Knick's Prosthetic Finger v3.5.5

by knick, published

Knick's Prosthetic Finger v3.5.5 by knick Feb 14, 2016

Design Tools


A part of these Groups

View All

Use This Project

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag.

Print Thing Tag

Thing Statistics

14486Views 3615Downloads Found in Robotics


Version 3.5.5, of Knick's prosthetic finger. Find more info at my site, http://dangercreations.com

Recent Updates

-6/28/2016: Socket refinements, minor bug fixes
-6/27/2016: Found workarounds for two configurator bugs, and uploaded version with new parameters that match the measurement guide exactly. Fixed another weird issue with plugs and sockets sometimes not forming right. Also fixed configurator issue that folks had reported with 1 knuckle. The configurator now generates all parts at once, but a couple parts aren't used for 1 knuckle, causing errors. It now generates a dummy STL to avoid the error.

-6/17/2016: Created a measurement guide, find the PDF in the files/downloads section.


This 3d printable prosthetic finger ideal for those missing two finger segments, though it can be configured for either 2 or 1 knuckles. Open it with the configurator to enter your own values and generate a custom model. Many options are configurable, so with the right measurements and tweaking it should be adaptable to most people's needs - though it takes some trial and error to get a perfect fit. See the measurement guide PDF for instructions on measuring and configuring the model.

Designed from scratch in OpenSCAD, it's about 1400 lines of carefully written code. There are a lot more settings that are hidden, so if you really want to tweak - download OpenSCAD and the latest .scad file from here.


Update: 6/3/2016 :
Fixed where several settings couldn't be seen in configurator, due to some spurious comments which seem to be causing problems after a recent site update. Also added some more description for variables.

Update: 4/2/2016 :
Version 3.5.1 fixed something weird that happened to the hinge plugs, where they sometimes rendered misshapen. I updated both the STL and the openscad customizer. Also made a couple small parametric fixes and little improvements.

Initial upload

Print Settings


Flashforce Creator Pro clone






0.1 (or finest possible)




Print items slowly and at best accuracy your printer can, it's worth it to get things fitting together best.

I use Simplify3D, and generally print everything with supports, 0.1mm layers, 80% infill, 4 layers on top and bottom, 3 on sides, at 20mm/s.

I've started to print sockets with thicker layers and a .6mm nozzle, which is much faster. For the moving parts where accuracy is more important, I use a .3mm nozzle and 0.1 to 0.15 layers.


I use PLA for the hard items - the two knuckles, middle section, and linkage. In this example, I used http://www.amazon.com/gp/product/B00GTY3Z9E

Use something flexible for the socket, tip cover, hinge plugs, and bumper. In this case I used elastic TPU: http://www.amazon.com/gp/product/B00TI3JUSI

Another good option is Ninjaflex: http://www.amazon.com/gp/product/B00HSEWKSQ


Required Hardware

You'll need a few things that are not 3d printable.

- Strong (100lb) braided fishing line
- 1mm Elastic cord

Strongly Encouraged:
- Metal knuckle pins

If you cannot get the metal pins, there are two alternatives. Nearly as good, you can use 2mm aluminum wire, like this: http://www.amazon.com/gp/product/B003LTGS4E It's quite soft, so I carefully straighten it with parallel-jaw pliers after cutting.
If you're really desperate, you can use a short length of PLA or ABS filament, but it isn't nearly as smooth.

- M2.5x3mm Set screws

If you don't have these (or aren't good with teeny parts), you can tie knots instead of using set screws. It's a lot tougher to get the tension perfect this way, and you can't adjust it after -you need to restring it.

100lb Fishing line, 1mm elastic cord, 2x12mm steel pins, and m2.5x3mm slotted set screws.

Required Tools


- Small drill and/or Dremel
- Small Drill bits
I use a 1mm for cleaning holes, a 1.75mm for the set screws, and a 2mm for the pins.

- Needle Files
At least a small flat one for smoothing the inside of the hinges. I also like the round ones for getting burrs out of the tunnels.

- Sanding block or large metal file
Use for smoothing the sides of the middle segment, and for bigger cleanup depending on your print accuracy.

- Digital Micrometer
For measuring yourself for the model, checking drill bit sizes, etc.

- Adjustable temp soldering iron
I like these for smoothing certain areas, and may be needed to weld the bumper in place (depending on how elastic your material is. I can stretch it over with Ninjaflex, but need to cut and weld it with Sainsmart/generic elastic TPU).

- Eyeglass screwdriver
For the little set screws, if used.

