Introduction

This chapter assumes you have already followed the instructions in the File Preparation chapter and if you are making a custom socket the instructions from the Socket Preparation chapter. You should have a collection of correctly sized STL files. This chapter will cover the recommended 3D printing setting and materials for all the 3D printed components. This is not a guide to 3D printing.

The majority of the documentation here was copied from the "Printing and Assembly of Kwawu Arm 2.0 Socket Version" pdf which was written by Jacquin Buchanan, the original files can be found here.

Print Settings and Suggestions

Most parts can be printed in any solid printing material such as PLA, ABS or PETG; PETG is recommended as it is the strongest and still relatively easy to print with. The hinges which must be printed in a flexible material like TPE or TPU. Some of the parts requiring thermoforming like the cuff can be printed in PLA, though I still recommend PETG. Experiment with different materials if you like. I recommend printing the palm and finger parts in PETG. PETG does not deform in hot water like PLA, it’s harder than PLA and comes in food safe versions. This makes the hand safer and easier to use for eating and able to wash in hot water. You can thermoform PETG with heat gun so I do prefer it even for the thermoform parts.

Note on Flexible Material :

You want to use a flexible material with a Shore A Hardness of about 85A. Most newer TPU is a Shore A Hardness of about 94A. They have made this newer stiffer filament because it is easier to print. The original softer style used to be called TPE, ThermoPlastic Elastomer, and the newer harder style was called TPU, Thermoplastic PolyUrethane. But really they are both in the same chemical families just mixed to different hardnesses. I generally use the brand names NinjaFlex and FilaFlex. The brand NinjaFlex is the original material from a company called NinjaTek. They have since come out with several other flexible filaments all with different properties. So be sure to get the one with Shore A Hardness of 85A. Likewise FilaFlex is a company whose original product was Shore Hardness 82A. They have since come out with FiliaFlex Medium which is Shore A Hardness 95A .

So remember get the softer filament. It is a little more difficult to print, but produces better flexible hinges.

Rigid Hand Parts

Palm top and bottom, all the finger pieces, the motor box, the socket mould, lids, spacing plates

• 3 or 4 outer layers, that includes top, bottom layers and outer perimeters.
• 35% honeycomb infill.
• Can be material other than PETG, such as ABS or PLA. I like using PETG because it is stronger and can therefore be made thinner and lighter than PLA. Also a PETG hand can be detached and washed easier than other materials.
• Printing the finger pieces can benefit from scaffolding. Generally it is better to use a slicing program that will let you manually place the scaffolding for these parts. If you are having trouble with the fingers coming loose from the base plate, try learning them back to a 45 degree angle and adding more scaffolding. This may add to the time to clean the parts, but can be more reliable for some printers.

Thermoformed Cuff Part

• 3 or 4 outer layers, that includes top, bottom layers and outer perimeters.
• 35% honeycomb infill.
• these are recommended to be PETG. If you don’t have a heat gun to thermoform then use PLA since this will be thermoformed.
• The cuff requires scaffolding to print. Most slicers will automatically generate scaffold that will work.

Structural Parts

Bolts, Whippletrees, servo horns

• 4 or 5 outer layers, that includes top, bottom layers and outer perimeters.
• near 100% infill for strength.
• these are recommended to be PETG or ABS for added strength.
• The Wrist Bolt must be pretend because it has a hole down the middle.
• You do not have to print the other bolts. All the bolts and threading are printed as standard ISO metric sizes. I recommend you print the bolts only so you can go to the hardware store and use the printed version as a quick guide for picking out the bolts at the store.

Flexible Parts

All the hinges, Pencil Holder Cover, Wrist Compression Bushing, Socket Lining

• 4 or 5 outer layers, that includes top, bottom layers and outer perimeters.
• Use enough outer layers to get near 100% fill for strength and proper spring behavior.
• Must be a flexible material such as TPE or TPU. Brand names for TPE are NinjaFlex and FilaFlex . You want to use a flexible material with a Shore A Hardness of about 85A.
• These parts are small and intended to be easier to print then most parts. But printing with TPE or TPU is NOT easy. The best advice is to print very slow, like 900mm/min; and hot, around 230 C.
• You want these parts to fit snug in the finger slots. Because printers behave differently for these materials than the rigid plastics you may have to print these smaller or larger. Sometimes as small as 90% or as large as 110%.

Note: When scaling the hinges make sure you scale only in the z and y direction so that the hinges get fatter but not longer

Socket

• Print with 3-4 Perimeter Layers
• Use 30% Infill
• Must use a flexible filament, this filament does not need to be as soft as the material the hinges are printed out with, we used a filament with a Shore A Hardness of approximately 95A, but this will change greatly depending on the needs of your recipient.

Recommended Printing Orientation

All the parts should be generated by OpenSCAD into the preferred orientation for printing.

Two orientations for printing finger parts. Use more scaffolding if the part comes loose from the base plate. Or make a large Brim attached to the supports.

Three orientations to print the Palm Top. The 45 degree angle was suggested by Krzysztof Grandys and is the preferred orientation of Jacquin Buchanan (creator of the original Kwawu Arm) for best look and strength.

Often different printers will prefer other orientations, so feel comfortable to experiment.