Mechanical puzzler

Air spring? A pneumatic cylinder between the two plates connected to a reservoir precharged to give 500 lb force. The reservoir needs to be large enough relative to the volume of the cylinder so that compressing the cylinder does not raise the pressure in the cylinder/reservoir system too much.

This is a common setup on cam operated machinery in place of springs.

Another possibility is a preloaded spring. If, to take an extreme example, you used with a spring with a free length of 112 inches and a spring rate of 5 lb/in you'd have an initial force of 500 lb and a final force of 520 lb. Whether you can find/make a real world spring(s) that will fit in your mechanism is another matter, but worth investigating.

Ned Simmons

I like the gas spring idea. I've been thinking about them recently and they seem like a good answer to applying a constant load. ERS

Is there an indusrtial eq. to the gas springs that hold up my hood?

Yes, for example...

Ned Simmons

If you're going to be doing this have a look at the reservoirs Bimba offers. They're built like the SS body Bimba cylinders, can be ordered in many sizes, and are relatively cheap. I think Numatics offers something similar.

Ned Simmons

Easy peasy -- but finish your dogburger.