Other tools, as needed:

- Wire trimmers
- Parallel jaw pliers
- Exacto knife and hobby pad

All the tools I use to build one. Described in tools section in more detail.

Assembly Instructions

Follow along with the written instructions below.


Read these along with the accompanying 8min how-to video, above. I give time offsets to make it easier to follow along. Original link: https://youtu.be/2EEjio4TvL8

1. Cleanup and check (0:25)

Clear support material. Spot check to make sure everything printed well and fits together. The PLA parts should barely be able to squeeze tightly together. If the hinges are already loose, or so tight you cant force them on, something is wrong. You'll smooth these later.

I use a 1mm bit to start with on the tunnels, and then smooth the elastic tunnels with a 1.75mm bit.

2. Drill the hinge-pin holes (0:38)

Drill the pin hinge pin holes with a 2mm bit, on both knuckles and the middle section. The pins should push in smoothly and easily, but not sloppy.

3. Smooth the hinge insides (0:53)

Using a needle file, lightly sand and smooth the the built-in washer on the insides of each knuckle. It should should still protrude, this minimizes hinge friction. You don't want the joints to be sloppy, so just a little at a time.

Alternate working on the inside of the hinge and the sides of the middle segment just enough until they fit very smoothly together. The middle segment end with two holes faces the tip. The side toward the base only has one hole.

4. Pre-assemble the hinges. (1:27)

Pre-assemble the 3 PLA parts and ensure that they all work smoothly together. Push the pins (or wire) through the hinge holes, ensure it's long enough to make it all the way through both sides of the hinge.

It should take nearly zero friction to move the segments across their full travel - if you can't fully articulate the finger using only gravity, then keep working at it with the files until you can - or else it won't work well later.

5. Install the set-screws (1:45)

Each of the two lengths of elastic has a knot on one end, and a set screw on the other.

You'll need to get the set-screw holes just to the right size. Too small and the screw will be hard to turn, and can crack the plastic. Too big and it will slip out - a 1.75mm bit works about right for me. You might want to practice on a scrap piece.

6. String the elastic (2:14)

For the tip, run it through whichever way is easiest. I sometimes use a small drill bit or length of wire to help me push it through. Tie a tight triple square knot on the end that protrudes from the bottom of the middle segment. Trim it neatly, and it should pull flush. For now leave a couple inches on the other side.

For the base, I use a double knot on the side coming out of the end of the middle segment, in the gap of the tip hinge. It will sink down flush. If it pulls through easily, try again with a triple knot. Then on the base the elastic will protrude in the socket area with a set screw.

7. Tighten set-screw to create tension (4:15)

Put slight tension on the elastic cord and carefully tighten the set screws to hold in place. You'll want the base knuckle just barely tight enough to pull itself fully closed. The tip should have slightly more tension, to compensate for the additional leverage that it has. trim all but a small amount on both sides, for later adjustment.

If you're not using set-screws, you'll need to tie knots on both sides of the elastic. I find it easiest to stretch to the desired tension and then mark the elastic with a bright paint marker. This way as you're tying the knot you can get it just at the right spot.

8. Install the hinge Plugs. (4:25)

I warm the hinge plugs on my coffee warmer for a while, making them soft and easier to squeeze into the ends to hold the pins in place. You should now have fully assembled hinges.

9. String the fishing line "tendon" (5:23)

String the fishing line through the tip, down under the middle section, and back up through the base. Tighten the set-screw at the tip, leaving just a small amount for later adjustment. Leave 3 or 4 inches on the base side, to ensure you have enough to connect it to your wrist linkage.

10. Test the action! (6:04)

At this point, you can snap the socket and tip on, and should have a fully articulating finger! Make sure it all works well before moving any further.

11. Install the bumper. (6:09)

If you use NinjaFlex or FilaFlex (more stretchy) you can probably stretch the bumper enough to get it over the tip and on to the middle section - that stuff is almost indestructible.

Lately I've preferred the cheaper Sainsmart elastic TPU, but it is not as stretchy. I print it with the cut in the bumper, which you can separate carefully with an exacto. Then wrap the bumper around, and trim the plugs as needed until it fits together well. Then I use my soldering iron (set around 3/medium) to quickly weld the TPU back together.

12. Install the linkage (7:19)

Clear the hole through the linkage, at least halfway, to make room for extra string. Make sure you've cleaned the set-screw hole and gotten one started. Feed the loose end of the tendon string into the linkage, and tighten the screw. Link the hook around a bracelet. You'll have to find the right amount to allow you to fully close the finger with the range of travel you have available.

More from Robotics

view more

All Apps

Customizer is the easiest way to take great 3D printable designs and make them your own. Make your OpenSCAD designs infinitely more valuable by empowering the community to customize them.

