Mini-lathe - manual drive

 It's useful sometimes to be able to manually turn the lathe chuck, particularly on these little lathes which don't have a lot of low speed torque, for example when thread cutting. Usually I just haul the chuck around by hand, using the chuck key or a bit of bar like this:

It works, but it's a bit ugly and the chuck guard gets in the way.

There are a few designs around for cranks that can be used with an expanding arbour, or the crank can be expanded into a full wheel for better control.

I made this expanding mandrel years ago as part of a dividing setup for the lathe. I used it to make a number of splined shafts and the graduated collars for the tailstock and the saddle hand wheel.

The mandrel features a journal at one end to carry a gear which provides the dividing index. An M6 threaded rod passes through the mandrel which connects with the expanding plug at the inner end.

With this mandrel already in the tool box, it makes little sense to repeat the exercise for a crank with an expanding arbour so we'll adapt the one we've got. I've made this boss for the hand wheel - it registers with the expanding mandrel on the journal where the indexing gear normally fits, but I have added a pinhole to that mandrel to enable the boss to drive the mandrel. The boss is provided with a drive pin at one end and a 1/2" BSP thread at the other, to which I fitted a pipe flange to carry the wooden wheel itself.

Here's the wheel - it's simply cut from a scrap of 3/4" plywood. The M6 threaded rod that expands the mandrel passes through the hand wheel boss into a recess on the other side such that the same threaded rod can be used both for the hand wheel and the dividing set.

The nut in the first picture is replaced with this special threaded widget which reaches down inside the boss to mate with the threaded rod and lift the expanding plug, specially designed so that the dividing setup and the handwheel setup can use the same expanding plug and threaded rod.

Here's the manual hand wheel in place with the special nut holding the expanding plug wedged into the mandrel and providing a rigid drive for the chuck.

Here's the other side. It does of course fit with the gear train cover in place.