Lump in the ground! What and where? (See below.)

Yes, you're on the right track with Nancledra but that was not its function, CW!

Pivot for stone crushing - Giew Mine?

When I say right track with Nancledra, I mean it, and I'm not talking about mines!

May I suggest that someone visit the village and ask? A visit to Helston Museum will make the second answer come to light if enquiries fail! The excellent Museum is free by the way!

A counterweight for a lifting device?

I'm afraid not, CW, but I congratulate you on being the only one recently to attempt to solve the use of the object in this incredibly interesting picture. Thanks for trying! I only hope that someone with wheels will pay it a visit before long and ask the guy in a garage opposite where I think iron gates and such may be made. He was the one who told me what it was for but, as I say, the answer may also be found in the Helston Museum. I'll post an explanatory picture once this pic is fathomed. So far, you have earnt one and a half points!

Nancledra. It is or was for fitting cartwheels in, so you can adjust or add a new metal rim.

You've got it, CW! Such persistence! I shall put up the answer to this as Diagram to explain 'Lump in the Ground', Nancledra under 'Just for Fun' right now!