This design was inspired by a request posted to the ATMakers.org page on Facebook for a way to make a capacitive stylus that could be used by people with limited finger and hand control. When I asked the poster to describe the device further I was pointed to a commercial device available on Amazon called the Sixth Digit by Handizap Capacitive Touchscreen Finger Stylus Ring. I read through the comments of customers who had purchased the product and found that there were some fundamental issues with the design:

“Couldn’t get them to stop rotating around my finger and you can’t squeeze them to tight because it’ll cut the circulation off in you pinky finger. Just the little bit I did use them I noticed that whatever the tip was made of it had already started to wear out pretty fast.”
“Worthless. They spin around your finger. At 2 for $30 I laughed at myself at how I got ripped off. Looks like something you would get out of a gumball machine. Don’t waste your money.”
“Good idea but ring won’t stay tight on finger”

This design involves mounting the stylus to two or three fingers to prevent the rotation. It’s also possible to find high quality capacitive tips for about $1 apiece. In order for the stylus to work properly, there needs to be an electrical connection between the capacitive tip and the user’s skin. This can be accomplished in one of two ways – either with a nut and bolt or using a conductive filament like the conductive PLA from ProtoPasta. Both solutions work well and cost about the same – $1.00 to $1.50 per stylus, which is a savings of about $12 over the commercial product.

The bolted stylus requires a 5 mm hex head bolt and a coupling nut [The length of the bolt depends on the length of the desired stylus.] The conductive stylus doesn’t require any hardware (though a single 4 mm nut can help stabilize the capacitive tip) and the post can be arbitrarily long (or short).

For greater customization, the post of the stylus is a separate component as is each of the finger/toe rings – so each component can be printed using of a differently colored filament and each ring can have a different diameter to better fit the user’s fingers. Finally, you have the option of printing the entire stylus or just the finger rings portion as a solid unit. A solid stylus is easier to print, sturdier, and allows the users fingers to be closer together.

First Things, First:

To create your custom stylus, you will use the free software called OpenSCAD from OpenSCAD.org. [Instructions for downloading and installing OpenSCAD on your computer can be found here.]

Next, download the stylus designer from the Printables website. In particular, download the file called “6th_finger_and_toe_stylus.scad” and open it with OpenSCAD. You’ll find another file there called “bolt.stl”. That object is part of the stylus mount, which is optional. The bolt part of the mount is always the same so you can save time by downloading the STL file rather than creating it from scratch.

Second Things Second:

At the most basic level you need to decide if you’re creating a 6th finger stylus or a 6th toe stylus. You also need to decide where the tablet or smartphone will be located relative to your hand or foot. That will affect the orientation of the stylus.

For example, if your phone or tablet will be located below your hand, you will probably want a stylus design similar to this:

If your phone or tablet will be located below your foot, you will probably want a stylus design similar to this:

If your phone or tablet will be located out in front of your hand and you will hold the stylus with a clamped hand, you will probably want a stylus design similar to this:

Note that the above image shows three rings but a two-ring stylus might instead be appropriate.

You have at least two options for the filament that you use to print your stylus. Normal PLA is very common, and you might have lots of it on hand in lots of different colors. It’s also fairly inexpensive but it’s not a very good conductor and there has to be a way to conduct a small amount of electricity from the capacitive tips that you purchased to the user’s skin. You can get around the fact that normal PLA isn’t a very good conductor by inserting a small metal bolt through the center of the stylus to hold it together and to conduct the electricity. All of the above images represent styli that incorporate a bolt and nut to conduct electricity from the stylus tip to the user’s skin. The length of the stylus depends on the length of the bolt.

On the other hand it’s possible to purchase “conductive” PLA. It’s about 5 times more expensive than normal PLA and only comes in black (so far). You can purchase small amounts (see the link above to purchase a 125 gram coil for $15). That’s enough to print over 50 styli so it’s plenty of filament, but the fact that it’s just a loose coil and not on a spool can make it a pain to use. On the other hand it’s really easy to assemble a stylus made with conductive filament and the stylus can be arbitrarily long because it’s not limited by the size of the bolt.

In the above image, the conductive filament is the black layer. You can save money by printing your stylus as a “sandwich” with standard PLA on the outside and conductive filament in the middle. It’s also a way to create a “personalized stylus”. The above stylus was printed for a Denver Broncos fan.

