Night Vision Barrel

This part was a component of a night vision scope that was used in Viet Nam.  It presented its own unique manufacturing challenges to Grindley.  When we looked at the part we knew the problems that we would face would be in holding the thin walled section to print.

    First we turned the OD to print and drilled an 1½" hole through the part.  The part was threaded and diameters were finish turned.  Now came a problem.  We wanted to finish the ID but how were we going to hold it?   Collets didn't come this deep and a 3 jaw chuck would distort it.  So Bob decided to build a hydraulic pot chuck.  This consisted of a steel jacket into which was fit an aluminum sleeve with about 1/16" wall with O-rings on either side.   On the back of the jacket was a reservoir of hydraulic fluid that was capped off by a set screw.  The ID of the aluminum sleeve was a very close fit to the OD of the part.   When the screw was tightened it forced hydraulic fluid between the thin walled sleeve and the steel jacket forcing the sleeve to collapse on the part.  The result was consistent pressure around the part that allowed us to machine the ID without distortion.

    Next we had to machine all the holes.  Again the concern was distorting the thin wall.  We knew that it would have to be very light cuts.  So Bob designed a solid spud to hold the part and on the opposite end a pattern of the holes and cutouts.  These were then machined on a pantograph using a small end mill.