Nested Helix

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Introduction: Nested Helix

In this Instructable I’ll explain how to make nested helices (spirals) from wooden dowels or sticks. A few years ago I came across this article in Make Magazine that describes a spiral cutting technique first published by Steve Garrison. I was very intrigued, but other projects kept me busy. Finally, I decided to design and build my own jig to cut these spirals.

Step 1: Basic Concept

The basic idea is to use a scroll saw to cut a dowel lengthwise. If you turn the dowel while cutting it, you will end up with a spiral cut. Some people might be good enough to do this by hand, but I am too klutzy to do that. You have to be very steady and accurate, otherwise the two parts will not separate (unscrew) after the cut, or they’ll break apart while cutting. Also, if you want to do several consecutive cuts on the same dowel you need to be very precise.

I decided to build an Arduino controlled jig that uses two stepper motors: one to advance the dowel into the blade, and a second one to turn the dowel around it’s long axis. By adjusting the speeds of the two motors independently, you can make a spiral screw of any pitch. I define pitch as inches advanced per revolution. A 1/4-20 standard machine screw takes 20 turns to advance one inch; so per my definition it has a pitch of 1/20 inch per revolution. You will need a spiral blade for the scroll saw; i.e. a blade that cuts in every direction. This is very important! I use Olson #0 spiral blades. Since this is a very fine (46 TPI, 0.032 kerf) blade; and since I am cutting very, very slowly (20 to 30 minutes for one 10” long spiral cut), the resulting cut is very smooth and requires no sanding.

This technique WILL NOT WORK ON A BANDSAW as there are no spiral blades available for the bandsaw. Repeat: it will not work on a bandsaw! You might be able to set up a jig with a Dremel motor or router and a small cutting bit; but your kerf will be much larger.

Step 2: Jig

I will not go into great detail about the jig; that may be a future Instructable if there is sufficient interest. The pictures and movies should be helpful. A brief description of the jig is as follows.

The central part is a 26” long sled that is driven towards the scroll saw blade by a stepper motor and a 1/4-20 threaded rod. As the stepper motor turns the threaded rod, the sled is pulled forward. Inside the sled, the dowel is mounted similar to a lathe. A second stepper motor turns the dowel around its center axis at a speed controlled by the Arduino program. The sled is mounted into a 30" long outer frame that clamps securely to the scroll saw table. When the system runs, the inner sled advances the dowel into the scroll saw blade while the dowel is being turned. Choosing the advance speed and the turning speed gives you a great deal of flexibility over the shape of the spiral.

The stepper motors are controlled by an Arduino micro-controller. Programming is done in the Arduino IDE environment.

To use the jig, you mount the dowel into the sled, install the spiral blade, and clamp the jig to the scroll saw table. Tilt the table if desired. Position the jig so that the blade enters the dowel at your chosen offset from the centerline. Then you start the scroll saw and initiate your program on the computer that is connected to the Arduino. The program contains your desired parameters of pitch, cutting speed, and length of the cut.

Step 3: Centerline Cut

If you cut the dowel along its center line, you get two pieces which thread around each other beautifully. To get a center cut started drill a pilot hole through the dowel about 1/2" from the starting edge, then position the jig and insert the scroll saw blade through this hole.

Use hardwood like walnut, cherry, maple, etc. to create a strong spiral set. Poplar dowels are cheap and will work, but they can be more fragile. I have used dowels from 1/2" to 1.5" in diameter.

The dowel may be round, square, rectangular, hexagonal, or octagonal. A square-dowel center-cut spiral will be very confusing to people, because it looks like ‘it should not unscrew’. But it will! It’s a pretty cool toy to play with.

Step 4: Offset Cuts

By making cuts that are offset from the dowel center axis you can ‘slice off’ several spirals that wrap around a center spiral ’screw’. My jig can handle dowels up to 1.5 inches in diameter and 10 inches long. I have been able to cut four outside spirals, one inside spiral, and a center spiral screw. That is six separate pieces wrapped around each other! The resulting wood spirals are a little fragile and should be handled carefully.

Step 5: Angled Cuts

You can tilt the scroll saw table to get even more variations on the shape and look of the spirals.

A special case occurs if you tilt the table so that the blade enters and exits the same cut line. That tilt angle depends on the offset from the dowel centerline, the dowel diameter, and the pitch. The math gets complicated but I worked it out. For example, a 5/16" offset on a 1-1/4" dowel with a 0.8 inch per revolution pitch needs a 25.3 degree table tilt to meet this requirement. The offset parameter is difficult to set accurately, and the results are very sensitive to the offset; so some trial and error is advised. The result is a beautiful set of nested spirals like these.

Step 6: Dowels

You can make your own dowels from hardwood boards.

My dowels are 12 inch long, resulting in 10 inch long spirals. Some wood species cut smoother than others. Poplar, maple, cherry, and walnut cut really well. Pine and oak do not work well with the #0 blades; they leave a jagged/uneven edge and you may not be able to separate the spiral pieces. In that case use #2 or #4 blades for a more aggressive cut and larger kerf. Avoid wood pieces with knots.

You can add interesting designs by laminating different colored woods. Cut your dowel blanks on the table saw to make a square, rectangular, hexagonal, or octagonal cross section; or turn round on a lathe. Then cut your spirals; the results will look amazing!

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60 Comments

I really like the complexity of this project. And, the results are extraordinary. But, is there an actual use for this type of jigging? Maybe a wooden screw type actuator? Don't get me wrong I dig this and all. I'm just curious to know if this is useful for something or another?