App Info Launch App
Customizer Thing App

This App connects Thingiverse with Makeprintable, a cloud-based mesh repair service that analyzes, validates and repairs most common mesh errors that can occur when preparing a 3D design file for p...

App Info Launch App

Kiri:Moto is an integrated cloud-based slicer and tool-path generator for 3D Printing, CAM / CNC and Laser cutting. *** 3D printing mode provides model slicing and GCode output using built-in...

App Info Launch App
KiriMoto Thing App
Comments deleted.

Nice! I am going to give it a try. I'm missing my left index finger. I really like your design.

Hi there

I was just wondering if this would work for 3 fingers and a thumb? I have partial finger amputations on one hand due to septic shock. Thanks!

Comments deleted.

Hi there

I was just wondering if this would work for 3 fingers and s thumb? I have partial finger amputations on one hand due to septic shock. Thanks!

Made one as a surprise for a friend who I thought had lost both joints on his index finger. They loved it but 'pointed out' that they'd lost only the upper joint! Has anyone worked on a 'shorter' version of this wonderful device? If not, I'll have a go and if successful post on the forum.

This design does do single joints (made one myself, see "Made" tab).

Hi, im new here, and saw this. I have had digital amputations to my right hand after necrosis. Would like to know more about your design. How can i contact you?

Could you post files to edit this in SolidWorks? I am having a hard time importing stl's and editing them. Thanks!

Dec 9, 2016 - Modified Dec 9, 2016
swoozle - in reply to Brittnee024

It's an OpenScad design, not SolidWorks. Load the file in OpenScad and see if any of the export file types helps you out.

Do you have CAD models for these other than STL? I am trying to bring it into solidworks and there is no way to get from an STL back to a solid model. Thanks

Dec 9, 2016 - Modified Dec 9, 2016
swoozle - in reply to Acal51

It's an OpenScad design. Load the file in OpenScad and see if any of the export file types helps you out.

This looks excellent. I'm going to print this as a surprise for a friend of mine who lost half his finger at work a couple of years back. Obviously if its a surprise I'll have to estimate the sizes, but I can always re-make it. I think he'll really appreciate this!

Super cool! We'd love to hear how it goes, and love to get pictures - either here on thingiverse, or we also have a facebook page too: http://www.facebook.com/dangercreations

i can't export as stl file.
error message :
Can't open file "C:/Users/���Ѿ�/Desktop/filename.stl" for export STL export finished.
are you solved this problem?

i solve this problem!
anyway, thank you~

Great, glad it's working!

Do do you change the measurements for a middle finger?

Yes, the measurements should be customized for every person's situation. There is a measurement guide that gives step-by-step on how to take the measurements, which get directly plugged into the customizer tool to generate for the individual's need.

Where is the guide

It should be in the downloads, but I keep the most up-to-date version on my site too:


hello. is this suitable for the thumb?

Hi - yes, you can configure for a single knuckle, in the event of missing one segment of the thumb.

There may need to be some customization to the linkage because of the way a thumb moves - it rotates much more than a finger, so the current linkage design might get in the way.

Can this design work for someone who is missing 3 fingers, or does this cause too much interference along the back of the hand?


Scott Collins
Instructor, Computer-Aided Design Programs
Ventura Adult and Continuing Education
Career Technical Education
Ventura Unified School District
5200 Valentine Road, Ventura, CA 93003
805.289.1744, Ext. 1205
[email protected]

Hi Scott. I've got some requests in my queue for that situation. I expect it to work just fine. It will probably require a new wrist linkage, which connects to bracelet in one spot and branches out with links to each hand, but that won't be too difficult.

Thanks for the reply, Nick. I'll see what I can come up with.

Great! I'll be happy to help or work with you, and incorporate it into the design so it can be easily configured by others in the future.

Can you tell me how to join Finger base and finger socket??


Hi there - if the socket is printed from elastic material like Ninjaflex or TPU, it should be fairly easy to join. If you wanted to do it all in PLA, then you could just combine the parts and slice them together to print as one part - but it's not comfortable to wear.

If you still have problems, make sure you've carefully removed any support material. There are also a couple settings for socket clearance that would help if you increase them, but too much will make it sloppy. Hope this helps!

this is so cool your awesome


Hi there - I'm interested in hearing from people who have printed these fingers for themselves. I am hoping to do some research into the use of 3D printed partial hand or finger prostheses. Would anyone like to share their experiences?
Thanks a lot!

