Making small carbon propellors

Martin Newell

August 2004

Information on the basic technique for making carbon fiber propellors is available elsewhere. It is a very effective technique and enables a wide variety of strong and light propellors to be made. I have my own variations on the technique that you may find useful.

In the published technique the propellor is made by laying carbon cloth and epoxy over an existing propellor and compressing it with shrink tubing. After curing and trimming you locate the center, drill a hole and mount a hub in it.

The main change I make is in locating the hole for the hub and in making the hub. Before laying the carbon cloth over the existing propellor, insert a small pin the size of the propshaft into the front of the propellor, protruding about 1/16". When laying the carbon cloth over the propellor, gently work the cloth over the pin. When shrinking the shrink tube over the propellor, gently rub a file over the top of the pin to make a hole in the shrink tube so that it can shrink down around the pin.

After curing and removing the propellor from the mold, you now have a perfectly aligned, centered hole in the prop. This can then be reamed or drilled out to accommodate the hub.

For propellors for use with geared pager motors with 1mm prop shafts, the hub can be made from pieces of 3/32" shrink tubing. Place a short length of shrink tubing on a piece of wire the same diameter as, or slightly smaller than, the diameter of the prop shaft, and shrink it on using a small flame. Drill or ream out the hole in the propellor to be a push fit for the shrunk tube, still on the wire.

Glue the prop to the shrink tube with a very small amount of glue - don't build up a fillet of glue between the prop and the shrink tube. Put the wire into an electic drill or some other means of rotating it fairly slowly. Position yourself so that your eye is in the plane of rotation of the prop. Start the prop rotating. Watch for, and correct for, two kinds of alignment.

The first is to ensure that the tips of the prop pass over the same point in the background behind the prop. You may want to put a marker on the bench against which you can check this alignment. Adjust the prop on the shrink tube to correct for any differences.

The second alignment is to ensure that the angle of attack of the two blades are the same. I do this by focusing on the whole profile of each blade as it rotates. Both blades should appear to be the same width as they rotate into view, so that it appears as if the same blade is repeatedly appearing. Twist the prop along its length to correct for any differences.

Finally check that both types of alignment are true, and leave it for the glue to harden. Epoxy can be better than CA for this, to give you time to carry out the alignment procedure. Alternatively you can rely on the push fit of the hub and align with no glue, then carefully apply a very small drop of glue to lock it in place.

When the glue has hardened take two short lengths of 3/32" shrink tubing and push them over the existing hub, both in front of and behind the prop. Using a soldering iron, shrink these pieces down. Now apply a fillet of glue around the outer shrink tubing pieces where they meet the prop. This makes a strong hub with the prop sandwiched between the two outer pieces of shrink tubing.