Printing and Assembly of Kwawu Arm

Printing and Assembly of Kwawu Arm Jacquin Buchanan December 2016 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visithttp://creativecommons.org/ licenses/by-nc-sa/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA. Printing and Assembly of Kwawu Arm Page 1

Choosing Files to Print The STL files necessary to create the forearm portion of the prosthetic come in three different versions. This was done only to make printing on smaller printers possible. If you have a very large printer bed, then you can print the forearm as one piece. If your printer bed cannot fit the whole forearm (STL file Arm (1of 1) ), then you will need to use the forearm broken up into 2 pieces or or six pieces, then glue the pieces together with CA glue or super glue. The files Form (1 of 3).stl, Form (2 of 3).stl, Form (3 of 3).stl are not part of the arm itself. These are used to create a form to help shape the forearm. If you have a cast of the recipients residual arm that may work better than this form. Files to print based on printer size and a 100% scale arm filename 5 x5 printer bed 8 x8 printer bed 12 x12 printer bed Arm (1 of 1).stl 1 Arm (1 of 2).stl 1 Arm (1 of 6).stl 1 Arm (2 of 2).stl 1 Arm (2 of 6).stl 1 Arm (3 of 6).stl 1 Arm (4 of 6).stl 1 Arm (5 of 6).stl 1 Arm (6 of 6).stl 1 CAM1.stl 1 1 1 CAM2.stl 1 1 1 Cuff.stl 1 1 1 Elbow Bolt (x2).stl 2 2 2 Finger Knuckle Hinge (x4).stl 4 4 4 Form (1 of 3).stl 1 1 1 Form (2 of 3).stl 1 1 1 Form (3 of 3).stl 1 1 1 LeftPalm.stl 1 1 1 LH_Finger_Plate.stl 1 1 1 Printing and Assembly of Kwawu Arm Page 2

filename 5 x5 printer bed 8 x8 printer bed 12 x12 printer bed Phalanx Hinge (x9).stl 9 9 9 Tensioner (x2).stl 2 2 2 Thumb Hinge.stl 1 1 1 WhippleTree.stl 1 1 1 Wrist Bolt (x2).stl 2 2 2 Resizing the Arm The 100% arm size was made to fit an adult male. All the pieces can be scaled up or down by at least 40%. This should make it possible to fit most adults. Simple scaling is not likely to work in order to make this design fit a child. A different set of files would be necessary. When sizing for an adult, scaling the forearm, hand, and cuff separately should be possible up to a 20% difference. You may need to drill out the wrist holes in the forearm if you scaled the forearm piece lower than the hand or cuff. It is best to scale everything within these three groups at the same rate, though you may be able to scale the groups separately by as much as 20% and still fit pieces together: Hand group LeftPalm.stl, Finger Knuckle Hinge (x4).stl, LH_Finger_Plate.stl, Phalanx Hinge (x9).stl, Thumb Hinge.stl, WhippleTree.stl, Wrist Bolt (x2).stl Forearm group Arm (1 of 1).stl, or Arm (1 of 2).stl, Arm (2 of 2).stl, or Arm (1 of 6).stl, Arm (2 of 6).stl, Arm (3 of 6).stl, Arm (4 of 6).stl, Arm (5 of 6).stl, Arm (6 of 6).stl, CAM1.stl, CAM2.stl, Form (1 of 3).stl, Form (2 of 3).stl, Form (3 of 3).stl Cuff group Cuff.stl, Elbow Bolt (x2).stl, Tensioner (x2).stl Print Settings and Suggestions Printing and Assembly of Kwawu Arm Page 3

Most parts can be printed in PLA, except the hinges which must be printed in a flexible material like TPE or TPU. Some of the rigid parts can be printed in other materials like ABS, experiment if you like. Rigid Hand Parts LeftPalm.stl, LH_Finger_Plate.stl 3 or 4 outer layers, that includes top, bottom layers and outer perimeters. 35% honeycomb infill. Can be material other than PLA, such as ABS. 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. Thermoformed Parts Arm (1 of 1).stl, or Arm (1 of 2).stl, Arm (2 of 2).stl, orarm (1 of 6).stl, Arm (2 of 6).stl, Arm (3 of 6).stl, Arm (4 of 6).stl, Arm (5 of 6).stl, Arm (6 of 6).stl, Cuff.stl 3 or 4 outer layers, that includes top, bottom layers and outer perimeters. 35% honeycomb infill. Must be PLA, since these parts will be thermoformed. The cuff requires scaffolding to print. Most slicers will automatically generate scaffold that will work. Structural Parts Wrist Bolt (x2).stl, CAM1.stl, CAM2.stl, Elbow Bolt (x2).stl, Tensioner (x2).stl, WhippleTree.stl 4 or 5 outer layers, that includes top, bottom layers and outer perimeters. near 100% infill for strength. Can be material other than PLA, such as ABS. Thermoform Form Form (1 of 3).stl, Form (2 of 3).stl, Form (3 of 3).stl 3 or 4 outer layers, that includes top, bottom layers and outer perimeters. Printing and Assembly of Kwawu Arm Page 4

