FILENAMES:

Making_a_tap.jpg
Making_a_tap.gif
Making_a_tap1.jpg
Making_a_tap2.jpg
Making_a_tap3.jpg
Making_a_tap4.jpg


DESCRIPTION:

These are pictures showing how to make a tap.

Posted by Ted Edwards <Ted_E@telus.net>. 

The following description was provided:

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                        Making a 1/4-18 Tap
                   Ted Edwards, Ted_E@telus.net

Associated files:  Making_a_tap.txt, this file
                   Making_a_tap.jpg, the end result
                   Making_a_tap1.jpg, single pointing the thread
                   Making_a_tap.gif, figuring the groove depth
                   Making_a_tap2.jpg, milling the groove
                   Making_a_tap3.jpg, tempering the tap
                   Making_a_tap4.jpg, cutting off the wing nut blank

We have a beautiful oval oak dining room table.  The table proper is 
held to its pedestal by eight studs with wing-nuts.  Unfortunately one
of the wing nuts was missing when we got the table.  These have 1/4-18
threads which, while not unknown, is an unusal thread size these days.

I decided to make a wing nut to replace the missing one.  This meant, of
course, that I needed to make a tap with which to thread it.  Starting 
with a piece of 5/16" drill rod, I turned down an inch or so to 0.251" 
and tapered the end. I then single pointed an 18tpi thread on the 
relevent portion.

I really like the two flute taps I got from Boeing Surplus and decided
to have a go at making one of that pattern.  I played around with my CAD
program to discover that, for this size tap, if I milled a groove with a
7/32" ball end mill such that the deepest point of the groove was 0.048"
above the center line of the tap-to-be, I would get an approximately 6
degree positive rake on the cutting edges.  This is a Good Thing.  See
Making_a_tap.gif.  Note the two red lines.  One is a radius of the tap
blank.  The other is tangent to the ball end of the mill.  I set up the
spin index on the mill and zeroed the quill DRO with the bottom of the
mill just on the point of a spud in the spin index.  I then proceeded to
cut the two grooves 180 degrees appart.  The tap was then turned end for
end and a square milled for a tap wrench.

It remained to harden and temper the tap.  I coated it with Joy
dish-washing detergent, heated it to a "cherry red" in the forge and
quenched it in mineral oil.  I cleaned up a couple of places so I could
see the colour and heated it on a lab hotplate to light brown.  See
Making_a_tap3.jpg.  This is a nice way to temper small objects as the
hotplate has a thermostat and is much more controllable that a flame.

Now all that was needed was the wing nut.  I silver soldered a piece of 
1/8" thick steel flat into a slot cut in the end of a 1/2" round bar, 
shaped the "wing" and cut off the blank.  The blank was mounted in the 
drill press vise and a #9 hole drilled.  I started the tap in the drill 
press to ensure it was held square and finished the tapping with a tap 
handle.

I have made a couple of taps before but this one is by far the sweetest 
cutting.  Perhaps this method will help somone.