A Primer on Multi Axis Turning

Multiple Axis Turning is a bit more complicated than single axis turning and can seem chaotic - totally upredictable - confusing as hell. But if you learn the fundamental concepts of multi axis turning - and you can - there is an order to it. And when you understand the fundamental concepts, you can apply them - and probably come up with some interesting multi axis pieces of your own.

Before we get to this multi axis primer I'd like to thank Barbara Dill for sharing her Structured Approach To Multi Axis Turning and kinda curse her for causing me to get semi-obsessed with really getting to understand the fundamental concepts of multi axis turning. You might want to visit Barbara's website ,download her papers on her Structured Approach and spend some time going through them - a couple of times.2

As you go through this Multi Axis Primer, you'll be seeing a lot of 2D and 3D illustrations of fundamental concepts, seeing terms of fundamental concepts and a bunch of words trying to define what they mean and how they relate. This PRIMER will come at the subject a bunch of different ways because different people "get new to them" ideas in different ways - and repetition - presented in different ways, often makes The Light Bulb go on. So as you go through this stuff, when you encounter something you think you already "got" - go through it anyway - it may help you "get it" even better - or not.

I think it's fair to say that most wood turners, whether we turn just Between Centers, or use Face Plates, Chucks, etc., turn on just ONE AXIS. And being limited to turning on just one axis, we can only turn ONE PROFILE per piece - whose CROSS SECTIONS are ROUND and that have only ONE Outside Surface. The profile can be as simple or as complicated as we care to make it., but the resulting piece will be ROUND - in horizontal cross sections. And it'll only have one outside surface.

But what if . . .
you could have TWO outside surfaces
- in one piece?

You can.
Here's a hint as to HOW..

Turning on Multiple Axes requires that you THINK DIFFERENT (to use an Apple ad campaign slogan).

You have to start thinking in terms of:

- more than one axis (DUH!)

- turning ARCS not just circles
- the COMMON AREA of two overlapping 2D PROFILES
- two or more OVERLAPPING 3D OBJECTS / FORMS (the 2D profiles "turned" into 3D things
- the COMMON VOLUME of overlapping 3D OBJECTS/FORMS
- INTERSECTING ARCS CROSS SECTIONS not just round cross sections
- more than just one OUTSIDE SURFACE for a piece
- VERTICAL EDGES not just horizontal edges
- TRANSITIONS at axes changes in direction

and more importantly

- that turned pieces DON'T HAVE TO BE "FUNCTIONAL" objects
They CAN BE just interesting objects - SCULPTURE.

Sculpture!? That sounds sort of Artsy Fartsy. I'm a wood turner, a craftsman, not an artist.

Well, if you're happy and content with turning round functional pieces - out of wood - more power to you. You can stop right here and go do something else creative.

But - if you are willling to consider or want to try something different using your lathe - read on.

Ready to start to THINK DIFFERENT?

Rather than think of a turning as only being done on a single axis and with one profile, start thinking of combining SOME of two or more single axis ideas into one piece.

Think MASH UP - a term for a genre of today's popular music - a little bit of this song, a little bit of that song, all mashed up together to make something that has sounds of the familiar, but put together, creates something that is different from any of the pieces that make up the Mash Up.

If you're older than thirty something and can't relate to Mash Up, think of Victor Borge, the very funny pianist , originally from Denmark. He mixes parts of Happy Birthday To You and Yankee Doodle Dandy - with a bit of Bach or Chopin or Beethoven, drifting fluidly back and forth between simple music and very complex music - to the delight of his audience. It's that place where you're hearing BOTH Happy Birthday To You and Chopin's Polonaise where we'll be playing.

Let's start off this multi axis primer thing with something familiar - two single axis bowl shaped forms, both with exactly the same profile, and overlapped as you'd effectively do if they were both turned in the same blank, each on its own axis.

First thing you notice about the OUTCOME is - that - IT AIN'T ROUND.

Instead of turning everything to round, this time we turn only PARTof each bowl in the blank. - ARCS NOT CIRCLES. We're only after what's in BOTH objects - their COMMON VOLUME. The horizontal cross sections of the COMMON VOLUME are LENS SHAPED in this example, not round. But the cross section of the COMMON VOLUME would be TRIANGULAR if we overlapped THREE bowl shapes - or- RECTANGULAR if we overlapped FOUR bowl shapes.

When you have cross sections that AREN'T ROUND you have FACES (plural!) - and - outside EDGES. Ain't no outside edges on ROUND pieces . . . unless you carve them in after the piece has been turned.

If you were to turn a simple bowl shape - THREE times in the same blank - each one on a different axis, you'd get something like this.

