Incredible Wooden Spirals

You can cut incredible nested spirals with a scroll saw. Spirals in a spiral, if you will. They are really cool toys or art objects and I have always been fascinated by them. You can make two, three, and even more spirals to interlock each other creating your own double helix (or triple helix ... ). A few years ago I made a jig to cut these spirals, and since then I have been asked many times: "How do you make the spirals?" .

So I have decided to rebuild my spiral cutting jig in a more professional way and show you my new version using standard CNC parts and technology.

Here is a link to my original Instructable: https://www.instructables.com/Nested-Helix/

The idea for this wooden spiral cutting technique was first published by Steve Garrison.

The CNC parts I used were purchased from Openbuilds and Zyltech. Other companies offer similar parts and components, so use your preferred vendors. I have no financial or professional relationship to any vendor mentioned.

• OpenBuilds

https://openbuildspartstore.com/c-beam-linear-actu...

Linear actuator, cables, metric screws and nuts, spacers, corner connectors, V-slot extrusions, 2nd gantry assembly, NEMA 23 stepper motors

• Zyltech

https://www.zyltech.com/

Arduino, CNC shield, stepper motor drivers, 24V power supply

• Bushings, https://www.lowes.com/pd/Hillman-1-Count-1-4-in-B...
• Shaft coupler 1/4" to 1/4", https://www.sparkfun.com/products/12251
• Scroll Saw Blades: Olson #2 and #4 Spiral Blades, https://www.olsonsaw.net/cat/scroll-saw-blades/
• 1/2" plywood, 1/4" acrylic sheet, #8 wood screws, 3D printed gears, 3D printed hold-down clamps, 1/4"-20 bolts or threaded rod, nuts, and washers, Phillips head bit
• Wooden dowels, e.g. https://www.homedepot.com/p/6420U-1-1-4-in-x-1-1-...

Tools:

Scroll saw, table saw, drill, 1/2" Forstner drill bit, 7/32" (5mm) and 1/8" drill bits, Helpful: laser cutter, 3D printers

Here are some examples of spirals I made! Look at the video below to see how well they unwind/unscrew.

Let's start building the jig. The linear actuator is a pretty straightforward and easy build. Just follow the instruction video from OpenBuilds. I recommend to assemble and test the linear actuator first before installing any additional components. See steps below for the electronics and software I use.

Assemble a second gantry plate without an anti-backlash nut block. This second gantry is identical to the first one except it is not attached to the lead screw. Install this gantry plate in the linear actuator C-beam and check that it can move freely.

Prepare a 3" wide by 18" long piece of 1/2" thick plywood. Don't use thicker plywood or the jig won't fit under the scroll saw. On each end drill a hole pattern as shown in the pictures. A pattern template is attached. The holes are as follows: (1) 1/2" diameter shallow recess, drilled 3 mm deep, drilled with a Forstner bit, (2) 7/32" (5 mm) hole drilled through, (3) 1/8" pilot hole 1/4" deep for #8 wood screws.
The plywood strip is attached to the two gantry plates with 15mm long low-profile M5 screws. The two gantry plates and the plywood piece form a sled for moving the dowel-turning assemblies along the actuator.

Attached to the plywood sled is a motor mount assembly to turn the dowel to be cut while the gantry moves forward. Let's call this the headstock.

Mount four corner connectors with M5 - 8mm low-profile screws and Tee-nuts to a 10" long V-Slot 20x40 extrusion. The corner connectors should be mounted 100 mm and 160 mm from the end of the extrusion as shown in the pictures. Check to see that the corner connectors line up with the 1/8" pilot holes on the plywood sled. Then attach the V-Slot extrusion to the plywood sled with #8 wood screws. The V-Slot extrusion should be perpendicular to the linear actuator when installed.

Install a second identical V-Slot extrusion on the other end of the plywood sled. This is for the tailstock assembly. These dimensions allow for up to 14 inch long spirals. The tailstock 'dead center' screw can be adjusted by about +/- 0.75 inch, see step 6. If you want to cut shorter lengths of spirals you can always move the second V-Slot extrusion and tailstock assembly to a new location on the plywood sled.

Make four mounting plates for the headstock and tailstock assemblies.

I made the mounting plates from 1/4" (~6 mm) acrylic sheet cut on a laser cutter. If you don't have access to a laser cutter you can make the plates with a table/band/scroll saw and drill press. Use acrylic or 1/4" plywood. Templates for the mounting plates are attached. You need two each for the headstock and tailstock.

The two herringbone helical gears were 3D printed. Specs are 20 teeth, 1.5" pitch diameter, 1/2" thick, 1/4" axle hole. One gear has a recess to retain a 1/4" hex nut. The other gear has a flat in the 1/4" hole to fit the stepper motor axle. Files for the gears are attached.

If you don't have access to a 3D printer you can redesign the headstock assembly with a belt and pulley system.

1/4"-20 threaded rod (or bolt), washers, and nuts are used for the mounting axles for the dowel. I am using 1/4" by 3/8" bronze machine bushings instead of bearings as the rotational speeds are very slow. Attached to the 1/4" bolt is a coupling and Phillips head tip. This is the 'drive center'.

