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Guilloche


#1
   Thanks all who answered my guilloche question, especially Ed
Colbeth for directing me to Peter Rowe's utterly fascinating
article. 

Blush … Glad you enjoyed it.

   Peter, if you're out there, I have one last question: can the
traditional Faberge engraved effect be achieved with a modern CNC
machine (for example, Servo Products with Precise high speed
spindles) as with an old Plante, Hall, or Field engine turning
machine?  Or is there a distinct quality to hand work? 

I suppose it can, if you can get the tooling in a rotary tool machine
(a mill) to produce a cut similar to an engraved cut from a fixed
pointed tool. this will be difficult, if you think about it. But
where there’s a will, there’s a way, especially if you start thinking
about diamond tooling, I’d guess. The thing about the classic engine
turning machines is that the tool, which looks much like a standard
lathe tool, is an angular point, leaving a cut with distinct flat
sides to each side of a sharp bottom edge. It’s hard to get a rotary
cutter to leave quite that same character of cut. But not
impossible.

There will be some other limits, too. One is that an engine turning
machine uses a depth stop affixed to the cutter itself, so that, under
hand pressure pushing it into the work, it can only dig to a certain
depth. That allows it to cut a uniform depth cut even if the work
surface itself is not flat and paralel with the direction of travel.
You can easily engine turn shallowly formed surfaces, for example.
The cutter simply tracks along the work, with the depth stop limiting
the cut depth. Simple and direct, but not as easy to do with a
standard machine tool, unless you’ve also formed the surface being
engine turned, so the computer knows exactly where that surface is.

As to cutters, It might be worth trying not a rotary cutter, but a
diamond drag engraving point such as is often used in jewelry
engraving pantographs. Again, not quite the same cut, but it might be
a visually acceptable substitute. In fact, it’s possible, with
considerable work, to produce a sort of engine turned pattern with a
standard pantograph jewelry engraving machine. You need to make a
long pattern of the wave shaped cut, and then devise a means of
"indexing" to move that pattern, or the work, between successive cuts.
Before I bought my straight line engine, I did a little bit of this
by using a woodworkers jig (I forget the name, but they’re easily
found) which set measurements using a little toothed rack that would
set discrete index like steped measurments. That allowed me to move
the pattern a precise interval between cuts. it was a limited setup,
but let me do a little bit of this sort of cutting. I used both a
diamond drag engraving point, and a home made non rotating cutter
held in the rotating cutter’s holder, to use the depth stop setup the
New hermes machine uses with rotating cutters.

As to the “hand quality” of the cut, this is less an issue than you
think. While the cutter is pressed into the work by hand pressure, for
the most part, this is a machine tool. The cutter is held by the
machine, and indexed laterally for cut spacing by the machine, and the
line and shape of the cut is completely controlled by the machine.
The only things that differentiate this as a hand operated machine is
that if you’re in a hurry, you can make mistakes with settings, and
get cuts “wrong”. Or you can cut so fast that the machine fails to
track the pattern bar, again screwing up a cut. Now, if the cutter
you’re using is a standard steel cutter, sharpened with normal
grinding wheels, etc, then like a poorly polished or unpolished
graver, the cut will have striations, yet still be smooth and bright.
This is difficult or impossible to duplicate exactly with a rotating
cutter in a mill, so if you’re examining the cut closely enough, using
a different type of machine will show up. But this is a minimal
aspect of the whole effect, and some engine turners use modern style
diamond tipped tooling, which gives virtually perfectly polished
bright cuts. Looks great. Certainly does not look “hand cut”. I
think that most of the really notable effect of the engine turned
effect is simply the “moire” patterns formed by the multiple
overlapped or almost overlapped cuts. THAT effect will exist with
almost any type of cutting tool. To illustrate, one commen use I make
of this effect is roll printing my silver or gold against an engine
turned piece of steel. The result is an engine turned pattern of
RAISED lines, not incised ones. Totally different, yet remarkably
similar in overall visual effect once the jewelry is done.

The quality of the cut and the work will obviously reflect the way
the work was done, and the equipment used to do it. While I suspect
you’ll never quite duplicate, exactly, guilloche/engine turned effects
with a CNC mill, you might well produce a finish with equal decorative
value. And there are, no doubt, a whole slew of patterns you can
devise and create with your computer, and cut on a mill, which can not
be cut with an engine turning machine. Try it, is the best I can
suggest, and see what you can come up with. If it differs from an
engine turned effect enough to be obviously different, well, so be
it. That does not mean that it has to be an automatically inferior
look. And the CNC has the obvious, major advantage of being capable
of cutting intricate, complex patterns on your work full time, seven
days a week if you want, while your hands are still free to do other
stuff. Engine turning machines are very efficient and versatile at
producing the specific patterns they’ve been designed to produce. But
you still have to hand crank that machine through each and every cut.
Believe me when I tell you that this can get rather tedious and time
consuming sometimes…

By the way, as to printed reference materials on engine
turning/guilloche work, the best reference (english language) that I
know of is Martin Matthews limited edition (and now out of print)
book, “Engine Turning 1680-1980 The Tools and Techniques”. ISBN
0-9508801-0-8 difficult to find, and probably costly. (My copy cost
me over a hundred dollars in 1988) But if you can find a copy, it’s
well worth the cost if you’ve an interest in the subject. Another
easily found reference on the general subject are the various Dover
reprints of the series of 5 1843-1884 books on "Turning and Mechanical
Manipulation) by Charles and John Holtzapffel. volume five,
especially, is germain to engine turning… And, if you happen to
read German, and can find a copy, there’s “Handbuch der Gravierkunst,
Ein Werkstattbuch fur die praxis und den fachschulenterricht, von Curt
Steubel” Fachbuchverlag, Leipzig, 1957. The info I’ve got on this
is limited. My copy is just a zerox copy of about a dozen pages,
obviously part of a much larger text. I don’t know if the
aformentioned title is the books whole title, or just a chapter within
a more general title. I think this is the chapter on engine turning
in a larger book with the aformentioned title. But I’m guessing. I
spoke some swiss-german as a child, but not any longer.

Peter Rowe