Thanks Leon.
While I see your point, I do wonder. My thinking was that if balanced in opposing directions, the effect would be minimal if any. Is there a significant difference of equal pull in 2 vs 4 directions? Not being an engineer, I wouldn't know how to computer. Maybe Jack from China can get an answer?
So after reading your answer above, I decided to investigate further.
Weight of blades:
1 - Hammer = 26.6 oz
2 - Y w/ spacers = 22.2 oz
2 - Y only = 19.9 oz
That's 4.4oz difference per station, hammer vs Yw/spacers. (4 rows of 7 stations per row)
So if I had a heavier, 6.7 oz spacer they would be equal. I'm thinking I could probably get that weight making a spacer from my old, broken hammers with some trial and error.
Thoughts anyone?
BTW, wife has confirmed she likes the hammer cut better, more uniform.
Scale pics of blades:
View attachment 384185
View attachment 384186
View attachment 384187
David Sent from my iPad Air using TractorByNet
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David-
you have to think of it in this manner;
1.Your clock has 12 hour points
2. Your flail mower has four rows of knive stations.
3. location one is located at 12 o'clock
4. location two is located at 3 o'clock
5. location three is located at 6 o'clock
6. location four is located at 9 o'clock
NOW
row one has 18 pounds of hammer knives mounted
row two has 6 points of side slicers
row three has 18 pounds of hammer knives
row four has 6 pounds of side slicers
YES I know I am getting there-bear with me
NOW we are are the point where we will bring out the buckets.
you have 4 new galvanised 12 quart buckets, you put 14 pounds of sand in two buckets.
you then put 28 pounds of sand in the other buckets.
you can safely spin the first set of buckets without losing sand as long as you spin fast enough.
you can safely spin both of the bockets with 28 pounds of sand as long as you spin fast enough to avoid spillage.
you take all four buckets and hang them on the four post/strut clothesline with equal lengths of clothesline in the back yard/lanai in your case?
Now I have you tieing the buckets with 4 foot pieces fo clothes line on to each strut with good knots-wife should be on he mainland when this is going BTW.
grab the car out of the garage and the put the rear end on Jack stands placed on on 2 by 12's and take one of the rear wheels off.
grab an old rim and put it on the axle without the tire.
get some good rope and loop it around the wheel, crosss the rope and wrap it
around the pole for the four strut clothes line until its tight.
tie a good knot connecting both ends.
Start the car and put the car in drive.
Gradually begin speeding up get your radar gun out and occasionaly stick it out the window pointing at the rear end of the car.
As you are speeding up, or as it is referred to as "spooling up" in aircraft circles the stress on the 28 pound buckets is concentrated on the base of the galvanised buckets because the THROW Weight is greater and will be rocketed off somewhere in the neighborhood and hopefully not through the plate glass doors of you home which is why you want the wife on the mainland.
IT all has to do with throw weight of each row of kives creating more stress on the flail mower rotor bearings
in total as the entire circumference of the bearing is recieiving an alternating overload
at three oclock and nine oclock AND ALL the ball bearing roller and bearing races are recieving
this overload intermittantly while the flail mower rotor is spinning attempting to reach 2,200 RPM +-.
Tim The Tool Man Taylor and Rube Goldberg would be proud
AS Bart Simpson would say; I didn't do it, nobody saw me do it, nobody can prove I did it!
About your side slicers they dont look very sharp and that is a problem, the edges should not be blunt.
If you have a wet well kitchen knive grinder you need to put an edge on them
. 
