On 2008-02-20, wrote:
Can anyone advise about what type of taps to get, pros cons of types
of tool steel in different materials etc.

I see many different taps, cheap chinese to top name brand, many
different prices. I know people say buy top of the range name brand as
you get what you pay for. But as a poor hobbiest my budget does not
strech to that.

I wonder what would be regarded as best all round material for a tap
and die set?

Don't *get* a set -- get individual taps as you need them, so
you can spend more on a given tap and get good quality. Granted, I have
a set of TRW taps and dies -- everything from 0-80 to 1"x8 with
starting, plug, and finishing taps and matching single dies. But I got
that from an eBay auction without a photo, and took a chance. The lack
of a photo scared off most other bidders, so I got it for a reasonable
price.

Any set which does not say the material of the taps is almost
certainly carbon steel -- the worst choice other than Chinese. Hanson
tap and die sets are a good example of those -- something to avoid.

I have seen tungsten, hss (in various Cobalt%), carbon steel, tin
coated, and others.

For that last specific, I presume that you mean TiN coated
(Titanium Nitride), not the metal Tin, which is pretty much useless as a
coating -- though cheap vendors sometimes mis-spell it that way, and
don't know the difference -- such as ones which I encounter at hamfests.

The basic principle with TiN coating is that it can be put on
high quality steels or on pure junk -- and the behavior is according to
what is on the inside, not the coating. The TiN coating reduces wear,
and causes some chip materials to glide along the edge and flutes
without welding to them thus dulling the tap prematurely.

Carbon steel is very brittle and is a poor choice, with only
junk steel from China being worse. The carbon steel will break in the
hole, and you are stuck trying to remove the remains without damaging
the workpiece which you may have many hours of work into already.

Solid carbide taps are very good for tapping hard materials, but
are also very brittle and will break easily with a bit of side pressure.

A Cobalt steel will probably be the best for most purposes --
but avoid those from China, as you never know what you will wind up
with. It could be good steel, or it could be total junk, and you won't
know until you have bought it and are trying to use it.

As long as you are tapping through holes, I strongly suggest
"gun" taps (spiral point taps) which chase the chips ahead of the tap
and avoid having to back up the tap every quarter to half turn to break
the chips.

Good HSS and Cobalt steel taps are ground threads, formed after
the material is hardened.

Cheap carbon steel taps are threaded, the flutes are cut, and
then the metal is hardened, often producing poor quality threads.

It is better to buy only the taps you need, but good quality
ones with each purchase rather than a full set of cheap taps.

TiN coating on a good tap (say Cleveland similar) can improve
the performance when power tapping. It is not necessary for hand
tapping. TiN coating on a junk tap is still a junk tap, and it is likely
to bend or twist when you are using it -- just as it would without the
coating.

I wonder what is best for taps and dies.

Is it more important to have a toolsteel that holds a very sharp edge,
is very hard, or is very tough.

It depends -- what are you tapping? Mild steel is pretty
forgiving. Already hardened tool steel requires special materials and
techniques.

Aluminum needs something like kerosene or WD-40 to keep the
aluminum from sticking to the tap -- even at hand speeds.

Taps cut very slow so heating is not a
problem.

Not always true. If you are tapping say 40 or more holes at a
time, you will eventually want to get a tapping head to mount in your
drill press or your milling machine. Those will tap at very high speeds
with quality taps and the right lubricant for the metal being tapped.
And here is where TiN coatings on good taps really starts to help.

Are there any tests to see what the quality is of the taps I
buy is?.

The price? Try using them -- after which it is too late to take
them back. I use the price, and absolutely avoid Chinese made taps or
drills.

What is most important thing to consider when buying a tap?

What material you are going to be tapping, and whether you will
be doing it under power or by hand. also there are tapping fixtures
which will reduce your chances of starting a tap at an angle or applying
side pressure and thus breaking the tap.

6-32 taps are going to be the easiest to break. The thread
pitch is too coarse for the diameter -- because someone sometime thought
that it would be nice to have the same pitch go through three sizes,
6-32, 8-32 and 10-32. The second and third are good ones, but you
*will* break 6-32s in your learning -- and even afterwards.

Does anyone have any references to books or web pages on the subject?

Contact places like Cleveland and Greenfield. They may have t
on their web pages, or may send it to you for free or very little.

How do I know when my tap of die has become blunt and how can it be
sharpened?

When it takes more torque to continue tapping the same material.
You may see the tap starting to wind up with the torque.

If you have a Tapping head like a TapMatic, you have a torque
limiting clutch on them, which you set to just a bit past the point
where a new tap stalls and slips the clutch. When the clutch starts
slipping, it is time to replace the tap -- and put that one in the
trash, or give it to someone who you don't like. :-)

I really know nothing about tapping other than it is important to
drill the right size hole, use plenty of cutting oil or tallow, and to
make sure the tap is centered and parallel in the hole.

If it is aluminum, use kerosene or WD-40. If it is something
which work hardens like stainless steels, cut fast and hard (tapping
head helps), use something like Molly-Dee (Molybnium DiSulfide) grease.
For many non-aluminum metals TapMagic works nicely -- especially if you
can get the old formulation.

I am initially wanting to tap mild steel but would be interested in
tips on tapping in all metals (stainless, high tensile, brass,
aluminum, etc..).

Each of which has its own problems and is likely to be best down
with its own particular flavor of tap and tapping fluid. Brass, you cut
dry. Stainless work hardens so you need to be careful to keep going,
and to have a compatible tapping fluid. Aluminum, as mentioned before,
wants kerosene or WD-40 (the latter in a spay can for convenience of
application, since it is mostly kerosene anyway. :-) Some aluminum
alloys tap nicely, others are gummy and very likely to mess things up.
For those, perhaps the best bet is to use a thread-forming tap (it does
not make chips, it just pushes metal aside to make the threads, so it
needs a different size tap hole than a cutting tap does.

Lots of things apply, and you asked a very general question, so
I had to type a lot of words. :-)

Good Luck,
DoN.

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