#  Step 2: Mold Stiff Ends 

 



 ##  

  expand\_more  

 
  

 

   ![step2-1.png](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-1.png?itok=AcUpF07C) 

 

- The next step is to make the stiff end pieces of the sensor. To begin, inside a fume hood, spray the center-displacement piece with mold release. Make sure to spray the side with the raised ridge. Sorta-clear is very stiff, so without mold release the 2 mold pieces will be glued together
- Mix a small amount of Sorta-clear elastomer in a cup. Not much is needed, only roughly 10 grams.
- Refer to the [Bill of Materials](/book/egain-bom) section for vendor information.

SortPour stiff rubber   ![step2-2.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-2.jpg?itok=hSo3aEsM) 

 



- Insert velcro pieces into mold through the slots on the ends with the fuzzy size face down.



   ![step2-3.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-3.jpg?itok=CTchJxEF) 

 



- With a tongue depressor, apply elastomer beneath the exposed velcro. Make sure the fuzz is thoroughly coated.



   ![step2-4.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-4.jpg?itok=gBzFIfzu) 

 



- Align the velcro using the pegs, then apply elastomer to the top of the velcro as well. Excess elastomer should be left in the end circular areas of the mold.



   ![step2-5.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-5.jpg?itok=YDwZ7DKd) 

 



- The image on the left shows a mold with fully coated velcro end pieces. Note how there is some velcro sticking out of the ends of the mold.







SortDegas elastomer   ![step2-6.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__720x720_scale/public/sorotoolkit/files/step2-6.jpg?itok=FoLoXw6g) 

 



- Place the mold with velcro and elastomer into a vacuum chamber and degas (set the vacuum chamber to -90 kPa). Release and restore the vacuum several times to help pop many of the bubbles. Then leave the mold in the machine for a few more minutes until bubbles start dying down.



   ![step2-7.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__720x720_scale/public/sorotoolkit/files/step2-7.jpg?itok=MtOmxJae) 

 



- Remove the mold from vacuum chamber and inspect for bubbles, particularly ones near the interface between the velcro and elastomer, as these will turn into failure points.
- To remove any remaining bubbles, dip tweezers into the elastomer and slowly “push” the bubbles towards the edges and “lift” them out of the elastomer.







SortSeal and press mold   ![step2-8.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__720x720_scale/public/sorotoolkit/files/step2-8.jpg?itok=qgOU1NMC) 

 



- Put on the top piece of the bottom mold, raised side down. Press it down gently so the pegs align, then apply gentle finger pressure from the center moving outwards.
- This process will keep the elastomer out of the middle portion of the mold, which is where the softer elastomer will go later.



   ![step2-9.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__720x720_scale/public/sorotoolkit/files/step2-9.jpg?itok=2LLtoYOM) 

 



- Place the molds in a 60 oC oven and put weights on top.
- Remove from the oven after 15 minutes.







SortCheck for defects   ![step2-10.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-10.jpg?itok=L0flXDa6) 

 



- After taking the mold out of the oven, peel off any excess elastomer from around the edges. Pry off the top using a tool to gain leverage, such as a screwdriver.
- The pieces should be non-tacky but brittle (it will take a day to reach full strength).



   ![step2-11.jpg](/sites/g/files/omnuum4601/files/styles/hwp_1_1__360x360_scale/public/sorotoolkit/files/step2-11.jpg?itok=czkMewBO) 

 



- There should be no gaps or bubbles and the interface/edge of the stiff elastomer should be clearly defined.
- Peel excess elastomer off the pegs to make next step easier.







### Bibliography

Mengüç et al. (2013) [Soft Wearable Motion Sensing Suit for Lower Limb Biomechanics Measurements.](/publications/soft-wearable-motion-sensing-suit-lower-limb-biomechanics-measurements)

Mengüç et al. (To appear in 2014) [Wearable Soft Sensing Suit for Human Gait Measurement.](/publications/wearable-soft-sensing-suit-human-gait-measurement)

Miserez et al. (2008) [The Transition from Stiff to Compliant Materials in Squid Beaks.](/publications/transition-stiff-compliant-materials-squid-beaks)

Muth et al. (2014) [Embedded 3D Printing of Strain Sensors within Highly Stretchable Elastomers.](/publications/embedded-3d-printing-strain-sensors-within-highly-stretchable-elastomers)

Vogt, D. M., Park, Y. L., & Wood, R. J. (2013). [Design and Characterization of a Soft Multi-Axis Force Sensor Using Embedded Microfluidic Channels.](/publications/design-and-characterization-soft-multi-axis-force-sensor-using-embedded)

### Contributors

Yiğit Mengüç