At the last meeting, Alan May brought a wiggler center finder he had built. Wigglers work real well, but I prefer the pump center for most lathe work.
The pump center I built is shown in the photo to the right. Pump centers are used with a dial or test indicator to true up the center of punch mark with the center axis of the lathe. When using the pump center, do not allow the tool to turn with the work. As long as the tool is stationary, any error in the tip will not be translated to the indicator. In other words, a more accurate set-up can be performed. Depending on the strength of the spring used inside the housing, the pump center may be used to hold the work piece against the chuck on faceplate while adjustments are made. This helps free up at least one hand.
The outer housing of the tool is made from 1/2" mild steel. It is drilled and reamed to so that the center shaft can slide smoothly inside. The other end is center drilled. A slot must be cut though the housing for the retaining pin. The center shaft can be made from .375" drill rod. Machine a 60( point on one end. Drill through the shaft for the retaining pin. The retaining pin is a piece of .187" mild steel or drill rod. A couple of center punch marks in the side of the pin will help hold it in position in the center shaft. Find a suitable spring that will fit inside the housing so that when the tool is assembled it will take a few pounds of force to push the center shaft into the holder.
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