Problem Lowering Milling Head, Round Column (3 In 1)

Hello, I have a 3 in 1 machine that has sort of a round column to raise and lower the milling head. It's about exactly in the center of the picture below. The column is threaded so that you can use its collar to raise the head up. The problem is I can't get the head to go down once I've raised it up. The only way I've been able to lower the head is by carefully hammering on it. Is there a better way?

View attachment 129396

You can see the pinch bolt at the lower left of the Smithy...

Problem Lowering Milling Head, Round Column (3 In 1)