You may need an alternative angle of the stylus tip to the finger rings, like this:

Note that such a stylus has to be printed entirely or at least halfway with conductive filament since it doesn’t provide a way for a bolt to come in contact with skin.

The following video shows a very long stylus made of conductive filament in action:

You can screw the capacitive tip directly into the plastic tip of the stylus or you can add a 4 mm nut to the design. In that case, the capacitive tip screws into the nut producing a much stronger attachment:

If you’re interested in how a capacitive pointer/stylus works, you can read more about it here.

Third Things Third:

The next step is to gather all the non-printed components.

If you’re going to use conductive filament then (in addition to obtaining the filament itself) you may want to purchase a single M5 x 4 mm hex (or square) nut.

If you’re going to be using normal PLA then you’ll need a M5 hex head bolt between 20 and 80 mm in length. You will also need a M5 mm hex coupling nut – either 8 mm or 15 mm in length. For the most part, choose the coupling nut that is easiest for you to get but the longer nut gives you a slightly longer stylus given the same length bolt.

In either case, you’ll need to purchase a capacitive tip. The Amazon link is a decent deal but any tip with a 5 mm threaded post will work. [You may find tips sized 5 mm, 6 mm, and 7 mm – these dimensions are for the base of the tip and not the threaded post which is 5 mm in all cases.]

Forth Things Forth:

You now need to choose the right components to print.

Begin by deciding which fingers or toes you want to use to control the stylus. Then print a pair of measuring rings to help you measure the diameter of these fingers or toes. The ring should push all the way onto the finger or toe and comfortably clear each knuckle. Also measure the length of the last joint of the finger/toe (closest to the palm or sole of the foot). This measurement will be the value you choose for ring width. The wider the ring the more stability it will offer.

Now determine how far away from the hand or the foot that the tablet or phone will be placed. Don’t include any distance that will be covered by extending the arm or leg. What’s left is the length you will need your stylus to reach. Distances longer than 90 mm will be difficult to reach with a bolted stylus. In that case you need to purchase conductive filament and create a conductive stylus.

Finally, determine which tip and rings you will need to assemble and how they will be assembled. A stylus will be comprised of a stylus tip, a stylus ring, one or more finger/toe rings and, optionally, a stylus extender (only possible with conductive filament).

There are three methods for assembling your stylus:

entirely with dovetail joints,
as an entirely solid unit, or
as a solid set of rings to which a stylus tip is attached via a dovetail joint.

If you’d like to experiment with different ring configurations and different size rings, using dovetail joints works best. Then, once you’re comfortable that all the rings are arranged in the right sizes and orientation, you can create a solid stylus which is more sturdy and will allow your fingers to rest more closely together. You can separately determine if the stylus tip should be solidly attached to the finger rings or if it should be removable and joined later, as needed, via a dovetail joint.

We recommend that you start with dovetail joints while determining the best fit and then switch over to the one of the two “solid” types before printing. If you’re creating a nut & bolt stylus, the stylus tip must be separately joined to the stylus rings which can be solid.

The instructions below describe how to create a stylus and assemble it using dovetails. Following those instructions you’ll learn how to turn that design into a solid stylus or a solid set of rings (to which a stylus will be attached).

Stylus Ring

You will need only one stylus ring. The stylus ring comes in several forms depending on how you want to mount the finger/toe ring(s):

Both the “A” and “B” stylus rings have a “type” value of “one finger ring”. The type “A” stylus ring has a stylus tip mount angle of 90 degrees while the type “B” stylus ring has a stylus tip mount angle of 180 degrees but you can choose other angles (more about adjusting the mount angle later). The type “C” stylus ring has a “type” value of “two finger rings” and the two finger rings always sit opposite of each other.

The conduction type for your stylus will have an effect on how the stylus attachment point of the stylus ring will look:

If you’re creating a bolt and nut type of stylus, the stylus ring will have a cut out for the head of the bolt where the stylus mounts. If you’re creating a conductive filament stylus the mount for the stylus on the stylus ring will be a simple dove-tail joint just like the mounts for the finger/toe rings.

Finger/Toe Ring(s)

There are two types of finger/toe rings:

Finger/toe rings connect to the stylus ring and provide extra stability. The more finger rings you add, the more stability you will have – but the harder it will be to put the stylus on to your hand because you’ll have to jump through more hoops (so to speak…).

