Shop Made Pump Center
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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