Note that the cross sections are triangular.
And the triangular cross sections don't have to be symetric,
the sides of the triangle can be different lengths,
as can be the profiles.


OK - with multi axis turning, we can turn a piece that IS NOT ROUND and thus can have MULTIPLE PROFILES and therefore something that looks different, depending on your vantage point.

Here's an example of two views of the same simple two axis, one profile multi axis piece

Notice how, in this next illustration, you can see the two EDGES in the two of the side views?

And here's an example of a simple three axis piece, without the color coding, again using only one profile.

Three EDGES, three faces
the faces don't have to be the same size


What we've been playing with has been somewhat familiar and relatively simple. But with multi axis turning, you can create pieces that are only vaguely familiar or not at all familiar - especially to a turner - who thinks One Axis, One Profile.

Here are five different views - of the same turned piece
turned on just two axes

Not seeing anything familiar?
Maybe if we add some more views.

Now are you seeing anything that looks kinda familiar?
Squint your eyes and look again.
(Hint: Look at the four objects on the right)

Maybe Police Line Up views will help.

The left and right side views of this virtual 3D piece looks sorta falconesque. The front and back views don't look anything like a falcon, though the front and back do have the same outline. THAT is one of the things multi axis turning brings to turning. Unlike a single axis piece, with its one axis symetry and only one outline / PROFILE, a multi axis piece can have VERY different outlines / Profiles -depending on your vantage point.

So let's use this one to start getting a feel for how this little more complicated multi axis stuff works and get some terms identified and defined.

Maybe a 3D view would be helpful. 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On the far left, AXIS 1, Axis 1's PROFILE in 2D, Axis 2 and Axis 2's PROFILE in 2D - with the two axes coincident (lined up with each other). The combined 2D AREA looks familiar though a bit fat. But remember - they'll be "mashed together" (overlapped),

Second from the left are Axis 1's 3D turned FORM and Axis 2's 3D turned FORM, neither one looking much like a Maltese Falcon - or each other. Again, remember that they'll be mashed together (overlapped).

Farther to the right, Axis 1's FORM overlapping Axis 2's FORM. Contained within the two overlapping FORMS is their COMMON VOLUME, the OUTCOME we're after. Around the COMMON VOLUME, which is the REAL WOOD or SOLID WOOD, is the AIR WOOD.

You've turned a square blank to round and know about INTERTUPTED CUTS where you're cutting edge is cutting wood, then out in air and back into cutting wood. Until you get to truning all REAL WOOD/ SOLID WOOD, your cuts will be interrupted. When turning a multi axis piece, at least half the time you'll be turning AIR WOOD - if you're turning on two axes. If you're turning on three axes, you'll be in AIR WOOD 2/3rds of the time. and only 1/3rd in REAL WOOD.

With multi axis turning you can turn ARCS
If you cut deep enough

It's the COMMON VOLUME which will be the end result, the OUTCOME, of your turning this mash up multi axis piece. Note that the two axes are PARALLEL to each other. They could also be slanted relative to each other (CROSSING AXES), such that they either INTERSECT or CROSS BUT DO NOT INTERSECT (more about those two axes orientation cases later)

The lower sets of illustrations show how you go from the 2D profile of each axis to the "turned" FORMS, the OVERLAPPED FORMS and the resulting COMMON VOLUME - the OUTCOME. The illustrations were alll done in Google's free SketchUp program. SketchUp is a very powerful tool to have in your bag of tricks if and hwen you get into multi axis turning. Google also has a free VIEWER that'll let you view virtual 3D models from any distance and from any vantage point. It's called SketchUp Viewer and you can downloaded a copy of the program to your PC or Mac.

(there'll be links to where you can download a copy later). SketchuP Viewer has almost no learning curve to climb since you use only a few of the tools that are in SketchUp. But it's a great way to get a feel for how to move around things should you decide to try SketchUp. There will be a link to a basic tutorial on how to use the tools of SketchUp to draw 2D profiles and how to virtually turn a profile into a virtual 3D "turned" form)

I should mention that the idea for this two axes, two profiles multi axis example was inspired by a piece by Peter Rand, one piece in a set of six multi axis pieces he entitled The Gathering. The left image had a bird of prey look - at least to me. When it comes to iconic birds of prey, the Maltese Falcon was what came to mind when I saw this piece, which doesn't at all look like a bird of prey in other views of Peter's piece.

