Squeeze Wrench Part I

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I own a 3D printer and was amazed by the 3D printable NASA ratcheting wrench (picture above). The entire assembly of the wrench that NASA created could be 3D printed all at once, ratcheting mechanism and all. The main feature of this 3D printable NASA wrench was the fact that it also had full ratcheting capabilities. I was inspired by this, but wanted to make a wrench that could ratchet in both directions. Below you can see my design for a 3D printable ratcheting wrench that I designed using Autodesk Fusion 360.

Isometric View: Squeeze Wrench Assembly

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By squeezing the handle of this wrench, the standard 3/8″ size socket is prevented from spinning either clockwise or counterclockwise. By relaxing your hand, the wrench can freely spin. Below you can see that there are teeth, as well as a separation built into the main housing to allow this functionality.

Note: standard socket head dimensions were determined using engineersedge.com as a resource. Below is a link to these dimensions.

–> Standard Square Drives for Socket Tools

Isometric View: Gear and Tooth Break

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For the wrench to work, it had to be able to be printed all at once while being able to spin freely. The wrench also had to be designed with 3D printing in mind. This meant that I had to worry about things such as clearance and overhangs.

To ensure 3D print-ability, the base of the gear and the squeeze housing get printed on the print bed simultaneously. Before the wider gear portion prints, a small chamfered ring is printed underneath. This chamfer feature is intended to counter overhang deflection from the 3D printing process.

Section View: Squeeze Wrench Assembly

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Calculations

A simulation was performed by applying a load to one handle, and fixing the opposite handle. Because the deflection of the wrench is designed to be relatively large, a parabolic mesh was created. The Initial FEA that was performed resulted in a minimum factor of safety of 0.72.

FEA Analysis

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By squeezing the handle, the stress at the fillet circled in red below exceeded the yield strength of the ABS plastic. The yield strength of ABS is 20 MPA.

FEA Analysis: .025in Fillet

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A re-design was necessary in order to prevent part failure. To prevent failure, the factor of safety needed to be increased. Since the minimum factor of safety was located at the filet, I decided to experiment by increasing the fillet size. Below you can see that I decide to increase the fillet size by simply cutting a circular feature in its place.

Design Optimization

Back View: .15in Circular Feature

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By adding this feature, the minimum factor of safety went up to 1.82. Now the part could bend without failure!

FEA Analysis: .15in hole

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I was curious to see if I could increase the factor of safety by increasing the hole diameter. By doing this, I actually found that the factor of safety went down to 1.47.

FEA Analysis: .25in diameter hole

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At this point I decided that I would try something in between .15 and .25 inches. Since .25 was a pretty large jump in hole diameter, I determined that it would be best to go in between .15 and .25 inches. I chose a final hole diameter of .20 inches. By doing this, the minimum factor of safety went up to 2.27.

FEA Analysis 4: .2in diameter hole

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Squeeze Wrench Part II

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