Balancing mower blades w/o round center hole

[Giff Kucsma 2]

I just replaced the spindle bearings in my RM-367 mower deck.  I have a new set of OEM mower blades, but I'm wondering if anyone has found a good way to balance these blades that do not have a round center hole in them.

 

 

[Ed Kennell 38,112]

 to the   Giff.         Clamp a knife edge in a vise and lay the blade center on the edge.      Be careful....don't get cut.

[WHX?? 48,813]

 Giff, Ed' suggestion works well.

Another piece of advice.... DO NOT THROW THAT BLADE BOX OUT! That is  cool! 

[gwest_ca-(File Mod) 11,039]

Was never happy with the balance using the "hang the blade on a nail" method. Tried all the available balancers except the $200+ models for obvious reasons.

 

Came up with an economical solution and didn't realize until finished why it is an improvement. If you have a 2" wide blade with a 3/4" hole hanging on a nail approximately 31% of the blade weight is above the nail and 69% of the blade weight is below the nail. That 69% below the nail pivot point masks a good portion of the out of balance condition.

Pilot bearings used on woodworking router bits come in sizes matching the blade center holes of most blades and use a very light lubrication making them ideal for a balancer. Just mount the bearing on a horizontal machine screw fixed to the wall and hang the blade on the bearing. Grind until the blade stays where you put it. One thing I learned is it should be done indoors because an unnoticed slight breeze will windmill the blade it pivots that easy.

The solution is to get the center of the blade on the pivot point.

 

The 5/8" x 3/4" double-D center hole stumped me for a while. Ended up making a bushing from 3/4" round aluminum solid bar with a 3/8" hole drilled in the center. Filed 2 equal flats until it fit snugly in the hole and hung it on a 3/8" OD bearing. Problem solved.

 

Some observations.

When previously sharpened and balanced blades come off the deck dull and loaded with gunge they are still balanced if they have not hit something.

 

Have never come across a new blade that was not balanced as they should be but always wondered. Have a new 3" x 30" 9 lb. brush blade used on the Gravely 30" mowers and it came balanced.

 

Unbalanced blades are what cause decks to crack around the spindle housings. Many years ago I drilled the ends of cracks around all three spindles of a gentleman's deck and then bronzed the cracks where the metal was not missing. Should have been scrapped or at least welded with steel. He brings me the deck for sharpening and balance twice a year and as of two weeks ago the bronze has not cracked. Amazing.

 

Made a balance stand with a 3/8" x 7" x 7" plate base. Three adjustable legs for leveling. In the center is a 3/4" square tube/post about 10" long that has the different sized bearings attached to the top sides of it. My thought was the bearings need to be perfectly vertical for accuracy but that is not necessary. As long as the bearing is reasonably vertical it works. The three legs make the stand very stable.

 

Garry

[Jerry77 1,218]

1 hour ago, gwest_ca said:

I drilled the ends of cracks

Good job ! it is the only way to stop a crack from spreading....

[Giff Kucsma 2]

On 4/25/2017 at 6:02 PM, Ed Kennell said:

 to the   Giff.         Clamp a knife edge in a vise and lay the blade center on the edge.      Be careful....don't get cut.

 

Thanks, Ed.  I don't know why I tend to over-think problems like this.  I didn't have a knife handy but did have an old wide blade chisel that worked as well.

 

[WVHillbilly520H 10,373]

My dad has had/used one of these aluminum balancers for as long as I can remember and I have used the plastic version with success but have finally got myself an aluminum one, 18 years on my 520 deck and no stress cracks or dad's CC ORIGINAL he's owned since '76-'77, well worth the $7, Jeff.