Gas shock on knee - how?

[txcowdog]

Would someone kindly explain how I would add a gas shock to the knee of my Bridgeport knockoff? I see McMaster-Carr sells shocks but there has to be more than just tapping a hole in the side of the knee and mounting the other end to the base.

Thanks,
Bill

[JPMach]

Actually you don't want a shock.
The more compressed a shock gets the higher the pressure is, you need a constant force on the knee. What is commonly done for the heads of large wood routers is to mount an air cylinder on that has the proper stroke to go full length and enough area to support the load at say 80 psi. Then the air cylinder gets a pressure regulator on the input so that as the kne is raised it allows more air in to keep the cylinder at the same pressure, as the knee is lowered it lets air out to still keep the same pressure.

you will want to be careful in how you mount the cylinder though so that all you are doing is reliving the wieght and not twisting the knee. The knee on a bridgeport tends to tip away from the coloumn. If you put the cylinder out in front it may make the knee want to rock back and forthacorss the screw as the preload in the ways has been canceled. If the cylinder is close to the column then gravity can still keep the ways tight and not rock while still alieveating the load on the screw.

JP