atlas half nut won't stay engaged

Half nut on the Atlas drops out about halfway down a thread. Cam lever feels soft. I can hold it in with my thumb and the thread is fine, which is not a long-term plan if I like my thumb.

Soft cam is usually a worn shoe or the detent, not the half nut threads themselves. If holding it with your thumb makes a good thread, the leadscrew and the nut are still a pair. Look at the cam flat before you buy a nut.

Mine was the spring on the detent, not the cam. $2 spring, and I had already talked myself into a $90 nut. Check the spring before you become me.

It was the shoe, flat as a table. I filed a new one out of some keystock and hardened it badly, which is to say I heated it and hoped. It stays in. Thumb is retired.