I second that! I've used this technique to remove broken drill bits and
taps from aluminum and copper. It does take time. My experience has been
with small parts that I could through in a beaker an a stirring
hotplate. I love to see that stream of bubbles coming from the hole as
the steel is disolved.
Alum???? is that the same stuff that they cook with, a taste less
product or is that short for aluminum somthing or other???????
not being funny, but i would like to know... and will it work with a
broken tap in a car engine???? (aluminum motor parts)....?????
thanks for a reply...
Ya, it's the same stuff. My part was small so I could put the aluminum in a
saucepan of almost boiling water. I mixed about 4 or 5 containers of the
Alum in the hot water, dropped in the part, set the heat to "simmer," came
back once in a while to stir the mixture (the Alum tended to precipitate out
of solution) and in about an hour and a half, the broken 2-56 tap had
completet dissolved. There was a VERY slight pitting of the aluminum after
the process but I managed to polish it out.
During the process, I could see bubbles coming from the hole containing the
tap. It was as though the tap was just "fizzing" away!!
Aluminum sulphate is available from garden centers to acidify soil for
things like blueberries. 5$ 5lb bag
It is also used for setting dyes when marbelizing fabrics Darma
Trading Co sells it. Find em online if the spelling is off look under
tie dye supplies.
If you can get to the upper end of the tap, TIG weld a small(1/4") nut
onto the end of the tap on the INSIDE of the nut. This will leave you the
shoulders to put a crescent wrench or socket onto to back the tap out. I've
had to do this many times, it is not uncommon to have to re-tack the nut a
couple of times to get the tap to back out. Welding it on the inside keeps
most of the heat away from the Al too.
Best of luck,
Jim C Roberts
email@example.com (richard) wrote in message
I had a similar thing happen and could not use a tap extractor. I
machined a simple hollow mill and cored out the tap, broke off the
cored section, and then tapped the hole over size and screwed in an
aluminum plug, drilled and tapped it to the correct size. Problem
solved and part saved.
firstname.lastname@example.org wrote in message news:
thanks for the suggestions. Someone suggested alum, funnily enough my
was here and he said "I think alum dissolves steel but not aluminium"
strange what surgeons know.. he then appeared with a couple of boxes
I haven't tried the alum, yet. I etched into steel recently
caustic soda[NaOH] and some volts. I cut ~.125" depth in no time in
Remebering that I knocked up a sort of clamp on tube, sealed to the
surface with an O ring, it will hold 50 CC of acid and it also holds
an electctrode. It's on the casting and merrily fizzing away at the
moment, I used battery acid as electrolyte.
The fact it's a roll tap obviously makes it slower to remove, though
it does help that I sprung for the tap with lubrication grooves,
sureely your likely to hydraulic in blind holes without them, after
all the 'cam height' of the lobed ones isn't eater than thread depth,
After an hour with 12volts and 2 amps, it's eaten enough to pick out
one fractured bit that I couldn't get out before. not that it looks
I couldn't feasibly weld to it, it would take a lot to unscrew it.
I tried a carbide mill, well the remains uf a broken one and I ground
it like a D bit and ran it backwards, well it got hot but didn't do a
stiff like a Bridgeport, no stiff like an Ajax.
a small tap busting edm seems the best solution, but it wouldn't get a
of action, I take the piss when I see people break taps. I haven't
it for so long.
The hole size for the tap is 8.7mm and I am drilling with an 8.6 and
getting 8.6><8.65, it's a bit stiff but I get a very nice fit like
which is just what I wanted. I have to do a circle of 12 in each
and I was doing a batch of 5 castings, I spose the most likely thing
got sloppy and didn't drill the hole deep enough. Well that's the most
likely explanation. That combined with the tap in an er collet meant
Still I have done 22 casting that are spot on, so one mistake, that's
correctable, isn't to bad..
I am going to up the drill 2 thou and see if that makes it slightly
what do you do if you want tight threads, I have the catalog's from
osg, dormer, presto and fette they only list one tolerance?
You do know that caustic soda is used to etch aluminum? Creates hydrogen
IIRC you are tapping 3/8-16. Balax says .344 diameter for a 75% thread,
and you are drilling to .338/.340? Do you need to have an 85 or so %
thread? You might try using OSG AL type cutting taps. They have a short
length of thread, helical style, with relief above. They pull the chip
out of the hole and work very well. I use them regularly.
What to do for tight threads. I guess you could keep drilling the holes
small and take your chances. Get some Alumatap, A-9 is pretty good, but
I think Alumatap is a little better. Maybe kerosine, but I don't recall
ever using it for form tapping, cut taps, or other 'cutting' operations
it works great. And stinks, and a PITA to wash off.
True. One of my most memorable and favorite aromas was going to the gas station
early on a weekend morning with the old man to fill 'er up. Well before
unleaded gas, that was. Kerosine smell is not bad, I find it really sucks to
get it washed off.
On 21 Feb 2004 18:44:48 -0800, email@example.com (richard)
Perfect! Sulfuric acid, with the workpiece positive will anodize the
aluminum, but etch the iron tap. After a few minutes the aluminum
will become insulated and no current will flow from the exposed
aluminum..only the tap.
On 21 Feb 2004 18:44:48 -0800, firstname.lastname@example.org (richard)
The part of the tapped hole that SHOULD be making the tap a tight fit
is the pitch diameter, not the minor diameter. Decreasing the tap
drill size when using form taps has a dramatic effect on the minor
diameter and the torque required to tap the hole. In a 3/8 -16 form
tapped hole .3431 gives 75 percent thread, while a .3474 gives 65
percent and .3516 gets you 55 percent. Usually, form tapped holes are
tapped to 65 percent. You can see that it is possible, with a form
tap, to have the tap fitting so tight that the metal has no where to
go but ahead of the tap. This reduces the hole diameter ahead of the
tap more and more until the torque required is greater than the
breaking point of the tap. Looking at the MSC catalog shows that form
taps start out at the H5 designation which theoretically puts the
tapped hole at .0025 above basic pitch diameter. The fit will usually
be tighter. That's why form taps start out at H5 but cutting taps
usually start at H2. You can order taps ground to smaller H numbers
from MSC. They are not that much more expensive than regular taps.
Reduce the tap drill size accordingly and you will get the tight fit
you want along with increased tap life. You should get more way than
264 holes out of 1 tap. When first starting to work in a machine shop
I tapped over 11,000 holes with one 10-32 roll tap. These holes were
about 3/8 long and were through holes. The holes were drilled to give
70 percent thread. However, the castings were die castings of aluminum
and were good castings with no hard spots etc.. Also, I just tapped
'em. The setup was done by the boss and the holes drilled by someone
with experience. I do know the holes produced 70 percent theoretical
threads though. We had class after work and since I was doing all
those holes I learned all about the hole size , cutting oil, speed
etc. It was my job to inspect the hole size with pins every so often
to double check the inspections done by the guy drilling the holes.
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