Machining is often about mechanical precision and function, but not always. There is a huge body of knowledge concerned with machining for artistic effect. This article will sample some of the techniques involved.
Jeweling and Engine Turning
The beautiful patterns on the pieces in the image at the top of the page are made by engine turning, also referred to as jeweling. It’s seen in a number of different applications. Classic automobiles and hot rods used engine turning as ornamentation.
Here’s a motorcycle instrument pod done by reader Nate:
It’s often scene on the bolt and other parts of firearms as a decorative touch:
And of course, Charles Lindberg’s Spirit of St Louis airplane featured engine turning on the cowl:
How to do engine turning and jeweling of bolts and other parts
Engine Turning is very easy to do, at least in principle. You take an abrasive of some kind, put it on a rotating brush or buff, and drop it down onto the work in a pre-defined pattern. Typically, you overlap the plunges by half the diameter of your jeweling “cutter”:
Image via Tin Can Bandit’s Gunsmithing Blog…
Most jeweling is done by hand, often with a drill press, but a CNC machine can make short work of the task and CADCAM software can achieve a perfect layout. Try programming a plunge milling toolpath to achieve the desired effect.
What jeweling tool to use?
For your jeweling tool, there are a variety of possibilities. You can use a brush or buff with some abrasive compound. Many like to use Mag Wheel Polish as the abrasive. For the brush, a wire brush will last a long time.
This technique works, but is messy and a bit fussy. A method I like better is to chuck up an abrasive stick, such as a Cratex:
Cratex rubberized abrasive sticks…
Cratex sticks are just abrasive embedded in rubber. Use with a little WD-40 or other convenient lubricant and they work great. On a CNC, your machine’s normal coolant should be fine–no need to contaminate it by adding oil.
I use Cratex sticks quite a lot around the shop, so I bought their big assortment of sizes and grits. But, you can also buy single sticks very cheaply.
Engine Turning, also called Damascening, is a very straightforward process. It’s not hard, but it does require a lot of time and you need to be painstaking about how you overlap the pattern for best effect.
I prefer engine turning softer materials like aluminum. Obviously a rifle bolt will be quite a bit harder, so it will take longer.
Here’s a video showing some engine turning with a Craytex stick…
Experiment with the spacing pattern to create more interesting designs. Perhaps two sizes of circle would be neat?
Guilloche, Rose Engines, and Ornamental Turning
Fine jewellers scoff at the idea of engine turning being “jeweling.” It’s entirely too coarse a method for their needs.
Instead, they use a technique called “Guilloche” and a machine called a “Rose Engine” to do Ornamental Turning. BTW, it’s pronounced “Gee-o-shay” and is a French word. I will take this opportunity to apologize for not using the proper accent on the term Guilloché, but it is just easier to type without it and the use of the term without it appears to be commonplace on the Internet.
Their results are often spectacular:
The finally engraved patterns on the Faberge Egg are guilloche…
Watches are commonly adorned with guilloche patterns:
Guilloche patterns have also been used for years to decorate currency, stock certificates, and other valuable papers to make them harder to counterfeit:
How to Create Guilloche, Part 1: Traditional Rose Engines
Traditionally, Guilloche is created using a Rose Engine. Machinists will recognize it as an odd combination of lathe, 4th axis, and shaper. Complex and very Old School, but also very cool!
It turns out one of our G-Wizard Customers makes Rose Engines if you would like to look into purchasing one:
Mandala Rose Works Rose Engine…
I wrote a Customer Spotlight about Wade Wendorf’s great little company and products that you should check out.
There are some fantastic videos about this art as well.
Our first video is from a fine watchmaker that hails from right here in the good old U. S. of. A. Roland G. Murphy makes spectacular hand-crafted wrist watches, and their video is also extremely well done:
As you can see from the video, Guilloche is done with a machine that’s more like a very specialized shaper than a lathe or milling machine. This results in the markings on the material having a much different character and a lot more texture.
