DIY Magnetic Prop Balancer

 

Metal props are very effective but need to be balanced to reduce vibration and provide the most efficient drive for your boat.

Here is an easy to build prop balancer that you can make using bits that most of us have lying around our workshops.

Parts you will need:

An old brushed electric motor

An old propshaft or steel screw (at least 30mm long) that will fit the internal bore of your prop.
Note: A 3/16th piece of K&N tubing slipped over an M4 machine screw will be a snug fit for a 3/16th bore prop.

A vice

Method

2. a. Cut the propshaft or screw down to 2-3 inches (50-75mm) long. A piece of 3/16th K&N tubing will fit snugly over an M4 screw
    b. Wrap some tape around the thread to prevent it being damaged and put the shaft into the chuck of a drill. File each end down to a point
        whilst rotating the shaft in the drill. A more professional approach would be to use a lathe for this job (but most of us do not have access
        to such a tool).

3. a.Open your vice and place the magnets against the jaws.
    b Adjust the distance between the jaws so that the gap between the magnets is 1mm wider than the length of the prop prop shaft.

4. Put the prop onto the shaft and place one end of the shaft against one of the magnets the other end will be floating close to the other
    magnet.

5. You are now ready to start balancing.

1.    Dismantle the motor and remove the two "C" shaped magnets

Basic Guide to Prop Balancing

I do not claim to be an expert at prop balancing but here are the basic rules:

1. Use varying grades of wet & dry paper to remove material from the propeller, finishing with 1200 grit paper. 
2. Only remove material from the back of the prop (the side facing the front of the boat).
3. Sharpen the leading edges using a flat needle file file and finish with wet & dry.
4. Spin the prop gently on the balancer. The heaviest blade will always settle downwards.
5. Mark the lightest blade with a dot from a felt pen and remove material from the other blade.
6. Keep checking the balance as you go.
7. Eventually you will reach the point where neither blade will consistently sink to the bottom. Your prop is now balanced.
8. A surface drive propeller will have a small flat section on the trailing edge. Run a file along this edge to preserve the wedge shape which allows
    water to break away cleanly then check the balance again. 

 

Health Warning

Most top class racing props are made from Beryllium Copper and the dust produced during balancing is toxic. To protect yourself, it is recommended that you remove material from the prop under running water and wash your hands thoroughly afterwards.