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 jeweling is still a very labor intensive process.
The pattern is created by machining overlapping circles into
the
surface of an object. 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 jewel determined what
cutting paste 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 1000RPM.
A mill
with an
automatic feed can make short work of mass produced parts.
For
smaller one off items though, the setup time cannot 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. 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 combat
mushrooming on wire brushes by wrapping the tips in 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.
When you
have finished
the entire piece, wipe it with a degreaser and inspect for any spots
that may need touched up. Remember, jeweling is an art form
and
requires patience. A 2"x2" part has 100 circles assuming you
are
using a 1/4" bit.