35% honeycomb infill. If you are using non-pla you can use a lower infill to save plastic. Can be material other than PLA, such as ABS. It can be a benefit to use ABS for this part so you can place the hot forearm over this form without the form itself changing. I have always printed this form in PLA and not had a problem with it getting too hot from the forearm wrapping on it. Flexible Parts Finger Knuckle Hinge (x4).stl, Phalanx Hinge (x9).stl, Thumb Hinge.stl 4 or 5 outer layers, that includes top, bottom layers and outer perimeters. near100% infill for strength. Must be a flexible material such as TPE or TPU. Brand names for TPE are NinjaFlex and FilaFlex. I have only tested these two brand names. 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. Printing and Assembly of Kwawu Arm Page 5

Non-Printed Parts 2 x Pan Head Phillips Sheet Metal Screws These are used to hold and adjust the string tensioner. For an arm scaled at 100% use; US #8 by 1.2 inches. 80-100 lbs Strength braided Fishing Line Spectra is a brand name for this fishing line. For a 100% size hand you will need about 10 feet. 3/8 Thick Self-Adhesive Firm Foam This lines the inside of the Forearm and the Cuff. Medical grade foam is better. Inexpensive foam can grow mold, and deteriorate over extended use. 8 x Velcro straps, 12 long, 1 wide, non-elastic (often sold as cable straps) You may prefer 4 x 12 long 2 wide straps of the same type. 5 x Lee Tippi gel Finger Tips Not required, but these really allow for better gripping of small items. Printing and Assembly of Kwawu Arm Page 6

Tools for Assembly Required Tools We tried to keep the required tools list as short as possible. Thick CA glue such as Superglue for assembling the forearm and sealing the knots in the fishing line. Phillips head screwdriver to fit the Pan Head Sheet Metal Screws. Flat head screwdriver or similar item to push the flexible hinges in place. Sharpe knife or scissors to cut the fishing line. Pot of hot water for thermoforming. Printing and Assembly of Kwawu Arm Page 7

Recommended tools Small flat file, Small round file, Medium half round file; to clean printed parts. toothpick or similar disposable fine tip to help spread the glue. utility knife or razor to help clean parts. A sharp razor is helpful to clean stringing off the flexible parts. A pair of niddle nose pliers can come in handy. A heat gun is very useful for thermoforming. And some leather gloves to handle the hot plastic. Printing and Assembly of Kwawu Arm Page 8

Assembling the Hand Arrange the finger pieces in order that they will fit on the hand. Each of the finger parts is different so you will want to be sure you have thee right pieces in the correct order before you begin assembling the hand. Note: That the finger parts are arranged in the LH_Finger_Plate.STL file in the same way they will go on the hand. Printing and Assembly of Kwawu Arm Page 9

Start by putting in the knuckle hinges. The solid tube of the hinge slides on the finger portion. Note: All the hinges are bent to hold the fingers open. So the bend should always go towards the back of the hand. Sliding the hinges in place should be tight but not impossible. You may need to file out the opening. Push the Open tube side of the hinge into the palm with a flathead screwdriver or similar tool. this can take some force if you printed with NinjaFlex, which is a little stiffer than FilaFlex. Assemble the remainder of the finger pieces. Note that even the phalanx hinges are bent towards the back of the hand. Printing and Assembly of Kwawu Arm Page 10

Assembling the Forearm If you are lucky enough to have a big printer and printed the whole forearm in one piece you can skip this section. Use thick CA glue such as Superglue to adhere the forearm pieces together. Use the toothpick to spread a small amount of glue along the connecting edges of the arm pieces. NOTE: Connect the pieces horizontally first then vertically, as shown. NOTE: At this point before thermoforming you can trace and cut the foam to fit inside the Forearm and cuff. Do NOT adhere the foam until after thermoforming. Printing and Assembly of Kwawu Arm Page 11

Thermoforming the Arm and Cuff The files Form (1 of 3).stl, Form (2 of 3).stl, Form (3 of 3).stl are not part of the arm itself. These are used to create a form to help shape the forearm. Even if you have a cast of the recipients residual arm it is recommended to use this form first in order to get a good twist in the arm, and to get the wrist end to fit in the hand easily. Then use the recipients cast to adjust the forearm. Glue the three pieces of the form together. The Form has threaded holes where attachments will be. You can print four extra Wrist Bolts and screw these into the form to help guide the forming process. These bolts are removable so you can take them out and more easily remove the formed forearm off the mold. There is no form for the cuff. Just make sure when you form the cuff you use the end of the forearm to make sure the bolt holes line up. NOTE: This document will not review how to thermoform, there are many videos online. Basically you heat the plastic until it is soft, in hot water is typical, form it, and wait of the plastic to cool in its new shape. Repeat until desired shape is created. Printing and Assembly of Kwawu Arm Page 12

