DPRG mailing list archives: [DPRG] Broken tap

Fri Feb 9 22:07:05 CST 2007

Or muriatic acid which will attack the steel tap and leave the aluminum
plate alone.  Works best if heated ever so slightly above room temperature
80~90degrees.  There is quite a bit of information if you goggle on
"aluminum muriatic acid tap removal".   This method is pretty painless, oh
and fun.

Or take the whole thing over to a job shop and have them throw a sinker EDM
machine at it.  Many of them are designed specifically for eroding away taps
and have swivel / swing arm heads and can be rotated around to work on items
that can't easily be lifted onto a table or into a tank...  This method is
quite a bit faster than the above, but will cost more, depending on the job
shop.  It may only take 3 minutes or les to spark erode the tap, however
some job shops have a $35~$55min.

I have performed both of these methods and they both work well.

My experience with smaller sized tap extractors like #6-32 &  #4-40 were
unsuccessful and I moved quickly to the methods above.  I did have
reasonably good success with tap extractors on larger sizes of taps.

Interesting note:  A little over 10 years ago I worked for an aerospace
company and one of the products we designed and sold were winglet sets for
hyper sonic wind tunnels.  A winglet set is a set of just over 6,000 fins
all with slightly different shapes used to move the air streams around
corners (old fashion recalculating tunnels and down feed tunnel corners in
modern wind farm straight shot collector style tunnels.) without going into
rotation.  Anywho, In a highly automated 5 axis CNC operation one of these
winglets took ~35minutes to produce.  Each of these winglets had ~1 dozen
fine pitch small tapped holes that used standard cutting taps on a hard
cycle as opposed to material displacement taps.  Even with the high cost of
run time and operator time a small amount of engineering analisys showed it
was cheaper to throw away the part and start over from billet rather than
send a machinist off to do the work.  Of course the machine isn't running
while he is off running an EDM or doing setup, etc.  But still an
interesting note.  Of course there are often times when the labor is
undervalued or the work piece exorbitantly prohibitive to replace, and then
again you may just be a student working on a home project with no budget at
which point, one of the first two methods comes recommended.

-Kenneth

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
Behalf Of Jon Hylands
Sent: Friday, February 09, 2007 5:26 PM
To: Eric Sumner
Cc: dprglist at dprg.org
Subject: Re: [DPRG] Broken tap

On Fri, 9 Feb 2007 16:38:50 -0600, "Eric Sumner" <kd5bjo at gmail.com> wrote:

> While working on this project for SMU, I broke a 4-40 tap while
> tapping a hole in 1/4" Al plate.  What is the easiest way to get the
> remaining part of the tap out of the hole?  I can't easily get to the
> underside of the plate (but I probably could if I have to), and there
> isn't enough of the tap sticking up out of the plate to grab with
> pliers.

You need a tap extractor.

Go to http://www.smallparts.com and type in: TE-043 into the search box
(assuming its a 3-flute tap).

A tap extractor is nice to have, but in reality you might be able to stick
a piece of piano wire down the slot made by each flute, and then using a
pair of pliers grap all three pieces and try and unscrew it.

Later,
Jon

--------------------------------------------------------------
   Jon Hylands      Jon at huv.com      http://www.huv.com/jon

  Project: Micro Raptor (Small Biped Velociraptor Robot)
           http://www.huv.com/blog

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