By: Dave Hammer
Treadle Push Rod Springs
The back pushrod is primarily made up of three pieces (not including the springs). The top piece connects to the rocker arm and is primarily a solid 1.5 x 1.5 bar (with some 1x2 solid welded to the top for linkage to the rocker arm) that slides down into the center piece. The center piece is a heavy 2" square tube. There is 3/4 inch solid square bar welded around the center tube for the center spring to sit on. The top of the center spring pushes against the linkage bars. The bottom piece of the pushrod is another solid 1.5 x 1.5 solid square bar. It pushes up into the center piece from the bottom. It is solidly connected to the middle piece by drilled holes in the middle and lower pieces. I use a 3/4" pin with a lynch pin to connect them together. I can have multiple holes in the center piece to adjust the length of the pushrod(I have only drilled one so far). The two side springs pull the top piece down. There is strong opposing action between the center and outside springs so the center spring is not compressed when I press the treadle until the hammer hits. The top springs are held by the linkage bolt on top. The bottom of the outside springs are held by bolts welded onto the center piece of the pushrod.
When the treadle is pushed down, it pushes up all 3 pieces together. When the hammer hits the target, the rocker arm stops (along with the top piece of the pushrod. The middle and lower pieces of the pushrod continue to rise against the center spring to cushion the stop. Does not give me a shock, and all that weight balances the hammer so it doesn't need much of a spring to pull it up. I also believe the weight of the pushrod assembly and rocker arm adds to the punch of the hammer.
The fourth spring you see in the picture (visible under the right outside spring), just pulls the hammer back up. It is connected to the rocker arm on top and the backbone on the bottom. The hammer will actually rise without it, but not quickly enough to suit me. It is a very light garage door type spring and offers little resistance when the treadle is pressed down.
Another picture provides a hand drawing of the pushrod parts.