The type “A” finger/toe ring is called “single finger ring”, and the type “B” finger/toe ring is called “mount for second finger ring” (because you’ll be adding a second finger ring to this one). Using a series of type “B” finger/toe rings, you can have a virtually unlimited number of rings. Note, this option only applies to a stylus assembled entirely with dovetails.

Splitting a Ring

When you put on the stylus, the rings will have to slide past your knuckles but will, in the end, probably sit on the part of your finger closest to your palm. If your knuckles are larger than the part of your fingers where the stylus will rest, specifying a ring diameter that fits over your knuckles may result in a stylus that is too loose. You can mitigate the problem a little by putting a split in the ring and sizing it a bit smaller than your knuckle diameter. The split will allow the ring to expand slightly when it slides over your knuckles and then spring back. Don’t size the ring so small that you are pinched by the split in the ring.

Rings are solid by default. To add a split choose “yes” from the “split ring” pull-down in the “Sixth Finger/Toe Ring Info” section:

Note that you make the decision to split or not to split for each ring.

To produce this conductive stylus:

You would need to print:

a stylus tip for a conductive filament type of stylus that has a cut-out for a 4 mm nut,
a stylus ring for “one finger ring” and a stylus tip mount angle of 180 degrees , and
a “single finger ring” finger ring.

To produce this bolted stylus:

You would need to print:

a stylus tip for a bolt and nut type of stylus with a cut-out for an 8 mm coupling nut
a “two finger rings” stylus ring, and
two “single finger ring” finger rings.

Fifth Things Fifth:

Let’s look at how the user interface is designed to help you customize and create these components.

The customization options are organized into several sections:

The Parts and Assembly section is where you indicate how you will be assembling your stylus and which part of the stylus you’d like to design and print along with several settings that affect many aspects of the stylus.

The Stylus Info section is where you make general decisions about the stylus like its width and the way that the capacitive tip will be electrically connected to the user’s skin.

If you’re designing a stylus with conductive filament, the Conductive Stylus Info section is where you provide more specific information like the length of the stylus and whether the capacitive tip will be mounted to the stylus with a 4 mm nut. On the other hand, if you’re designing a stylus with a bolt and nut, the Bolted Stylus Info section is where you provide information about the bolt and the coupling nut.

The Ring Info section is where you provide detailed information about each ring you need.

The Solid Stylus Info section is where you record values that you set for the diameters of each of your rings and their relative orientation so that the designer can create a single, unified design for your stylus.

As you specify each stylus part that you need, start at the top of the set of categories and work downward. Begin with choosing the method of assembly and then the particular part that you want to design/print. It will be helpful to see the part displayed in the user interface as you provide more specific details. The display will update to reflect each change that you make.

The Mount Info section is where you provide information needed to design a mount for your stylus that you can attach to your desk, table, or chair and can help you put the stylus onto your hand and remove it later.

PartS and Assembly Section

This section focuses on options that affect the stylus as a whole, as well as helping you select a stylus part to render and print, and determine how those parts will fit together.

As described above, there are three methods for assembling your stylus:

The “part to print” pull-down list contains all possible parts that you can print (as well as what part will be shown in the display pane of OpenSCAD:

You will need to print a stylus tip, stylus ring and at least one finger/toe ring for any stylus. You can also print a stylus extender for a conductive filament type of stylus if you need a stylus that is longer than the longest possible stylus tip.

Stylus tip is selected by default. You will see an image like this in the display pane:

It has a particular shape and length based on other default values. You can modify these values as you continue with your design and the display will update to reflect each change.

The “solid stylus” part is a combination of all rings and possibly the stylus tip as well. More on that option below.

The last three items: holster, mount, and mounting bolt are optional and used to hold your stylus nearby. It can also support you in getting the stylus on and off of your hand or foot.

Note that the “ring width” and “ring thickness” values you put in this section will apply to all rings.

The remaining options are discussed below.

Stylus Info Section

The Stylus Info section has two options. The first is called stylus width. The starting value is 10 mm but you can make the stylus thinner or thicker. A thinner stylus will be lighter but slightly more fragile. Also a conductive filament stylus that is thinner than 10 mm won’t support an opening for a 4 mm mounting nut. At the same time, a thick stylus may be cumbersome for a small user.