1 reply

Thanks for your interest. For me, the project is purely artistic/aesthetic; for the intellectually curious. The resulting spirals are fun to play with, and almost everyone tries to figure out how they were made. They won't work well as a screw actuator; too much play and probably too fragile. You could use them for ornamental accents on furniture, or on wood carvings, plaques, displays.

Love it!

How about having two types of word dowels of the same size and cut that are spiraled together? Would make for some really cool table legs if you could make them long enough.

Would love to have details on making the necessary jig and controls.

9 replies

The first and second picture in Step 3 show what you are suggesting. Note that the oak and walnut dowels were cut the same, and fit into each other as in the second picture, top. You won't be able to glue them back together, the kerf (gap) is too much to make a good glue joint. Maybe you could use epoxy??

1-1/2 inch diameter is the max I can do, even at that the scroll saw is challenged. Making the spirals longer is also tricky. When you cut about 4 to 5 inches into the dowel it starts to flex and vibrate quite a bit from lack of support and resonant frequencies. This would be worse with a longer dowel.

The two dowels at slightly different cuts, about a saw width different so that one is cut on the 'inside' of the line and the other on the 'outside' of the line.

Thanks loads for the update. Sorry I did not see those images initially. Was too intent on the instruction I guess.

What if you use a larger dowel of 2" and bore it out first? You could then use a metal rod down the center for the actual support structure when finished.

Black epoxy would look cool in the gaps for glueing the two pieces together.

Also on your jig could you add rollers top, bottom and sides near the saw blade that would minimize the amount of flex? These would need to be on the uncut side.

Sorry. Don't mean to belabor the discussion of longer pieces. It just adds really cool furniture possibilities.

Anyhoo thanks again for the Ible'! If you do get around to making the Ible' for the fixture setup that would be great.

David

You could apply all the suggestions you made in the design of the cutting jig. Cutting a 2 inch diameter dowel may be beyond the scroll saw capability; on the other hand if you had a hollow core like you are suggesting that might work. You would have to think about how to mount the two ends securely. You will still run into problems with vibration/flexing. Essentially you are cutting a ‘spring’ that likes to flex.

The best support for a round dowel is a long board with a v-groove. Mount that board between the scroll saw table and the dowel. Obviously, that will not work for square dowels.

If you construct a table leg with a metal rod in the center you can stack a bunch of 5” to 10” spiral sections around it to achieve the length you want; the joints would be pretty much invisible. Let me know if you make any and how they turn out.

Just a thought on the support for the helix as it is cutting, could you have the "springs" feeding into a tube & feeding from a tube, to give extra support to prevent as much ability for them to flex once cut? E.g. 1 & 1/16 inch internal diameter pipe & 1 inch dowel?

I'm not much for these technical kind of things, but the thought popped in my head while reading through the comments section.

Great instructable & nice finished pieces.

That might work somewhat, but the tube would be cut by the blade along with the dowel. You would still have support on the uncut portion of the dowel.

I was actually meaning 2 separate pieces of tube. One on the "after-cut" side of blade & one on the "before-cut" side of blade. They would have to be fixed in place (so not moving when the dowel moves) so that they could remain at the same distances from the blade. Although, that begs the question how would the dowel be held in place then/pushed into the blade...

Yes, it would be complicated.

look up lathe steady rest. You put a wheel attached to the scroll saw table just before the cut area to prevent bowing and vibration.

Great Instructable.

I showed it to my dad, and now he wants to try to build a similar jig. We have a cnc that we built a few years ago, so we should be able to drive the steppers from LinuxCNC. It should be as simple as 1 gcode (G01, I think).

I also put together a Mathematica program to model the cut based on the radius, offset, pitch and angle (I am a math grad student by day).

If you do get around to making an instructable on the jig itself, that would be awesome. Otherwise, any tips that you might have on building would be appreciated. My dad's first instinct was to try to build it bigger, but after reading some of your comments about the vibration issues, I think we build ours to a similar scale.

Thanks

1 reply

Thanks for your comment.

I am working on an Instructable for the Spiral Cutting Jig but it will take me a while. I want to rebuild my jig and document the build.

For the programming I am using the Arduino IDE, and the examples that come with the Big Easy Stepper Motor Driver get you 95% to your final program. It does not involve gcode, you basically tell the stepper motors: turn some steps on the spindle motor, wait, turn the dowel motor one step, wait, repeat! LinuxCNC and gcode should work fine as well.

I build the ‘gear box’ - i.e. the motor/pulley mounts from 3mm clear acrylic cut on a laser cutter. The jig uses several brass bushings, stainless steel couplings, timing belt(10”) and pulleys, and 1/4” nuts and bolts. The jig header is 3/4” baltic birch plywood, the body is particle board and MDF(because I had some - baltic birch would be better throughout), and maple cross pieces.

It would be great if you could share your Mathematica program as a stand-alone app; don’t know if that’s possible.

Here is a link to a movie clip showing the vibration/flexing, both in real time and slo-mo.

https://youtu.be/TZGwNO5fTgA

It’s hard to avoid vibration, and it becomes worse for longer cuts and smaller (tighter) pitch. The dowel in the movie is 22mm by 30mm with a pitch of 1.5 inches (Yes, I know, I’m mixing units!), being cut along its center axis. It turned out ok despite the flexing. If you try to dampen the vibration with you fingers you probably make things worse by deviating the cut, and the pieces will not unscrew. So I ignore the vibration. Some cuts have very little vibration, it depends on the wood and wood grain, the lamination, the pitch, and the diameter and offset from center. And sometimes things fail.

Beautifull. I will make one. Please publish the arduino sketch.

Roy

These are amazing! Very interested in the automation side of this. What motors (specs) did you choose?

2 replies

That's great help, thank you!

Amazing!

Really clever idea, (and execution)