Modifying the Spindle Index Pin
 

    The headstock is fitted with a retractable Index Pin.  This engages one of Sixty (60) evenly spaced holes in the large spindle bullgear.  This allows you to index the work on the lathe.  The figure below shows a diagram of the pin and associated parts.

    The major problem with this pin, however, is that there is no provision to lock it in the retracted position!!  Proof that the pin can move while the lathe is running is amply shown be the damage to several of the holes in the backgear!!  Atlas does have a spring and ball-bearing that rides against the pin, but no slot on the pin to provide a positive hold!.  Therefore all the spring and ball do is provide a moderate prevention of vibration from causing the pin to move.  When changing the chucks it is all to easy to knock into the pin, and after several changes I can see how the pin can hit the gear, unintentionally.  Originally I had planed to simply leave the pin out, but it may come in handy.
    I decided to cut a grove in the pin for the ball to lock into.  The pin and associated parts were still in the plastic cup from cleaning, so I dug them out.  I inserted the pin and lightly inserted its' retaining pin.  The ball and spring hole is drilled through the top of the pin hole and continues past this hole.  The parts press on the pin from the portion below the pin and are inserted from the top.  With the pin in place I moved it slightly toward the gear.  Using a close fitting drill bit in the upper part of the spring hole, I marked the pin for the grove.
    I removed the pin and chucked it in a 3-jaw by the end opposite the knurled (handle) end.  This arrangement leaves very little of the pin clamped by the jaws, so care had to be used in the turning operations.  I originally tried to chuck it by the knurled end, but could not get it to run concentrically.  I used a carbide D type bit for the grooving operation.  This bit is shaped like a threading bit, but with a slightly rounded nose and broader cutting angle.  I positioned everything and started the grove, turning the chuck by hand.  After insuring that the bit and holder did not hit the chuck, I put the lathe in the lowest backgear.  By taking extremely light cuts I was able cut the grove.  After I had reached the depth I wanted I cut slightly towards the chuck to widen the grove.
    Next after moving the carriage away (and still in the lowest backgear) I used a round needle file to round out the bottom of the grove and remove the slight ridge at the edges.  This finished the modification.  Thinking back I should have cut a similar grove to lock the pin in the inserted position, but at this point with everything assembled I will leave it as is.
    Inserting the pin with the ball and spring in place was made almost impossible using just an awl to press the ball into the hole.  The pin has a reduced point to fit the holes in the gear.  This point kept pushing the awl away before the main body could reach the ball.  To get around this I cut a short length of brass tubing and pressed this in place with the remaining tubing portion.  During this I held the ball down with the awl.  The tubing then kept the ball retracted.  I then inserted the pin which pushed the tubing through the hole.  This allowed the ball to remain retracted until the pin body was in place to past over it.  The tubing piece must be cut so it will exit the hole completely before it contacts the gear!!  I then used medium strength Loc-tite to hold the retaining pin, in addition to the slight press fit.  This retaining pin is shown already in place on the above diagram.
    Now the Indexing Pin is retained securely by the ball until I need to use it.  A fair, but not, great force is now required to move the pin.  No more accidental engagements.

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