Hole Tapping Guide with Spring

The best way to manually tap a hole, when the part is still on the mill, is to use a shaft which has a tapered end.  The tapered end interfaces with the hole on the end of the tapping handle.  This ensures your threads are "perfectly" normal to the part.

While tapping a hole during the Simplex Engine Project, I realized I did not have this helping taping guide.  The simple way to go would be to use the shaft with the tapered end as I described above.  Using that way would force you to move the quill as the tap moves downward, but who wants to do that?  So I came up with a three-part (plus one screw) design that uses a spring to save me from that 'extra' labor.

Assembled Tapping Guide with Spring

To use it, simply put the non tapered end into your chuck, put the tap and tapping handle in place, and move the quill down until you have compressed the spring a reasonable amount.  Now you can rotate the tap with the tapping handle while maintaining some axial force.

Although the drawing uses 1/4 rod, I ended up using a slightly larger diameter since that's what I had laying around.  Whatever you choose, make sure it's small enough to fit in your chuck.

Tapping Guide Parts

Tapping Guide Drawing