Wiring the Hand Thumb String 1. Cut a long piece of the Spectra string, long enough to reach from the tip of the thumb to the tensioner in the cuff (give yourself extra). 2. Tie one end to the end of the thumb. 3. Feed the long end of the string through the thumb phalanx holes. 4. Feed the string through the pipe in the palm, then through the hole in the base of the palm. Back of whippletree String 1. Cut a long piece of the Spectra string, long enough to reach from the palm to the tensioner in the cuff (give yourself extra). 2. Tie on end to the backside of the whippletree. 3. Feed the long end of the string backwards through the hole at the base of the palm. 4. Leave the whippletree out of the palm for now. 5. Go ahead and put glue on this knot now. Soon it will be in the palm and you cannot get to it again. Index and Middle Finger String 1. Cut a piece of Spectra string long enough to reach the tip of the index finger past the wrist and back to the tip of the middle finger. (give yourself extra) 2. Tie one end to the tip of the index finger. 3. Feed the rest of the string through all the holes down the finger phalanx. 4. Feed the string through the whole in the palm under the knuckle. 5. Feed the string out the base of the palm and around one loop in the whippletree. 6. Feed the line back through the palm and up the middle finger in the same fashion. 7. Do not tie off the string at the end of the middle finger yet. Ring and Pinky Finger String Printing and Assembly of Kwawu Arm Page 13

1. Cut a piece of Spectra string long enough to reach the tip of the ring finger past the wrist and back to the tip of the pinky finger. (give yourself extra) 2. Tie one end to the tip of the ring finger. 3. Feed the rest of the string through all the holes down the finger phalanx. 4. Feed the string through the hole in the palm under the knuckle. 5. Feed the string out the base of the palm and around the other loop in the whippletree. 6. Feed the line back through the palm and up the pinky finger in the same fashion. 7. Do not tie off the string at the end of the pinky finger yet. Tension the Finger Strings 1. Pull the remaining strings in the middle finger and pinky finger, and draw the whippletree into the palm. 2. Pull these strings until the whippletree is touching the inner wall of the palm. 3. Tie the strings to the end of the middle finger and pinky finger respectively. NOTE: You want to pull the finger strings as tight as you can without bending the fingers inwards. So there is no slack in the string, and the whippletree is tight up against the inside wall of the palm. Printing and Assembly of Kwawu Arm Page 14

Attaching Arm Hand and Cuff Insert the wrist end of the forearm into the slot around the base of the palm. Use the two wrist bolts to secure in place. Use the Elbow bolts to fasten the cuff and cams to the forearm. Final Wiring and Tensioning Feed the two strings from the hand through the first channel on the back of the forearm. Continue to feed one string straight up the side of the forearm through the other two straight channels. Feed the second string through the other channels leading across the forearm to the other side of the elbow. Move the cams so they are in the most upright position, i.e. out of the way of the string. Loop the string thought the hole in the tensioner, but don t tighten the string yet. Position the tensioner in its slot so the hole goes side to side, not up and down. This better positions the string to stay in the slot on the cam. Use the pan head sheet metal screw to attach the tensioners to the cuff. Only turn the screws till they catch the tensioner in place, do not tighten them yet. Printing and Assembly of Kwawu Arm Page 15

Make sure the fingers are fully open and the elbow is fully extended. Pull the strings tight and tie the knots to the respective tensioner. The arm should be fully functional now. Change the cams in different positions to change the grip. The cam position is changed by lifting the cam outward slightly then rotating it to a new slot and pushing it back down. The thumb is on one side of the elbow and the fingers are on the other side. By adjusting the closure rate of the thumb and fingers separately, the wearer can achieve various grip types. Trim any leftover string and put super glue on all the knots. Let the glue dry. Velcro Straps 1. Feed a Velcro strap through a slot on the thumb side of the forearm from the outside with the fuzzy side upwards. 2. Feed the strap through the buckle in the velcro. 3. Feed the strap back through the forearm slot. 4. Twist the buckle upwards and feed the strap through the forearm slot but not the buckle this time. 5. Pull the strap tight then attach a second strap using the same technique to the other slot on the same side of the gauntlet Use the same technique to attach velcro to the other slots including the cuff. Finger Tips Lee Tippi gel fingertips can be stretched over each finger and thumb tip to provide a soft and tacky surface for an improved grip. Printing and Assembly of Kwawu Arm Page 16

NOTE: Don t fit the Lee Tippi gel fingertips until the CA glue on the knots is thoroughly set as wet CA will melt the gel material. Padding and Fitting The padding was cut to fit the forearm and cuff when they were flat, before thermoforming. After thermoforming, peel the back off the padding and stick it to the inside of the forearm and cuff. You may want to save inserting the padding as part of fitting for the recipient. With the recipient present you may want to adjust the fit of the arm by thermoforming it some more. usually the heat required to thermoform the arm will not damage the foam, but it may be easier to adjust without the foam. Fitting the arm and training should be done by someone with medical experience with prosthetics. Printing and Assembly of Kwawu Arm Page 17