Tumble Reverse Mod

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I have added a tumble reverse function to the gearbox of the lathe, allowing power feed away from the chuck and turning of left hand threads.

I followed the drawing linked on the Yahoo 9x20 Lathe forum, uploaded by [oldplanecollector]. Note: you'll need a Yahoo account to access the files.

I started by cleaning up and metric-ing the drawing of the lever assembly, followed by modelling a spider-webbed version to be 3D printed. This was to check that it would fit, mesh and not collide with anything. As with most tumble reverse mods, I needed to countersink the bolts holding the belt tensioner plate, so they were flush with the surface.

80T and 45T Acetal gears were bought, and I fitted bearings to these, in a similar manner to the Micro Machine Shop post, except that my gears had extended hubs, and I used lower profile bearings. I turned some large bolts (M16 I believe) down to create the pins for the gears. This was all fit up on the printed lever and proved to work.

A plate of 12mm Aluminium was skimmed to thickness on the CNC, the position of the holes pilot drilled, and then the profile cut out. The holes were drilled to size, and tapped. The larger hole at the bottom was bored to suit a brass insert, on which the assembly pivots. This brass part also serves as a spacer, and needs to be carefully sized so that the pin it sits on can be fully tightened, the following gear stack assembled and the 'C' clip fitted, without causing binding. From stock, this spacing is achieved by a collar with a grub-screw.

A handle was turned to match the gear selector on the front of the lathe, with a spring loaded plunger. This screws into the top of the assembly and locates on a block mounted to the top of the spindle housing. This block was 3D printed, to ensure correct spacing of the holes; good meshing of the gears at both ends, and good clearance in the neutral position. The gearbox door had a small cutout removed to clear the lever.