In addition, these old machines are entirely hand powered. They use cams (called “Rosettes”) to give the workpiece a periodic “wobble” that results in the distinctive curves and curlicues that are characteristic of Guilloche. If you watch closely, you can see that the operator has to manually start, stop, and position the cutter to keep the design within the outline it is bounded by.
Here is another great video from the great old watch maker Vacheron Constantin:
It’s a little less technical but no less fascinating to watch this fine art form being done by VC’s “Master Guillocheur”. There are some great closeups showing the shaper-like tool peeling chips off of watch faces.
Here’s a last one, in the spirit of fine watchmaking of the other two:
I believe this video is from Victorinox, and there are some fascinating insights to be found in it. The discussion of how the Guillocheur uses his sense of touch and visual indication of chip size and formation to create the best effect is wonderful.
Also note that this Rose Engine has not only the normal Rosette cams, but an additional cam at right angles that he uses to create more geometric patterns. Heretofore I had associated Guilloche primarily with curves, but we can see this is not a requirement.
Looking at these wonderful old machines, my first inclination is to dive into creating a software simulation of a Rose Engine that could be used to create g-code for a CNC. Simulating the motions of the machine and allowing the creation of the Rosettes from perhaps DXF files would be straightforward if complex and voluminous. It would be a fascinating project for me, but one that will have to wait a while as there are more pressing commercial realities for CNCCookbook!
How to Guilloche, Part 2: Using CNC
It’s possible to do engraving on a CNC that follows a Guilloche pattern. The result won’t be exactly like a Rose Engine because you’re not performing shaper like cutting, but rather using a rotating engraving bit or spring loaded drag engraver.
Perhaps some enterprising CNC’er will construct a shaper style engraver that actually incorporates a 4th axis motor to control which way the cutter faces. Then you really could achieve the full results. Meanwhile, I digress.
Also, much as I would love to write a Guilloche program of my own, there are already some very nice ones out in the world.
Guilloche patterns can be generated mathematically, for example by this program.
That’s quite a nifty little free program to get started with.
I also have a copy of what is probably the world’s foremost and sophisticated Guilloche software:
It’s called Excentro and it is quite sophsiticated. Apparently it has been used to design modern guilloche patterns for modern banknotes of several countries, so it is likely the ultimate.
There are other packages out there, so you’ll want to pick one that you’ll use to create your patterns.
Their output is a vector graphics file, so your next step will be converting that to a DXF file so your CAM software can access it. Adobe Illustrator, Inkscape, and other vector drawing programs can do this.
Once you have a DXF, you are ready to import it into your CAM software and generate an engraving toolpath from the pattern.
For a cutter, you can use a V-Bit, ballnose, or even a drag engraver, depending on the effect you want to achieve.
When you get ready to apply a pattern like Guilloche using CNC, you’ll have to decide what sort of cutter to use. It’s easy enough to use a V-Bit or even a small ballnose endmill, but another approach is called “Drag Engraving”.
Tormach has a nice article on their blog about drag engravers. This is a handy way to get started. One thing about spring-loaded engravers that helps is they will track a surface that isn’t perfectly flat. The Dapra unit looks like it has some tolerance for that too. Seems like no big thing–after all, you could just facemill it before engraving, no? Well, what if you want to engrave on a cylinder using a 4th axis or any other curved surface? If that happens, a drag engraver is one way to go:
Caleb Kraft demonstrates drag engraving on the Tormach 440…
A drag engraver is a pretty good way to get started with engraving, though you can also do very well with a small ballnose endmill. The drag engraver is quite a bit more durable though!
There are other artistic machining pursuits, such as engraving, but these two seem to go together. One is quite simple (engine turning) and the other can be as unbelievably complex as you choose to make it (guilloche). Both are fascinating!
Have you tried either? Tell us about your artistic machining in the comments below!
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Bob is responsible for the development and implementation of the popular G-Wizard CNC Software. Bob is also the founder of CNCCookbook, the largest CNC-related blog on the Internet.