Those of you who own Myford series 7 lathes will know that when confronted by odd screw threads a full range of change gears is the order of the day. However, some of the original series of change gears are no longer available, in particular, the 46-tooth change gear is no longer to be found. Without this particular gear one cannot cut either a 46 tpi or a 92 tpi screw thread.

Now let me be honest. I’m not really sure that I will ever need to cut either of these threads. But I somehow suspect that Murphy’s Law dictates that given enough time someone will ask me to cut one these threads for some odd bolt, shaft or stud that is needed for repair work.

Instead of burning up a lot of machining time to create this gear I chose for the cheap route and decided to try 3D-printing one of these gears in PLA plastic filament. I’m not the first to do this. There are various videos on Youtube of others who have done the same.

I opted to use the freeware program FreeCAD that has a built-in gear generator algorithm. The form I generated was passed into the Blender 3D software for inspection and cleanup and from there I wrote out a file in the .stl format which I sent to a friend of mine who has access to a 3D-printer. One day later he presented me with two copies of the gear.

The photos pretty much tell the rest of the story. The gear slid into place without any undo fettling. It meshed perfectly with the other metal gears in the train and (most important of all) didn’t fly to pieces when under power.

A test cut was made at 46 threads per inch. However, my thread gauge set can measure either 40 tpi or 48 tpi, but hasn’t provision for that elusive 46. So just to be sure, I held the points of a vernier caliper against the shaft and using a magnifier counted the threads for a measured distance along my work. Success!

So, now these plastic change gears will go into the drawer, there if I need them in the future.

Hope this inspires some of you.

The gear file is now posted on Thingiverse.

Just follow this link: Myford 46-tooth gear at Thingiverse

Edited By Ignatz on 24/07/2022 21:59:36