Subject: Broke tap off in hole - now what?

From: [email-masked] (Clay Timmons)
Date: 14 Jun 1996 14:09:30 GMT

I'm a metalworker wannabe and yesterday I had a
little oops.  I was tapping a 8-32 hole in some
aluminum and I broke the tap off.  It broke off
nearly flush with the surface so it is not possible
to grip it with pliers to remove it.  I thought
of drilling a smaller hole in the broken off
tap and using a screw extractor.  So far that
has not worked since the tap is made of metal
much to hard to drill easily.

Any ideas on how to remove a broken off tap? 

Any suggestions to avoid this problem in the future?

Thanks,

Clay Timmons   [email-masked]

---

From: [email-masked] (Edward Haas)
Date: 14 Jun 1996 08:11:49 -0700

Clay Timmons ([email-masked]) wrote:
: little oops.  I was tapping a 8-32 hole in some
: aluminum and I broke the tap off.  It broke off
	(SNIP) Lucky you: dissimilar metals means that there are 
chemical methods that will eat out the steel and leave the al. behind. 
Not clear on details, but others here will know...
: Any suggestions to avoid this problem in the future?
	--Yes: what kind of lubricant were you using and how deep were you 
tapping??
	--Also, just how far along in the machining process was this 
piece?? Remember: sometimes it's easier to toss the whole thing and start 
over, rather than wasting the little free time we have to salvage the part...
-- 
	"Steamboat Ed" Haas	:	Another proud member of 	
	COMING SOON		:	The Anti-Virus Vigilanties
	http://www.west.net/~steamer  	
		---Decks a-wash in a sea of words---

---

From: [email-masked] (Roger Mitchell)
Date: 14 Jun 1996 18:20:43 GMT

Nitric Acid will disolve the tap without doing in the aluminum. It would
take about a day to do it however. You might also be able to drill it using
a solid tungsten carbide drill bit and take out the pieces.

			Roger Mitchell
			Vice President and Master Mechanic
			Fort Collins Municipal Railway 
			http://www.fortnet.org/CITY/Trolley/

---

From: [email-masked] (James Kirkpatrick)
Date: 14 Jun 96 15:22:49 MDT

In article <[email-masked]>, [email-masked] (Clay Timmons) writes:
|>I'm a metalworker wannabe and yesterday I had a
|>little oops.  I was tapping a 8-32 hole in some
|>aluminum and I broke the tap off.  It broke off
|>nearly flush with the surface so it is not possible
|>to grip it with pliers to remove it.  I thought
|>of drilling a smaller hole in the broken off
|>tap and using a screw extractor.  So far that
|>has not worked since the tap is made of metal
|>much to hard to drill easily.

Well, this is actually covered in the FAQ, available via anonymous ftp
to plains.uwyo.edu in the metal directory, and indirectly via
http://plains.uwyo.edu/~metal.

41.  Removing Broken Taps

     No matter how careful you are, some day you'll break a tap and wonder
     how to rescue your workpiece.  There are several solutions that have
     come up in the past.

     a.  One way is Electric Discharge Machining, discussed elsewhere.
         If you have an EDM system, you're in luck.  Alternatively try
         to find a machine shop in your area that has one and will do this
         sort of work.  The basic idea is to spark erode away most of the tap
         (if small) or at least one part of it, so the rest can be removed
         by just picking out the remaining pieces.

     b.  There are commercial tap removers that have fingers which slip
         between the flutes, so you can grip the tap and remove it.  This
         may not work well on small taps, and you have to buy the remover.
         It may be possible to build one but it might not work as well.

     c.  If the workpiece is non-ferrous (and has no other ferrous pieces
         attached or embedded), you can mix up a saturated solution of
         aluminum Sulfate at 120 degrees F, and soak the workpiece in it.
         This should dissolve the tap in a few hours (or a few days at
         room temperature).  A plastic tray such as Tupperware is best.

     d.  Another person suggested nitric acid, if the workpiece is aluminum.
         Test it on chips to be sure it won't eat the workpiece.  If the hole
         is blind, you may need to force some circulation by pouring out the
         "spent" acid and re-immersing from time to time.  Note this is
         dangerous, nitric acid is nasty stuff; this might be best done
         outdoors to avoid damage to tools from fumes.

     d.  If size permits, grind out part of the tap with a Dremel tool
         or equivalent, with a suitable grinding bit.

     e.  In some cases, you can try to simply drill out the tap.  This will
         depend on how hard the tap is (mainly the core), and how good a
         drill you have.  It may be difficult to get a good start if the
         break is irregular or slanted.  You may end up breaking the drill.

     f.  Throw away the work piece and start over.

     g.  Of course the easiest solution is to not break the tap in the
         first place.  Use proper technique, lubrication, etcetera.
         Keeping them sharp has been suggested; Darex makes a tap sharpener,
         though it may be expensive for the home shop machinist.

