Singer 760G cam stack drive gear

thingiverse

The "Touch and Sew" series of sewing machines are nearing the end of their lifespan. The cam stack drive gear is breaking on most 760Gs, forcing owners to bin them due to an unavailability of a replacement part. It's unfortunate they no longer manufacture such quality products. Replace it with this readily available gear. There are two versions of the drive gear: * Early production models feature a metal worm gear attached to the main arm shaft via two grub screws. The cam gear measures approximately 30mm in diameter. * Later G3 models have a worm gear integrated into the arm shaft, and the cam gear boasts a larger diameter with a steeper helix angle. This project focuses on the smaller gear suitable for earlier models. The larger G3 gear can still be purchased from various vendors. **This fix is intended for experienced repair professionals.** The cam stack, comprising its gear, was assembled in the factory by gluing and pressing together two parts to form a single piece. Assuming the cams remain functional, the gear will need to be carefully cut off and a new gear glued back on. Before cutting off the gear, accurately measure the distance between the top of the metal shaft and the top of the cam stack; it should be approximately 4mm (see photo 3). The stack may shift during gear removal, and there is no way to lower the cam stack or raise the cam followers in the 760. Position the cam stack perfectly. Cut the gear off as cleanly as possible without damaging the metal shaft (I used a small hobby lathe). Sand the bottom of the cam stack flat and square. Consider how you will join the gear to the stack; it must be glued, but some interlocking is beneficial. I cut three slots in the cam stack to receive pegs from the gear, ensuring rotational force transfer isn't solely reliant on glue (visible in photo 4). Next, determine the spacer height, which depends on where you cut off the gear and how you intend to join the new gear to the stack. Enter this value into the SCAD file, render the gear, and export it as an STL. When choosing a filament, consider its type. I've had success with annealed PLA but PETG might be a better choice for standard temperature printers (although PETG is harder to glue). If using annealed PLA, try the following scaler settings in your slicer: * X and Y: 101.7% * Z: 96% Set overall wall thickness to 1.2mm; this is where strength should be focused. Print the gear and continue with post-processing instructions...