Headstock Assembly:

• Two mounting plates
• Stepper motor
• Two gears
• Four each of M5 - 65mm screws, 40mm aluminum spacer, nylon locknut
• Two 1/4" by 3/8" bushings
• 2.5" 1/4"-20 machine bolt, washers, and nuts
• 1/4" coupling and #2 Phillips head tip, shortened to fit coupling; or shape the end of the bolt to a Phillips head

Tailstock Assembly

• Two mounting plates
• Four each of M5 - 65mm screws, 40mm aluminum spacers, nylon locknuts
• Two 1/4" by 3/8" bushings
• 2.5" long 1/4"-20 machine bolt, nuts, and washers

File the end of the 1/4"-20 bolt to a point to make it a 'dead-center'.

Mount the headstock and tailstock assemblies to the V-Slot extrusions on the plywood sled with M5 screws and Tee-nuts. To do this put the linear actuator onto a flat surface and use card-stock to lift the assemblies slightly off the surface - for clearance. Also use a 1/8 " spacer between the actuator C-beam and the mounting plates for clearance. Then tighten the M5 screws. Run the linear actuator back and forth to check that everything moves properly.

This would also be a good time to calibrate the x-axis stepper motor (linear actuator) settings. See below for software and hardware settings. Start with a GRBL parameter of $100 = 400 (steps/mm), then tweak this value based on actual movement measurements. My system calibrated at 395.062 steps/mm. For reasons having to do with very low feed rates in GRBL, I choose to use half of that, i.e. $100 = 197.531 (steps/mm x-axis). This means I have to enter (desired spiral length in mm) times 2 into the software. Its a little awkward to remember.

At this time I also marked my x = 0 position with a piece of tape on the C-beam. This is useful for future reference.

For the y-axis - which is the rotation of the dowel - calibrate how many mm are needed for one revolution. For my setup it is 20 mm per revolution. Make a note of that: millimeters to enter into software equals (number of spiral turns desired) times 20. For example, 100 mm yields 5 turns. Your numbers may differ.

Finally, you need to make some brackets to attach the entire jig to the scroll saw table. I made some 3D printed angles and hooks that slide into the C-Beam extrusion. Detach the actuator end cap and slide the two angle brackets and two hooks into the appropriate slots as shown. Later on use C-clamps to fix the jig to the scroll saw table in the desired position.

The jig is controlled by an Arduino Uno, a CNC shield, stepper motor drivers, and power supply.

Follow these instructions to get the required GRBL software and upload it to the Arduino: https://github.com/grbl/grbl

The CNC shield should come with instructions. Here is the how-to for the Zyltech and similar shields: https://www.zyltech.com/arduino-cnc-shield-instru...

You need to set the micro-step jumpers for the two stepper motors. I am using a 1/16 micro-stepping setting for x and y.

Connect the linear actuator stepper to the x-axis motor driver.
Connect the dowel rotation stepper (headstock) to the y-axis motor driver.

I did not install any end/limit switches. You will have to be very careful not to run the sled/gantries into the end plates on either side of the actuator, or into the scroll saw head. Do not use the homing command in GRBL unless you install limit switches.

To be on the safe side I installed an emergency cut-off switch into the 24V power supply line to the CNC shield. It can be very useful to avoid crashes.

Use GRBL control software to cut your spirals. I am using a free program called Universal Gcode Sender (UGS).

https://winder.github.io/ugs_website/

First you should test the setup by running each of the two motors separately. Remember that the x-axis is the linear actuator advance, the y-axis is actually the rotation of the dowel.

Here are the important GRBL settings for my jig:

• $3=3 (axis directions, change this to cut left-handed or right-handed spirals)
• $22=0 (homing cycle disabled!)
• $100 = 197.531 (steps/mm x-axis, calibrated for my machine, see step7)
• $101 = 160 (steps/mm y-axis)

Below are some web resources to help with GRBL.

https://reprap.org/wiki/G-code

https://makezine.com/2016/10/24/get-to-know-your-c...

https://www.routerforums.com/attachments/grbl-inst...

https://github.com/gnea/grbl/wiki/Using-Grbl

First of all, you should only use hardwoods for any spiral. Softwoods like pine, fir, etc are simply too fragile.

Prepare a round, hexagonal, or square dowel up to 1.5 inch diameter and 14 inches long. Anything thicker than that will challenge either the scroll saw or the stepper motor or both. If the blade bends while cutting the spiral will not unscrew and separate.

I glue up square dowels from walnut, cherry, maple. Oak will work but tends to yield a rougher cut. Hickory and pecan are very hard and tend to burn the blade. Make your creations interesting by mixing different hardwoods in one dowel. Leave it square, or trim to hexagonal, or round on a lathe. Trim the ends square. You also want to sand the dowels now to your desired finish, e.g. 220 grit sanding.

