Introduction

This document will walk you though using OpenSCAD to size and make printable STL files for the El Medallo. You should already have the required patient measurements from the Patient Information document. This document will not cover how to make a custom form fitting insert using Fusion 360, that is a seperate guide.

The majority of the documentation here was copied from the "Using OpenSCAD to Render Kwawu Arm 2.0 - Socket_Version" pdf which was written by Jacquin Buchanan, the original files can be found here.

Downloading Files

All the necessary files can be grabbed from our google drive, the file you want is called "OpenSCAD Files.zip". The other folders can be ignored, this is for continued development of the El Medallo prosthetic within the eNABLE community and is not needed for a regular assembly.

Downloading and Installing OpenSCAD

1. Download and install OpenSCAD. You need the latest development snapshot to be able to use the customizer feature. Unlike the old stable version which has a yellow program icon, the development snapshot has a blue icon. You can find it here: http://www.openscad.org/downloads.html#snapshots

2. Once you have installed OpenSCAD, open the file “El_Medallo_1.0_Prosthetic_Arm.scad”

3. Go to the Preferences menu, and in the ‘Features’ section, ensure Customizer is enabled (you only need to do this once).

4. Uncheck ‘Hide Customizer’ in the View menu to show the Customizer UI at the right.

5. In the Customizer menu on the Right Hand side, click the little black arrow to display the parameters. Make sure “Automatic Preview” and “Show Details” are both checked.

6. Hit the Preview button (F5) to get a quick preview (should not be necessary if ‘Automatic preview’ is enabled).

You should see a preview of the palm in the main window it looks something like this.

If the object is too large or small press the “View all” button

Now you are ready to set all the sizing parameters. Once you have set all the parameters you will need to render each part and save to an STL file.

Sizing Parameters

Enter the patient measurements as various parameters into the Customizer Parameters sidebar.

Part

Only one part can be previewed, and/or render at a time.

Left Right

Choose which arm you will be making left or right.

Arm Length, Forearm Circumference, and BicepCircumference:

All are from the direct measurements take in the previous section. While these can be any numbers allow by the sliders, you will want all four sliders to be roughly aligned vertically. If the sliders do not roughly line up vertically together then the arm will likely have an unnatural look to it. Meaning you will have a child’s hand on an adult’s arm or vice versa. The arm length should be no less than 225 for all the components to fit comfortably.

Padding Thickness

Choose the thickness of the padding that will be used to line the cuff and forearm. This thickness will contribute to the overall circumference of the forearm and the cuff.

For the El Medello we found that often me make the stump and electronics fit into the socket we had to have a proportionally large forearm circumference/increase the Padding Thickness. To compensate for this setting hand scale between 80-90% makes the hand look normal.

Additional Hand Scale

This parameter allows scaling of the hand above or below the basic scale of the arm. This is sometimes necessary if the recipient has a particularly “stocky” arm, or the opposite a thin arm with large hands. Left at 100% the arm will always make a smooth transition to the hand. If this scale is less than 100% there will be an edge at the wrist, because the wrist is larger than the hand. If this is above 100% there will be an edge because the hand is larger than the arm.

Arm Pieces

The forearm can be printed as one or two pieces. If it is printed as more than one piece you will glue the pieces together with 2-part epoxy or super glue. The only reason to use more than one piece is so it will fit on your printer bed. To get a rough idea to know if the part will fit on your printer, you can preview it specifically.

If you choose orthogonal view markings in the arm. and view from the front, you can see the measurement

If you select Arm Pieces “1” and Preview Part “Arm1”, you get a view where you can estimate this arm would require a 31 centimeter long bed to print.

Palm Bolt Diameter

Choose a threading size for the bolts holding the palm together. All threads are rendered as standard ISO metric threading, so you can use manufactured bolts rather than the printed ones.

To Choose the palm bolt size, select “Palm” as the part to preview. If the hole looks too larger adjust to a different size bolt.

Preview of Palm Bolt sizes; too large, too small, and just right.

Elbow Bolt Diameter

Choose the threading size for the bolts holding the arm to the cuff. This is best decided while viewing the cuff from the top or bottom.

Preview of Elbow Bolt sizes; too large, too small, and just right.

Pencil Holder

If chosen a cut out is made in the palm to slide a soft pencil holder.

Cuff Heighten

This makes the cuff fit much better if the bicep circumference is much smaller than the forearm circumference.

Render and Save STL files

You will have to select each part to preview then press Render, and then Save STL button.

NOTE: The render button can take a long time for some parts (20 minutes or more).

The parts contained in the folder "ready_for_print" do not need to be rendered in OpenSCAD, these files can be loaded directly into a slicer and printed, you will need 1 copy of each of these to assemble the bionic prosthetic.

Exporting Files for Fitted Insert Preparation

If you are making a custom fitted insert for the recipient render and export the Arm2Interior part, do not print this file, it is a template for the form fitting insert. The Arm2 part rendered export (or if you are printing a single arm component, the Arm part render) will also be modified in the process of making the custom insert.

If you will be creating the custom insert, move to the next chapter, if someone else is making the insert then pass them the 2 stl's as well as the scan of the recipients stump.

Have Fun!