---

From: [email-masked] (J. Kimberlin)
Date: 14 Jun 1996 17:15:42 -0700

In article <[email-masked]>,
>			http://www.fortnet.org/CITY/Trolley/

Cole's catalogue has said for years and years and years that the way to 
get taps out of aluminum is to soak the part in a concentrated solution 
of aluminum sulfate.  Isn't this in the FAQ Jim?  This works for all 
non-ferrous metals.  Just place in a plastic or glass pan and pour in the 
solution.  If you can't keep it at 120 deg F, just let it sit there for a 
week or so and the tap will be gone.

If I wanted to admit to being a Klutz, I'd tell you how many times I've 
done this successfully.

JerryK

---

From: [email-masked] (Craig C.)
Date: Fri, 14 Jun 1996 22:32:16 GMT

>: aluminum and I broke the tap off.  It broke off

We used to have this problem fairly often in the instrument shop that
I used to work in. We averaged about 4 times a month having to remove
a broken tap from a work piece. For taps smaller than 10-32, we just
tossed the part in our home-made EDM machine and burned them out. For
the larger taps, one of the guys could usually find a way to remove
it. 

If the part is not too far along to scrap, then that is probably the
easiest thing to do. If it was nearly finished, then look up a local
machine shop and see if they have EDM and will take on burning the tap
out, or you might be able to work the tap out using some very small
picks and  scribes. If you can get it to move a little, take the part
and heat it in the oven for a half hour or so and try to back the tap
out while the part is hot. Last option is to get copies of Home Shop
Machinist and build the neat little EDM machine that was the subject
of a series of construction articles. I think Popular Mechanics has
done one also sometime back...

Frustrating isn't it? Best of luck whatever route you take...

Craig

---

From: [email-masked] (James W. Swonger)
Date: 26 Jun 1996 14:00:33 GMT

In article <[email-masked]>,
Dave Keith <[email-masked]> wrote:
>In article <[email-masked]>, [email-masked] says...
>>
>> ...of the 6 or so (taps) I've broken off this week...
>
>WOW,  what ARE you doing ?  How many holes did you thread this week ?
>
>dave
>

 Project was the construction of steel double doors for a business, made
of 1/8" wall, 1" box stock and 1/16" sheet, and a full perimeter 
frame consisting of 3"x1/2" plus 1" box (for the jamb) verticals and
3"x1/4" horizontal members, welded up so that they could knock down 
and reassemble on site. The frame has to support the two 100lb (approx)
apiece doors from one side, one hung off the other. It's a pretty 
impressive weldment, which took me over 80 hours to fabricate.  

 Hinges alone were 48 tapped holes, inset burglar bars for the large
center windows another 28, handle/lock/bolt/misc hardware another 35 or 
so. I seem to get anywhere from 0 to maybe 10 before I break the tap;
moving toward the latter as technique and discipline improve. The
taps just don't seem to stay sharp much beyond that, and this is 
generic mild steel stock.

-- 
##########################################################################
#Irresponsible rantings of the author alone. Any resemblance to persons  #
#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
#sify this effect. Pay no attention to the man behind the curtain. Billy!#

---

From: [email-masked] (Dave Keith)
Date: 26 Jun 1996 18:20:04 GMT

In article <[email-masked]>, [email-masked] says...
>generic mild steel stock.

Thanks for satisfying my curiousity.  Sounds like impressive structure.
Having tapped in thin stock I know how dificult it is to keep the tap
square as you go.  Your comment about technique probably answers you own
question. It's the old adage "practice practice practice'.  It is anoying
when the practice becomes expansive though isn't it.

Thanks again,

dave

---

From: [email-masked] (ANNE B. WATSON)
Date: 27 Jun 1996 03:16:03 GMT

>
>Get a table of tapping drill sizes - but NOT an industrial one. 
>Industrial users have the technology to make clean threads in tight
>holes (i.e. machines, tapping jigs, etc.). They often aim to get
>up to 80% thread engagement.

Funny, I just jumped in here looking for a WWW source for tapping drill
sizes and this was the first message.

I tried a search on Yahoo,  nada   guess there are not any engineers with
web sites.