The second option is where you determine the conduction type for your stylus. The starting value is “bolt and nut”. If you change the value to “conductive filament” the image of the stylus tip will change in several ways:

The hole for a mounting nut disappeared (for now) and a dove-tail joint was added to the back end. It also shrunk in length because a conductive stylus doesn’t, necessarily, require a mounting bolt – so it can be shorter. You can easily make it longer if you’d like.

Conductive Stylus Info Section

The Conductive Stylus Info section provides the final details about your stylus that are specific to a conductive filament style stylus.

The starting value for the length of the stylus tip (or an, optional, stylus extender) is 20 mm. You can only have one stylus tip but you can have an unlimited number of stylus extenders. Each of them can be up to 200 mm long. The longer the stylus, the more unwieldy it becomes. Still, if you need a very long stylus, then you can design one.

If you want to add a 4 mm nut to mount the capacitive tip more sturdily select yes from the “use 4 mm nut to mount tip” pull-down list.

Setting the length to 50 and using a nut changes the image to look like this:

A slot has been created for the nut and the stylus tip is longer.

Bolted Stylus Info Section

The Bolted Stylus Info section is where you provide information specific to a bolt and nut style of stylus. This category is only relevant if you choose “bolt and nut” as the “conduction type” option in the Stylus Info category.

You’ll see that there’s no place for you to specify the length of your stylus. That’s because the length of the stylus is completely dependent on the length of the bolt you choose and the length of the coupling nut.

If you choose an 8 mm coupling nut, then the stylus will be 5 mm longer than the bolt you use. If you choose a 15 mm coupling nut, then the stylus will be 10 mm longer than the bolt you use.

Both of these stylus tips use a 30 mm bolt. The first uses an 8 mm coupling nut:

The second uses a 15 mm coupling nut:

Now render your design and export it as an STL file. Name the file “stylus tip.stl”

Once you have the stylus tip/extender you want, it’s time to specify the stylus ring and finger/toe ring(s).

Ring Info

You will specify the stylus ring and finger/toe ring(s) separately. Go back to the Parts and Assembly section and choose “stylus ring” from the “part to print” pull-down list. The information you’ve provided up to this point will impact what you see but it may look something like this:

The ring has an inside diameter of 20 mm and it’s 10 mm wide. The stylus mount is cut to accept the head of an M5 hex-head bolt and it has a mount for a finger/toe ring on the opposite side of the ring. If you chose a conductive filament type of stylus, the stylus mount will look different.

Use the measurements you took earlier to size the ring and choose a value from the “stylus ring type” pull-down list based on the kind of 6th Finger/Toe Stylus you want to create. You can increase the thickness of the band for a stronger ring. The “ring width” and “ring thickness” options are located in the Parts and Assembly section and affect every ring.

In the Parts and Assembly section, choose the angle you’d like to have between the stylus tip and the second ring. The option is called “stylus tip mount angle” and the default value is 180 degrees – meaning that the stylus tip and second ring are directly across from each other. A value less than 180 degrees, angles the tip a bit so that it accommodates the angle of your hand:

This stylus ring has a “stylus tip mount angle” of 160 degrees.

Finally, choose the attachment angle between the stylus ring and the stylus tip. In the picture above, the attachment angle is 0 degrees – meaning that the tip and the rings are all in the same plane. If you instead choose an angle of 90 degrees you can create a stylus where the stylus tip and the rings are at a right angle to each other:

Setting the “stylus tip mount angle” won’t have any effect on a 90-degree stylus with two finger rings.

Now render the design for your stylus ring and export it as an STL file. Call the file “stylus ring.stl” Also, record the ring size for the stylus ring. It will be important later if you decide to create a “solid” stylus.

You need to create at least one finger/ ring so choose “finger/toe ring” from the “part” pull-down list of the Part to Print category.

You’ll need at least one of these simple finger/toe rings. If you want to link two or more finger/toe rings together you’ll also need one with a mount for a second finger/toe ring:

Choose an appropriate value for diameter of each ring, The ring width and thickness will be the same as that for the stylus ring.

Now render the design for your finger ring and export it as an STL file. Call the file “finger-toe ring 1.stl” for the ring that will attach first to the stylus ring (or to the left of the stylus ring). If your design involves a second finger ring, save that STL file with the name “finger-toe ring 2.stl” Also, record the ring size for each of the finger rings. Those values will be important later if you decide to create a “solid” stylus.

