On Mon, 08 Sep 2008 10:37:12 -0700, JR North
wrote:

Have a project, need a gear for a stepper with .187" Dia D shaft. I can
make the gear; are there broaches for forming the pilot bore? Seems
there would be a bazillion different ones, depending on the width of the
flat.
Else, how to?
JR
Dweller in the cellar
============
The single flat D appears to be a driving method that was
developed early in the industrial revolution and is in the
process of being replaced with the double D as this allows for
balanced machining/less drift.

Much will depend on the material and set-up [and required
accuracy] but many years ago in producing an automotive part I
found out that the single D shape was hard to hold to an exact
location. The solution at that time was to form an oversized
blank, broach the hole, and then use the d-hole to locate from
for the required concentricity/axial runout.

If you have a small volume, no tooling, no press, etc. you may
want to consider OP [outside processing] by a broaching house
such as
http://www.centerbroach.com/4.html
http://www.minibroach.com/Tooling_neu.htm
http://www.buckeyebroach.com/rfq.htm


Rotary broaches are available for the double D.
http://www.slatertools.com/adjustmen...toolholder.htm
http://www.rotarybroaching.net/swissbroaching.htm
and several others
Thus you should be able to produce the blank in one operation at
the cost of slightly longer cycle time. Be reminded that there
will be a *SLIGHT* twist or helix in the formed hole which could
be a problem, or could make a nice snug press fit depending how
you look at it.

The standard D type broach tools are available from
http://www.dumont.com/prod7c.html
http://mdmetric.com/dumont/prod7a.html
be setting down when you check prices.

Another low volume alternative could be a bushing with the D hole
that you press fit /loctite in the blank.

also see
http://www.cnczone.com/forums/showthread.php?t=18170
http://www.janellestudio.com/metal/drilling_tips.txt {about 1/4
down page}

Good luck and let the group know how you make out.