How To: How to make a Woodruff key

This magdyno rebuild stopped for want of two keys – here’s how I got round it.


1: First find a piece of good steel bar (I used EN16T) of the right diameter for the slot – alternatively, turn it to size on the lathe. Then part it off as a disc, just slightly wider than the slot.

Step 1.jpg

2: You can then file it to a perfect fit in the slot – if possible it should be almost a press fit, because any slack creates movement which will wear the key and the slot.

Step 2.jpg

3: The next step is to carefully cut it in half with a hacksaw – Woodruff keys are generally less than half a circle, so the wastage due to the saw-cut won’t be a problem.

Step 3.jpg

4: Here’s the result – two keys made at once and you can get on with the next part of the assembly, rather than having to pack up and await the postman’s knock.

Step 4.jpg