Sixth Things Sixth (assembling your stylus):

The following video shows you how to assemble, both a bolted stylus and a conductive stylus:

That’s it! Put the stylus on your hand or foot and try it out!

Create a solid stylus

You can turn your design into a single, solid device or fuse together just the rings together and allow the stylus tip to be swapped out and attached using a dovetail joint. A solid stylus has several advantages. It’s sturdier so the rings can be thinner. It’s easier to print because more of the device is in contact with the build surface at any point in time. Finally, if you have smaller hands or if your fingers simply don’t want to spread apart far enough for the two parts of the dovetail joint to come together, a solid stylus eliminates this extra distance.

Note that a solid stylus can’t include more than two finger/toe rings.

You create a solid stylus by choosing either “all solid” or “solid rings” from the “assembly type” pull-down list in the Parts and Assembly section. You’ll also need to set values for the options in the Solid Stylus Info section:

Remember how you were asked to record the diameter of each ring when you created their STL files? This is where you’ll be entering that information in order to create a solid stylus. You’ll also tell the designer how many finger rings are in your stylus.

The designer then goes off and assembles the STL files you’ve already created into a single object. It looks for a file called “stylus ring.stl” and attaches the contents of a file called “stylus tip.stl” to one end of the ring.

The contents of a file called “finger-toe ring 1.stl” is connected to the stylus ring directly on the left if you have a two ring design or at the location you specified in “stylus tip mount angle” if you have just one finger/toe ring.

If you set “number of finger toe rings” to “2” the designer will look for another file called “finger-toe ring 2.stl” and put that ring to the right of the stylus ring.

But Wait! The designer just grabs what ever if finds in these STL files and jams them together. If you’ve created your rings with dovetails, the dovetails aren’t used in a solid stylus so you’ll see something like this (“assembly type” set to “solid rings”):

Go back, set the “assembly type” option to “all solid” or “solid rings”, as appropriate, set “part to print” as “stylus ring” and then as “finger toe ring”, quickly re-render and save your rings – with the proper names.

Come back and set “part to print” as “solid stylus” and you’ll see what you expected:

Watch the Stylus in Action!

Here are two videos that show the sixth-finger stylus and the sixth-toe stylus in action:

Mounting Your Stylus

You can print a mount for your stylus. You can locate the mount close to where you normally use the stylus. This will help you keep track of your stylus and the mount can aid you in putting the stylus on your hand and taking it off.

The mount is comprised of three parts:

The holster holds your stylus a and slides into an opening in the top of the mount. The mount is sized to fit the shelf or desk that you will attach it to. the mounting bolt provides some stability once the mount is attached with double-sided, foam tape.

The options for designing your mount are located in the Mount Info section:

The first three options control the design of the holster:

stylus tip diameter – the holster will have a hole at the bottom that will allow the capacitive stylus tip to pass through to protect it from wear. Measure the diameter of your tip as shown below.

holster opening height and diameter – the shaft of the holster will be sized based on the dimensions of your stylus but that still leaves the funnel at the top:

The wider the opening the more help you will get in returning your stylus to the holster. At the same time, the wider the opening, the shallower the angle of the funnel will be and the harder it will be to print the holster without using supports. You can compensate for a wide opening by increasing the height of the opening.

shelf thickness – this is the thickness of the desk or shelf that you want to attach the mounting system to. The mount will be designed with an opening that is 5 mm wider than the value you provide. That leaves enough room for you to add one or two layers of double-sided, foam tape. What ever space is left over will be taken up with the mounting bolt

Note: The bolt is intended only to hold the mount in place while the foam tape settles in. Don’t over-tighten the bolt.

jaw length – adjusting this value will change the length of the upper and lower “jaws” of the mount and will affect how much contact the mount will make with your desk/shelf.

While you can generate the mounting bolt using the program, it will always be the same bolt. And since the bolt can take several minutes to render, you can simply download the same STL directly from Printables (along with the .scad file) and just print it.

This video will show you how to assemble and attach your mount. It will also demonstrate how the mounting system will help you put on and take off your stylus, one-handed:

I’d like to offer a special thanks to Jason for creating these two videos demonstrating his use of the 6th Finger/Toe stylus:

Do you have any ideas about how to improve this design? Provide some information below: