Arvid,
It is a long time since I had to think so hard, but I think although it is a good idea I don't think it will work how you think it will.
The nut will always see the 400lbs - even if the force in the air cylinder is 400lbs the nut sees 400lbs from the top and 400lbs from the bottom might make things worse.
That's how I am looking at it - does anyone else see it the same?
There again I could be completely wrong and up the river without a paddle
DaveH
I am thinking more along the lines of a couple of hydraulic cylinders on either side of the knee to act as simple "load balancers" that would supply a constant "upward" force of say, 300 lbs so that the bearings would only be "seeing" a hundred lbs of load.
Sort of like the hydraulic cylinders on a truck bed cover to allow you to lift it by hand or the same principle that garage doors use (yes I know it's a spring and not hydraulics) to "balance" the load so that the opener doesn't deal with the full weight of the door.
With a system like that you wouldn't have to synchronize two different systems as the hydraulic "lift" would be passive.
Hopefully that made some sense.
-Ron
I have played around with tail gate struts on my mill
The differance a 300 pound strut makes to manually lifting the table is simply amazing
Once i get my new lead screw finished i will be adding a gas strut to reduce the weight i have to lift
Dave, I think Arvid"s idea should work. If you put enough air pressure on the cylinder it would lift the ball nut off its thrust bearing. The ball screw will always see the table weight above the nut, below the nut it sees the lift of the piston. The difference is what the nut has to lift.
Greg,
You may well be correct, it is just I cannot see it. I think my brain cell is getting to old for this sort of thing
If the cylinder provides an up force of 400lbs and the table force down is 400lbs - the difference is 0lbs so you are saying the nut only has to lift 0lbs.
You could be right, but I still can't see it
DaveH
I like arvid's plan too, but my head is hurting a lttle now. I better have a drink.