View Full Version : Threading issue..."nut" fits fine in one direction, but binds when turned around.

10-26-2012, 01:21 PM
I turned a male thread to match the threaded spindle on my JET 1024 lathe. It fits fine in the chuck, faceplate, and spare backplate.

Then I turned a female thread to make a spindle nose protector using the male thread to check the fit. The protector fits just right on the spindle threads. When I was turning the internal threads, I was running the bit completely through the piece, so the threads would be the same all the way through.

Now the rub: The male thread I turned first is a perfect fit all the way through the thread protector in one direction. However, when I turn the thread protector around, it binds after several turns. It's the same if I start from the other end, too.

What defect in the threads (or in the threading procedure) could cause that?

10-26-2012, 01:33 PM
One of my first thoughts would be thread flank angle.
Imagen two buttress threads, they go togethor fine one way, but not when one is turned around. (I don't think you got your threads THAT wrong, but if you are like me, you left ohh, 1~3mils or so clearance, so the slightest mistake will cause it to bind)

I had a similar problem where I made the thread pitch PERFECT, OD PERFECT... Except because the crests of my thread where square and not rounded (like the aluminum test plug I made was after the first 'slightly binding' insert), the steel bound badly in the lathe spindle threads untill the spindle threads basicly formed round crests! If I had kept reducing the pitch diamiter it would of been a long time before I got those crests skinny enough.

10-26-2012, 03:23 PM
Yeah, that makes sense. It would be really easy to get one or both tools off just a little when grinding by hand and eyeballing the setups on the lathe.

Maybe I can use them for a puzzle, similar to the one-way screw thingie. :D