Could you possibly give me some insight as to what I need to change on my Ultimaker 2+ to print the flexible parts using ninjaflex? I have 3mm sapphire Ninjaflex, and at current settings, the base does not fit the socket. What do I need to change? What settings do you recommend?

Jun 15, 2016 - Modified Jun 15, 2016
knick - in reply to johnitoalvarado

Hi - Sounds like you're getting the part to print, which is usually where people have problems with NinjaFlex - from binding in the feed gear and such. In which way does it not fit the socket?

It is a snug fit, and the support material needs to be pulled out of the inside of the socket ridge/interface point, should come out easy with needle nose pliers. Depending on how well it printed, you may want to clean up any extra material to make sure there's room for the ridge on the base to seat in the socket.

I print mine with little clearance, and firmly have to press the sides of the socket against the base to get it seated. You can also try raising the socket clearance, under advanced settings.

Hope this helps!

Update: The socket width settings which were not appearing, should now be fixed!

It says it can work w/ 1 knuckle instead of 2 ... so what parts to take away then ... it looks like you have to have the middle part regardless? Is there an STL file for just 1 knuckle to fingertip to fingersocket then?

There's an option in the customizer near the top that lets you choose the number of knuckles. In "1 knuckle mode" there is a segment that is a merge of the tip and middle section.

oh sorry i now see the customerize button lol!

Hi! I went to the customize page and just changed the finger tip cover and tip knuckle to "1 knuckle" and then "create thing". However, I've done it several times and it comes out as an error. What am I missing and are you getting the same thing? If you do happen to have the STL of both can you just e-mail it or put it the files on your thingiverse too? I'm not sure what I'm doing wrong on that customize thing.

knick - in reply to chem20

I just updated, and tried again - still working for me. I'd be happy to send you the STL, but it will depend on your settings. Send them all to me, and I can generate it. Or, it's really easy to get OpenSCAD (free) and open the .scad file in it. Then change the values in the text editor yourself, and choose "render" (takes several minutes), then "export STL". Repeat for each "part".

In the customizer, choose Part: "Tip Knuckle". Then, after it appears, change from 2 to 1 knuckle, and you should see the new modified tip piece. This will work directly with the base, no need for a "middle" part.

knick - I just tried it again and pressed "create thing". It took 15 minutes and still came out as "error". Try it yourself as well.

chem20 - I found this issue finally! It wasn't always doing it for me, but I finally reproduced it and fixed for good.

Great news! I've printed a 1 knuckle for my friend, looks good so far!

Are you talking about on the SCAD file because I don't have the program. Is there an STL file you can put it for me? I have a person who just needs 1 knuckle! Thanks.

In the same boat as ezcorer - need to increase the width of the socket, but can't see where to modify the width in the customizer app.

Hi - see the reply I just put for him!

I must just be missing it but how do i get the socket bigger? i have been looking at all of the settings but im lost.
i need the top to be 20mm and the base to be 26mm and 35mm long.

Ok - should be fixed. There were some comments in the code that previously were ok, but it appears a customizer change didn't like them. All the settings should be working now!

I must just be missing it but how do i get the socket bigger? i have been looking at all of the settings but im lost.
i need the top to be 20mm and the base to be 26mm and 35mm long.

I see what you mean. I have no idea why those settings aren't showing up - I see them in the scad file:

/ [Socket Fitting] /

//diameter of the top of socket, roughly the diameter/width of the finger stump nearer the top
socket_width_top = 17.75;
//diameter of the bottom of socket, roughly the diameter/width of the finger stump bottom
socket_width_bottom = 19.25;
//Depth of the socket, roughly equates to the length of the stump
socket_depth = 27.25;

I'm currently traveling in India, and cannot fix from here - but will mess with this in a about a week and get it figured out. In the meantime, here's a workaround:

  • Install OpenSCAD
  • download my scad file and open it
  • directly change the values in the file
  • select the right "part" to print, in this case the socket.
  • choose render, this will take ~5 minutes
  • Export as STL

Hope that helps!

Apr 6, 2016 - Modified Apr 6, 2016

can I print this in all pla? or do i need ninjaflex (ninjaflex is a pain to print)
could you also design printable knuckle pins? and could i use regular fishing line?

For the other two questions - I've found that any thinner fishing line tends to dig/cut into the PLA and stick, same goes for mono-filiment. This particular kind has been far better.

If you wanted to use plastic pins, the way to go is to just reduce the diameter of the hinge pin hole (under advanced clearances IIRC) to about 1.9 mm to allow you to directly use a section of 1.75mm PLA or ABS filament. You could do it as-is, but the hinge will be a bit sloppy. I found that metal slides way way better - so if this is for real use, I highly recommend at least using the aluminum wire, if not steel pins - which I've recently switched over to.

