Introduction
This antique 1935 Singer machine is missing the adjustable thread guide.
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You will need a lathe to machine appropriately sized elements to replace the mechanism.
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I used alumunium for the machined elements. Use high speed to obtain smooth surface as you need the thread to slide correctly.
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The assembly may be done used an M5 screw and a cone spring as shown.
 
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                            Conclusion
                          
                          To reassemble your device, follow these instructions in reverse order.