Guess I will just keep looking and if nothing shows up  will try the second 
most valuable resource site    the public library.
Anne
--

---

From: [email-masked] (Doug White)
Date: Thu, 27 Jun 96 00:44:26 GMT

In article <[email-masked]>,
   [email-masked] (Dave Keith) wrote:
<In article <[email-masked]>, 
[email-masked] says...
<>
<>In article <[email-masked]>,
<>Dave Keith <[email-masked]> wrote:
<>>In article <[email-masked]>, 
[email-masked]
<>om says...
<>>>
<>>> ...of the 6 or so (taps) I've broken off this week...
<>>
<>>WOW,  what ARE you doing ?  How many holes did you thread this week ?
<>>
<>>dave
<>>
<>
<> Project was the construction of steel double doors for a business, 
made
<>of 1/8" wall, 1" box stock and 1/16" sheet, and a full perimeter 
<>frame consisting of 3"x1/2" plus 1" box (for the jamb) verticals and
<>3"x1/4" horizontal members, welded up so that they could knock down 
<>and reassemble on site. The frame has to support the two 100lb (approx)
<>apiece doors from one side, one hung off the other. It's a pretty 
<>impressive weldment, which took me over 80 hours to fabricate.  
<>
<> Hinges alone were 48 tapped holes, inset burglar bars for the large
<>center windows another 28, handle/lock/bolt/misc hardware another 35 or 
<>so. I seem to get anywhere from 0 to maybe 10 before I break the tap;
<>moving toward the latter as technique and discipline improve. The
<>taps just don't seem to stay sharp much beyond that, and this is 
<>generic mild steel stock.
<
<Thanks for satisfying my curiousity.  Sounds like impressive structure.
<Having tapped in thin stock I know how dificult it is to keep the tap
<square as you go.  Your comment about technique probably answers you own
<question. It's the old adage "practice practice practice'.  It is 
anoying
<when the practice becomes expansive though isn't it.
<
I don't know if this will help, but Brownell's (the gunsmith supplier, 
address is in FAQ) sells a very nice tapping guide for around $30.  It 
doesn't take too many busted taps to pay for it, and I think I've only  
broken one tap in 15 years since I bought it.  It's a small block with a 
set of interchangeable sleeves to fit different tap sizes.  You can get 
it into places you can't get at using any of the larger tapping gadgets. 
 The one time I busted a tap, it was a 6-32, and I simply over-torqued 
it.  I've also found that two-flute spiral-point 'gun' taps are much 
easier to work with on through-holes than the regular variety.  They have 
more 'meat' to them, and are therefore more break-resistant.

Doug White

---

From: [email-masked] (Scott Logan)
Date: 27 Jun 1996 12:02:40 GMT

In article <[email-masked]>, From [email-masked] (ANNE 
B. WATSON), the following was written:
> I tried a search on Yahoo,  nada   guess there are not any engineers 
> with web sites.

Anne,

I'll bet there are!  First of all, try a better search engine, Alta
Vista

http://www.altavista.digital.com

With this, you can search not only Web sites, but also Usenet messages.

In the meantime, can I help you find a tap drill size?

--
>From  Scott Logan,
http://ourworld.compuserve.com/homepages/LoganAct
Reply to [email-masked]

---

From: PPIERCE <[email-masked]>
Date: Thu, 27 Jun 1996 07:03:55 -0700

> most valuable resource site    the public library.

I think I got a table with some tool or a drill set at Sears.  
Maybe a drill sharpening gadget.  Sometimes there is a table in a
drill index (box).

Paul in AJ AZ

FAQ

FTP://Plains.uwyo.edu/metal/

---

From: [email-masked] (Russ Kepler)
Date: Thu, 27 Jun 1996 19:02:14 GMT

In article <[email-masked]>,
>most valuable resource site    the public library.

What sort of thread form?  I believe that there's about 25 pages of 
this sort of information in _Machinery's Handbook_ covering most all
of the thread forms.  Metric is easiest to calculate, others a lot
harder.

---

From: [email-masked] (Dave Keith)
Date: 27 Jun 1996 22:18:25 GMT

In article <[email-masked]>, [email-masked] says...
>
>This is a multi-part message in MIME format.
>
>--------------7F7837374D44
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>
>ANNE B. WATSON wrote:
>> 
>> >

I seem to get tap drill info all the time.  In the back of the MSC catalog
for example.  I have several tables with columns for :

	decimal inch
	fractional inch
	millimeter
	number/letter drill sizes
	thread size

Since I only have fractional inch drills I just go to the next size up. This
has produced reasonable threads for #10 and 1/4" screws,  but they are less
than the 75% (?) thread that tap drills aim for.

dave

---

From: [email-masked] (Alan Shinn)
Date: Thu, 27 Jun 1996 18:42:25 -0800

In article <[email-masked]>, [email-masked] (ANNE B.

> most valuable resource site    the public library.

Anne:
When you find it, let us know ---I need (and can't find) the tap drill for
a 4-32.

---

From: Jim Sehr <[email-masked]>
Date: Thu, 27 Jun 1996 20:07:14 -0700

> In article <[email-masked]>, [email-masked] (ANNE B.

