Static balancing a blade is the last step in the restoration of the blade assembly and is a crucial step in the restoration process. Imagine spending countless hours on perfecting the paint, polishing, and electrical only to turn the fan on and have it wobble off the table! I will provide a detailed, step by step explanation of the static balancing procedure.
Remember, static balancing is not the only step in making a perfectly balanced blade. Dynamic balancing also needs to be accomplished in order for the blade to be considered “fully” balanced. We will discuss dynamic balancing in another post. Typically when static balancing is performed the blade will have already been fully polished and lacquered. However for the sake of this article I am only using this “unrestored” blade assembly for demonstration purposes.
Tools Required:
- Dubro Prop Balancer or equivalent (These are used to balance R/C airplane propellers)
- Correct size shaft to fit inside the blade hub (Common sizes include: 3/16”, ¼”, 5/16”, 3/8”, ½”, or 1”) Shaft length should be between 6” and 12”
- File or narrow belt sander
Side view showing how to install the balancing shaft within the Dubro stand.
Step 1: Determining the “Heavy” Blade
With your newly polished and lacquered blade, you want to be careful while static balancing; you don’t want to accidentally scratch a wing!! Cotton gloves are highly recommended for this procedure (except when installing the oily shaft). Select the correct size shaft and insert it into the hub assembly. Assemble the Dubro balancer as shown in the pictures and mount it to something so it doesn’t tip over. If you assemble it as pictured, you will not need a counterweight on the opposite side of the shaft. Clean the Dubro disks with mineral spirits for storage and re-oil it using any low weight non-detergent oil before next use. Next, you want to create a system for labeling the wings. Place a small piece of masking tape and mark it 1 through 4 for four wings. Now, slightly spin the blade in its normal rotation (clockwise while looking at it). You will find that the blade will take forever to stop if spun hard. Let it settle and note which blade rests on the bottom (see pic). Now is the time to remove material!
The heavy blade will always fall to the bottom. Material can then be removed from this blade only.
Step 2: Lightening Up That Heavy Wing
Now that you have determined the heavy wing, it is time to start filing or applying light pressure to a fine grit belt sander. Only file or sand on the TRAILING edge of the wing to prevent deformities to the leading edge. You can easily determine the trailing edge by remembering the correct rotation of the blade, clockwise if you recall. Remove small amounts of material at a time! You want to be able to put the blade back on the Dubro and have it still drop to the same heavy wing. However, as you file or sand, the wing will move slower and slower to that lower position, indicating that you’re almost there! Have patience and continue filing or sanding until there is no more “heavy” wings. You will know that you're done when you spin the blade and it stops at a different location every time. If balancing is performed right then your fan will turn on and spin vibration free.
The blade is done when the heavy wing will no longer fall to the bottom consistently.
Step 3: Storing Your Static Blade Balancing Equipment
Clean the Dubro balancer’s disks with a few drops of mineral spirits to clean off the old oil. This will ensure that when you’re ready to use it again, there will be no hardened, possibly stick oil (especially if you don’t use it very often). Then, cover it with a plastic bag to preserve it. Next, clean off the shaft with any solvent (mineral spirits, lacquer thinner, etc.), re-oil it, and place it in a zip-lock bag for future use. It is really important to prevent rust or any imperfections on the shaft, ensuring it will always be reliable.