife sections every year …… but not the guards. There’s some wear on the cutting edge ….. but none on the wear bar at the back of the guards. The reason (theory) is the lack of forward speed on this head in rice is not pushing the knife back hard against the wear bar.
Now getting back to cutting at or over 12k’s on the 12 or 13.7mt MacDon in cereals.
I know from experience that double cut (double the fingers) guards make a massive difference to cutting speed, knife drive load, longevity of guards & knife sections & clean cut of stubble ….. no ragged/torn look.
There’s also the issue (visual & not technically verified) that with double cut guards, the crop material is definitely cut quicker & when cut it (crop material) always falls backwards, cleanly & evenly onto the mats, presenting a better more even feed to the entire machine. I’ve observed this fact many times over & it makes a difference to overall machine performance. I can understand those that have never experienced double cut guards & high harvesting speeds would say “this is bullshit ….. because the mats will sort it out”. Each to their own …. but I’m saying what I’ve seen & experienced.
So, what do people think of this whole theory?
MacDon knife guards always wear out the wear bar on the back of the guard …. well before the edge on the finger(s) ….. & I think the main factor attributed to this is, speed of harvest.
We all know that a knife with single finger guards has a maximum cutting speed of about 12k’s before the stubble start looking ragged. The ragged - shark tooth - look comes from the crop being pushed forward as it’s being cut.
At 12ks, that 3.3mt per second forward movement. MacDon knife drive pulley specs say running speed should be between 600-640rpm. Someone can work out how many knife oscillations per metre of forward travel that is ….. even better if it in a graphic. I’ve heard some people have adjusted the knife speed to 800rpm plus ….. & I’ve also heard that speed increase has led to cracking issues elsewhere. I’ve heard this ….. I haven’t seen this for a fact.
Now at 12k’s & over, the pressure of the crop is pushing the knife (sickle) backwards & hard against the wear strip of the guards ….. because it can’t cut it quick enough …… hence you end up with a ragged stubble look because the stubble has been torn off & not cut off. And this (theory) has more credence - for when you need to replace the knife, the complete knife has a horizontal bow in it - suggesting the (crop) pressure is pushing backwards hard on the knife.
Now the reasons for the speed theory.
I have another MacDon 7.6mt 9 bat reel that’s for rice. Harvest speed is often no more than 4.5k’s. Rarely over 6k’s & sometimes less than 2k’s. In 6 years, I haven’t changed the genuine MacDon knife guards! I’ve changed knife sections every year …… but not the guards. There’s some wear on the cutting edge ….. but none on the wear bar at the back of the guards. The reason (theory) is the lack of forward speed on this head in rice is not pushing the knife back hard against the wear bar.
Now getting back to cutting at or over 12k’s on the 12 or 13.7mt MacDon in cereals.
I know from experience that double cut (double the fingers) guards make a massive difference to cutting speed, knife drive load, longevity of guards & knife sections & clean cut of stubble ….. no ragged/torn look.
There’s also the issue (visual & not technically verified) that with double cut guards, the crop material is definitely cut quicker & when cut it (crop material) always falls backwards, cleanly & evenly onto the mats, presenting a better more even feed to the entire machine. I’ve observed this fact many times over & it makes a difference to overall machine performance. I can understand those that have never experienced double cut guards & high harvesting speeds would say “this is bullshit ….. because the mats will sort it out”. Each to their own …. but I’m saying what I’ve seen & experienced.
So, what do people think of this whole theory?