 When you find it, let us know ---I need (and can't find) the tap drill 
for
> a 4-32.
outside dia. .1120
pitch dia..0917
root dia..0714
TAP DRILL #45 .082 dia. 75%thd

                           [email-masked]
                           Broken Tap extraction
                           Downey Ca.

---

From: Roger M Weppelman <[email-masked]>
Date: 28 Jun 1996 13:32:00 GMT

r
>of the thread forms.  Metric is easiest to calculate, others a lot

I have always assumed that for 100 percent engagement, the tap drill is equal to the 
minor diameter; for zero percent engagement, it is equal to the major diameter, and 
every other percent engagement it is in between and directly proportional to the 
difference in major and minor diamters: e,g, for 50 % engagement, the tap drill is 
minor diameter plus 50% percent of the difference between the major and minor 
diameters. Is it more complicated that this?

Roger Weppelman

---

From: PPIERCE <[email-masked]>
Date: Fri, 28 Jun 1996 08:11:48 -0700

> diameters. Is it more complicated that this?

Sounds pretty reasonable to me.
Frank McLean gives a formula in his writings.
Also how diameter and machine screw sizes corelate.

Paul in AJ AZ

Tap Drill calculations
Per Frank McLean
The Shop Wisdom of Frank McLean (Village Press)

TD  = Tap drill diameter
SD  = Screw diameter
TPI = Threads per inch

TD = SD - 1/TPI

	Ex.  #6 screw diameter = .138 = (major diameter)
		where TPI = 32 

		.138 - 1/32   =
	      = .138 - .031   =
	      = .107
		
		#36 is .1065" dia

To find screw diameter (major diameter) of a machine screw
multiply the machine screw number by .013.  Add the product
to .060".

	Ex.	(#6 X .013) + .06 =
		= .078 + .06  = 
		= 0.138" (major diameter)

Easier to get a table.

Paul in AJ AZ

VILLAGE PRESS
	LIVE STEAM
	PROJECTS IN METAL
	HOME SHOP MACHINIST
	Also some Great Hardcover
	collections of reprints

http://members.aol.com/vpshop/index.html
http://members.aol.com/vpshop/pim.htm
http://members.aol.com/vpshop/hsm.htm
http://members.aol.com/vpshop/steambook.htm

1-800-447-7367

---

From: [email-masked] (Kevin AstirCS "1U" KO0B)
Date: Fri, 28 Jun 1996 12:51:21 -0700 (PDT)

I can never locate the tables, but I can usually find my calculator:

Inches:

Drill dia = Major diameter -  .7( 1 / pitch)

This is for 70% thread engagement.  Change the .7 to whatever you
want.

Metric:

Working in millimeters:
Drill dia = Major diameter - .7(pitch)

Same deal with that .7

Now all you need is a table that tells what diameter a #6 screw is.

What is the formula for converting these # sizes to inches?

-KF-

---

From: PPIERCE <[email-masked]>
Date: Fri, 28 Jun 1996 18:54:48 -0700

> What is the formula for converting these # sizes to inches?

Here it is  - posted last night.

Paul in AJ AZ

Tap Drill calculations
Per Frank McLean

TD  = Tap drill diameter
SD  = Screw diameter
TPI = Threads per inch

TD = SD - 1/TPI

		.138 - 1/32   =
	      = .138 - .031   =
	      = .107
		
		#36 is .1065" dia

	Ex.	(#6 X .013) + .06 =
		= .078 + .06  = 

Easier to get a table.

Paul in AJ AZ

---

From: Bernie New <[email-masked]>
Date: Fri, 28 Jun 1996 21:01:20 -0800

> multiply the machine screw number by .013.  Add the product

____________________

It seems like you would get a pretty good approximation to this by 
adding 5 to the machine screw size, and then dividing by 80. To divide 
by 80, first divide by 8 which at worst will leave eighths in the 
result. Convert this to decimal (I'm sure most of us know eighths by 
heart), and then divide by 10, by shifting the decimal over one place.

This works pretty well for a #6, but I haven't looked at how well it 
works for very large or very small sizes.

For a #6:

   6 + 5 = 11

   11 / 8 = 1-3/8 = 1.375

   1.375 / 10 = 0.138"

BTW: For those of you who followed the recent thread, I was taught these 
sort of approximation techniques back when I was using a slide rule.

Bernie.

---

From: PPIERCE <[email-masked]>
Date: Sat, 29 Jun 1996 11:02:29 -0700

Bernie New wrote:
>  I was taught these

That was the nice thing about sliderules and Simpson VOMs.  You could 
see where you were going or had come from.

I hung up my Pickett (it was a yellow one) over 20 years ago when the first calculator 
with builtin trig tables came out for $17...

Have a $12 Casio on my workbench and one here at my computer desk.

Still use a VOM (analog - not digital).

Paul in AJ AZ