Multi Axis turning isn't quite as simple and straightforward as single axis, single profile turning. There are a lot more variables and interactions of variables involved with multi axis turning. With multi axis turning anything you do NOW on the axis on which you're turning - will affect what you've already done previously - AND - may affect what you CAN or CANNOT DO NEXT. So this next illustration may give you an idea of what we'll be dealing with and how they affect the results - The Cause & Effect thing. The current buzzwords name for this thing is Mind Mapping - listing everything you can think of about a subject - and then making connections between them. It's just one of the ways of developing an understanding of something that may SEEM initially too complicated to understand. Other buzzwords version of the idea -The Scientific Method - The Org Chart or Organization Chart - The Flow Chart. All of them are there to help you build a mental model of something in order to understand it better and how it works. For now, just look it over. It'll make more sense later.

OK - so lets get to some of the TERMS & DEFINITIONS of multi axis turning, some of which have already been introduced - so we can use them to think about and communicate about multi axis turning - verbally or in writing - without having to include 2 1/2 D illustrations of actual 3D things , in order to share multi axis ideas. Don't worry if some of these terms don't make sense or that their definitions don't make sense - yet. Right now just go through them once or twice so when we get to using them and you see them in a virtual 3D model that illustrates them in a multi axis example, they'll be a little familiar.

AIR WOOD / REAL WOOD: When turning a square blank to round, until we've turned the blank to a cylinder, where we can make continuous cuts, we're making INTERRUPTED CUTS - the cutting edge contacting and cutting wood (REAL WOOD), then out in air, the cutting edge "cutting" through only the air (AIR WOOD).

When making continuous cuts we're turning FULL CIRCLES.
When we're making interrupted cuts, we can only turn PART OF A CIRCLE - an ARC.

ARC: Part of the circumference of a circle.

AXES - the number of axes for the FORMS used for a multi axis piece. Two axes are only the minimum number of axes - there can be as many axes as you chose to use. Where you place them, relative to each other will affect how the turned multi axis piece looks.

AXES CENTERS: Each axis must have two and only two centers - one on each end of your blank. You can't see the Axis running through your blank - but you CAN see its centers on the ends of your blank. Keeping track of which center on this end goes with which center on THAT end can get confusing when you've got two or more centers on each end of the blank - so we'll need to mark which one goes with which one. More about that later,

AXES TYPES: There are only two basic types of axes, but they have variations and the variations affect the OUTCOME

- PARALLEL relative to each other (You've already seen examples of PARALLEL AXES virtual 3D pieces)

- CROSSING: Axes are NOT PARALLEL, they slope or lean in opposite directions

INTERSECTING: If the two axes CROSS / lean in opposite directions - and intersect - anywhere - inside the blank or outside the blank - they're INTERSECTING AXES
NOT INTERSECTING: If the two axes cross / lean in opposite directions - and DO NOT INTERSECT - they're CROSSING BUT NOT INTERSECTING.1q

As you'll see later, CROSSING AXES affect the OUTCOME's CROSS SECTIONS. When they CROSS BUT DO NOT INTERSECT - the outside surfaces of the resulting piece will TWIST, the direction depending on which direction they cross. For this reason, Non Intersecting axes are also called TWISTED AXES. You can't actually twist an axis, but you can twist the OUTCOME if you have the axes cross each other - without them actually intersecting with each other. We'll be seeing how that works later. (I know, I keep saying - later. We WILL get to all these laters - later -honest.)

CHORD: Any line connecting two points on the circumference of a circle, whose length is less than the diameter of the circle.

CIRCULAR ARC: Part of the circumference of a circle. Since we're playing with a lathe, that's designed to turn circles, we'll drop the "circular" and just call part of the circumference of a circle an ARC

COMMON AREA: The AREA shared by two or more overlapping 2D closed shapes.

COMMON VOLUME: The VOLUME shared by two or more overlapping 3D objects - the 3D equivalent of Common Area.
With single axis turning, we turn a single profile. The profile can be any combination of just five types of cuts - the PRIMITIVES - a peeling cut to make a straight side, a convex cut (think bead cut), a concave cut (think cove cut), a V cut and a groove cut. That's all we have to play with - five basic cuts. But as a woodturner, you know how many nice ways you can use those cuts or combination of cuts to create beautiful turnings. The same PRIMATIVES can be used on each of two or more axes of a multi axis piece - to turn some interesting form / sculpture.

EDGES (VERTICAL): Unlike single axis, single profile, turned to round cross sections, turnings - multi axis turnings can have edges where parts of each axis' profile intersect. The line of intersection can be straight, though it DOESN'T HAVE TO BE A STRAIGHT VERTICAL LINE.

PROFILES ALIGNMENT: When turnng on more than one axis, each with its own profile, how the profiles align vertically, relative to each other, affects the look of the results / OUTCOME - or precludes getting ANY results / OUTCOME - at all.