Lapping Propellers to Shaft

2011 March 12
by Chris Brown

When shafts are in the machine shop for checking, straightening or repairing you should have the props and couplers lapped onto the shaft. Lapping the bore of the prop/coupler to the shaft taper ensures a 90-100% fit between the surfaces. If you are installing new propellers or there has been damage, this process becomes even more important. It is not uncommon to find a prop or coupler bore that is only touching in certain high points on the taper. A poor fit can cause the prop to be slightly off balance on the shaft. A poor fit with low contact is also more likely to become a loose prop at some point in time.

Lapping is the process of using a gritty paste between the two surfaces to allow them to grind together for a perfect fit. We prefer to lap while the shaft is in the lathe in order to take advantage of the shaft spinning and the overhead hoist to hold the heavy props and couplers. The process can also be done by hand while the shaft is still in the boat – but that is hard work and is less effective.

A video is worth a thousand words – here are two difference angles showing a lapping in progress.

Please give us a call when you are in need of running gear or shaft repair. Don’t waste money by having a machine shop only complete part of the job. Ask for everything to be lap fit.

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