Mark the center on both end faces of the dowel. Drill a shallow 1/8" pilot hole centered on one end of the dowel and insert a short #8 Phillips head screw. Drill a very shallow hole on the other end for the dead center and put a little bit of hand soap into the hole for lubrication. Mount the dowel in the spiral cutting jig. The Phillips head screw will be mounted in the drive center (headstock) of the jig. Tighten the nuts on the tailstock so that the dowel is firmly seated. With the stepper motors off check to see that the dowel turns easily while firmly mounted in the jig.

For your first cuts start with simple smaller diameter dowels, e.g. 3/4" round poplar, or 3/4" by 3/4" maple or cherry, until you get a feel for the system.

Now mount the jig on your scroll saw table so that the scroll saw blade will be aligned about 1/4" from the tailstock end of the dowel. Firmly clamp down the jig to the scroll saw table with two C-clamps on the hold-down brackets.

Start the software and reset the zero position if necessary. Do this before installing the blade in the next step!!!

Look down through the blade chuck and mark the dowel where the blade would enter. Turn the dowel by hand, drill a 1/8" hole through it at the mark, and then install the blade through it. Remember you must use a spiral blade! Apply light tension to the blade. Turn on the scroll saw at low speed and slowly adjust the tension. You are ready to cut a spiral.

You'll need to experiment to find the best scroll saw speed with minimal vibration. On my DeWalt saw I use a setting of 6 to 8. Adjust the speed during the cut to minimize vibration.
You will also need to experiment with the 'feed rate' in your program (GRBL command F) to achieve a smooth cut. A good (slow) start is F12. A smooth 300 mm (or 12") long cut thru a thick dowel may take 45 minutes or more to complete. It all depends on the wood species, the diameter of the dowel, the kerf of the spiral blade, the scroll saw speed, and the offset from the dowel center axis. Go slow! Due to the way GRBL handles very slow feed rates the lowest setting for my situation is between F9 and F11. Any F settings lower than that will have no further effect on the actual feed rate.

For smaller dowels I use a #2 spiral blade with a kerf of 0.035".

For larger dowels I use a #4 spiral blade with a kerf of 0.041".

I recommend to replace blades after one or at most two cuts.

Double-check that the scroll saw is running! To start the cut enter the x and y settings into the UGS program console, i.e the (length in mm) * 2 and the (# of turns) * 20 mm like this example:

G1 X620 Y140 F12

then push return. This will cut a 310 mm long spiral with a total of 7 turns. See calibration in Step 7. The picture shows the result on a square maple dowel. It took 52 minutes to cut, blade tension was 3, scroll saw speed 6.5 to 7.5. It separated beautifully after removing the ends. The YouTube video in the introduction shows the process for this spiral.

Be sure to know the upper limit for the x-axis (i.e. max. length of dowel). Watch out that you don't run the sled into the end of the linear actuator, or that the V-slot extrusion on the plywood sled doesn't run into the scroll saw. Cut to within 3/4 inch of the dowel end. Don't cut all the way past the tip of the screw at end of the dowel, you will break the blade!

Watch the progress to make sure that things go well, the blade doesn't break, the cut doesn't wander, and the C-clamps don't rattle loose. Adjust the scroll saw speed if you get resonant vibrations, typically once you approach the middle of the cut. You can also use soft cloth rags under the dowel to dampen vibrations. My son calls this RAG: Resonance Attenuation Guide.

When finished remove the scroll saw blade and unmount the dowel. Cut off both ends to 'free' the two interlocking spirals. Check that the two spirals unscrew easily. If they don't separate you may have to cut slower, increase blade tension, use a heavier blade, reduce vibration, cut shorter spirals, use a different piece of wood, do some sanding/shaving, etc.

With a new blade and a slow cut I find that most of the time I don't need to do any finish sanding.

If you want to have more than two interlocking spirals from the same dowel make the first cut like above, but don't unmount the dowel. Instead, remove the blade, move the jig back to the starting point (x=0), rotate the dowel, drill a new starter hole 90 degrees from the first, insert the blade, and start a new cut. Be sure to use the same x and y settings as in the first cut. The result will be four interlocking - nested - spirals, pretty incredible! Again, I have included some pictures to illustrate.

Another variation is to offset the cut from the centerline of the dowel. You will get two interlocking spirals of different "width".

You can also glue extensions into the ends of your dowel. Then make one off-center cut, unmount the dowel, remove the first spiral, remount the center piece, and make a new cut at 90, 120, or 180 degrees. Repeat, and you will end up with several outside spirals and a cool looking center piece. Lastly, cut the centerpiece along its center axis.

Tilting the scroll saw table will give you yet another interesting variation. You may end up with an 'exterior' and an 'interior' fully enclosed spiral if the lower cut line matches the upper cut.

Make some dowels from different woods glued together to create interesting patterns. This can also add to the strength of the spiral as the different woods have different grain orientation.

Prepare a dowel (spindle) on a wood lathe, with coves, beads, vees, and straight grooves; then cut your spirals from that spindle.

So now that I have built this CNC jig, what else will I do with it?

• Acrylic rod spirals
• Dremel rotary tool or router attachment for making round dowels and spindles, and thread cutting
• Hot wire foam cutting rods, spirals, spindles
• Rotary laser engraving with diode laser

Stay tuned!