Not currently, the tip and the socket are pressure fit, and so require something flexible. Regardless - I can tell you from experience that the flexible socket is the only way to go for any measure of comfort - my very first wearable design was a PLA socket and it's the very first thing I changed.

Lately I've been using SainSmart Flexible TPU, which I found on Amazon. It's cheaper than NinjaFlex (about same as PLA) and is also much firmer. As long as I print slowly I can print from my Flashforge/maker clone, or even my little PrintrBot simple, with no modifications. I use 20mm/s on the big printer, or 10mm/s for PrinterBot - which is more prone to kinking.

Comments deleted.
Apr 4, 2016 - Modified Apr 4, 2016

Is there someone that might be able to make a couple of these for me? I lost my pinky and ring finger but I don't own a 3D printer. I would be willing to pay for these as my insurance is giving me the run around about prosthetic fingers.



Hi Rob,

We can probably work something out! I have started to build them for folks that aren't equipped to do themselves. Hit me up at knicksfingers {at} gmail {dot} com, where I track my queue. I'm working up some standard instructions for taking measurements. I have a short waiting list, but working through it.

muy bueno gracias!.

Wonderfull work, it will be my masterpiece!!

: )

Feb 19, 2016 - Modified Feb 19, 2016

Trying to customize this for someone but I just can't get it looking right. He's a larger guy and according to his measurements he's got 1 7/16" long nub and 28mm wide, his other finger on his other hand is 3" long and 19mm at the tip. Now, that width might still be due to swelling as he lost the finger about a month ago but putting in those measurements the base always looks huge compared to the rest. I don't have as large a hands but I tried putting in my own measurements, 2 9/16" overall, 20mm width at the knuckle and about 18mm at the tip and while it looks okay it doesn't look as good as the model's hands in the picture. What am I doing wrong or what do I need to change? Should I just scale it up on the printer after I customize it here?

Feb 19, 2016 - Modified Feb 19, 2016
knick - in reply to BliNDF123

You definitely want the model to match exactly what you need, any resizing after is not parametric and it might not interface well.

The measurements you describe seem fairly reasonable.

The hands/examples shown, and default values, are all from me. My other index finger is 74mm long, so just shy of 3 inches. When measured with a caliper, my nub is about 16mm (without compressing skin too much).

You'd want to make sure the lengths here (base, mid, tip) add roughly to the amount he's missing.

If you post the specific values you're entering, that would let me reproduce what you're doing and I might be able to tell what is wrong.

Another overall suggestion; focus on the socket. Get that printed so it fits firmly (it should be snug at first, a little lotion helps). Get that so it fits well, since it is the interface point, and then worry about sizing the finger portion.

As you say, only 1 month later he'll still be very swollen, so that's part of it. I think my first one was 24mm wide, vs 16 now. You'll want to be prepared to occasionally make smaller sockets :)

For his I was putting finger size settings: Tip length = 25mm, Middle Section = 26.75, and socket settings: Socket Width Top = 26, Socket Width Bottom = 27. Would the base knuckle and the finger socket be the ones changing as the swelling goes down or just the socket? Also seems to be a problem with the plugs, I tried importing a version I was trying earlier and they were tiny in Simplify3D. Thanks for the help!

I'll take a look tomorrow to see how these settings seem.

I thought the previews generated for the plugs looked a little off too, I'll check it out.

The base knuckle wouldn't have to change- only the socket.

knick - in reply to knick

I think you're measurements are fine. In looking at the first finger I actually wore, about a month after accident, it was a similar ratio - with an oversized socket.

What will likely help is increasing the finger width, to better match his own digit thickness, and to match better with the socket. There are some advanced settings for this, but they aren't perfect yet - I'd focused much more on the length settings initially. Currently, adjusting middle-width or middle-diameter more than a small amount results in problems with the way the hinges come together. I'll do a little work and see if I can make it easier to adjust the width in a parametric way. I'll also take a look at the plugs. Hopefully can have an update this weekend.

knick - in reply to knick

Ok, uploaded a new one, sorry about the wait. This fixes the plugs, first of all. It also should let you configure the middle_diameter and middle_width up slightly as needed to make the finger thicker, just don't go too far. I like to print a base + mid + tip once I configure new settings, and make sure those 3 parts fit together well before moving on to printing the rest of the parts.

Awesome work! Can you upload the file for the hook?

Thanks! Oops, missed that one. Should be there now.

No, Thank YOU! Great Job with this!

Thats really neat