Out of curiousity, have anyone tried to counterbalancing a heavy Zaxis by using
a pair of slim, pneumatic or hydraulic cylinders.
Springs pulls harder the more you stretch them, and gasprings... are they slow?
One cylinder to push the axis up, and the other one placed somewhere "out of sight", with a weight on it. Or are gas springs both fast and reliable for a small milling machine?

But..ifi really need a counterweight for this little machine, i probaly overloaded a weak unsupported X-axis anyway. And finding space for a cylinder can be tricky enough. (http://home.online.no/~resagen/fres6.jpg)

You can get constant force springs, which roll up, like a tape measure.

A properly designed spring (mechanical or pneumatic) should be usable. Hydraulic would be too slow, gas charged like an automotive shock might work but I thing it would create too much resistance and prematurely wear things out.
Weighted counterbalances are used because they are pretty much fail safe and linear in force.

I ran a large router many years ago which used 2 large cylinders attached via chains to the Z slide. The cylinders were horizontal on top of the slide with chains routed around idler pulleys at the front edge, then the chains were attached to the Z slide. Pretty clean set up. The couterbalance pressure was, of course, adjustable which made the very heavy slide effectively weightless. Very cool set up and 'dumb' controls. Could be easily scaled to suit the application.

Hydraulics wouldn't necessarily be too slow, but messy, possibly expensive and overkill. Automotive shocks? - - not enough engineering data or options available to make the right selection for your application.

Adjustable retractors could be used - similar type springs found in a tape measure. These would probably work nicely.

Scott

A properly designed spring (mechanical or pneumatic) should be usable. Hydraulic would be too slow, gas charged like an automotive shock might work but I thing it would create too much resistance and prematurely wear things out.
Weighted counterbalances are used because they are pretty much fail safe and linear in force.

Hi,
McMaster Carr supply company (www.mcmaster.com) has a wide selection of the gas charged type springs, just weigh your whole Z assembly and order a spring with the same lifting pressure.
They are very easy to install, cheap, and I get 2-3 years of use from each one.
Just watch for oil leakage around pushrod of the cylinder and replace right away.
Dean

You can get constant force springs, which roll up, like a tape measure.

Ah yes. I had completly forgotten about that type. Should fit nicely on the back of my z-axis, and a small string are much easier to fit in then a bulky cylinder. Thank you all, have given me a broader view on things. My ballscrews arrived today, a rolled, cheap, preloaded comtop. They need a little bit of force to rotate, so well.. Guess i can make fitting for a pulley or two into the parts i have yet to make, in case i need a counterweight device of some sort.

Thanks.