You have probably seen engine turned parts and never knew what the finish was called. Engine turning, sometimes called jeweling, is common on everything from watches to firearm bolts and barrels. One of the most famous uses of engine turning was on the Spirit of St. Louis shown below. Jigs and templates can be used to aid in the process, but jewelry is still a very labor intensive process. The pattern is created by machining overlapping circles into the surface. The pattern is determined by the size of the bit and how much overlap is used.
Craytex or wire bits are commonly used. For aluminum I prefer a wooden dowel and cutting compound. What alloy you are trying to jewelry determined what cutting compound you should use. For aluminum, regular heavy compound works well. For tougher metals like steel I use a mixture of cement, cerium oxide and water. On ever softer metals or for a finer pattern, I use a leather pool cue tip glued onto a dowel for a finer finish. No matter what material you are working with keep your drill speed around 1100RPM.
A mill with an automatic feed can make short work of mass produced parts. For smaller one off items, the setup time can not be justified. A drill press and a little patience will achieve great results. If your drill has a laser guide system you do not need to mark up your part. If you do not have a laser guide system, you will want to draw out a grid on your part to give you a pattern to confirm to. A typical pattern overlaps the circles by 25%. So if working with a 1 "dowel, you would want to mark a spot to jewel ever 1/4".
The key to great results is consistency and preparation. You must apply cutting paste at a regular interval. You must also apply the same force each time for the same duration if you want uniform results. I used a three second duration with five pounds of force for this guide. The duration or force applied will vary depending on your materials, and desired results.
Start in one corner and work down all the way before starting another line. As you progress, clean and reapply compound to the bit at regular intervals. If the dowel or wire brush begins to mushroom you need to change brushes or cut the dowel to a fresh tip. You can fight mushrooming on wire brushes by wrapping the tips in some tape.
Whenever you reach a stopping point, remove your piece and clean and it off. Inspect your work to make sure you are getting clean clear circles and make any needed adjustments.
When you have finished the entire piece, wipe it with a degreaser and inspect for any spots that may need touched up. Remember, jewelry is an art form and requires patience. A 2 "x2" part has 100 circles assuming you are using a 1/4 "bit.
For more information on engine turning or other finishing tips check out volvospeed.com