A lot of the best taps are made by little industries nobody ever heard
of ... often on special contract to other industries and the
military/aerospace firms.
As for GOOD taps, check out any full machinist's supply catalog ... MSC,
J&L, etc. Be prepared to spend money. One really GOOD (depending on what
you want it for) 4-40 tap may cost perhaps $60.00. Let's not talk GOOD taps.
For model railroad usage any decent High-Speed Steel (HSS) straight
flute 'plug' length tap will do nicely. Cost is in the $2.00 - $3.00
range, each. For 'through' holes the 'spiral point' ('gun') style is
especially nice, and less prone to clogging and breakage. Cost is about
the same. To tap to the bottom of blind hole you'll also need a
'bottoming tap' ... cost is about the same. sometimes a decent used
highewr quality tap may be better than a new cheap one.
For a well rounded set you'd thus need three of each size, as listed
above. Sizes you'll likely need for model railroad use, in approximate
order of usefulness include: 2-56, 0-80, 1-72, 4-40, and 6-32. Thus five
sizes and three taps in each ... 15 taps total. You can buy them as you
need them. Many never need more than the 'plug' taps.
There are MANY, MANY other sizes and types. Most sizes are not likely
needed by model railroaders, and many are specialized types of taps
(different thread pitches, thread forms, shanks, tapers, lengths,
'thread forming' taps, etc.). There are also a similar bunch of 'metric'
sizes (that's every bit as big a 'swamp', just a different one).
As for breakage, the harder the tap the more easily it can be broken.
Often the good ones break easier than the cheap ones ... IF ABUSED.
Consider them to be made of glass. It's hard to break a tap by just
threading holes. Taps usually break from being twisted SIDEWAYS (bent),
not from over-torquing. They can also jam in the hole if the flutes fill
with chips. The tap usually needs to be reverse rotated a fraction of a
turn every couple turns forward, to 'break' the chips (except with 'gun'
taps). At the first sign of binding, back the tap out, clean the chips
from the flutes, and try again. If it's not going properly, determine
WHY. Something's WRONG.
Most tapping, especially in metal, requires the use of some form of
lubricant/cutting fluid. Such fluids include oil, wax, water, kerosene,
milk (yes), lard, and whole bunch of commercial fluids. Different
materials require different fluids. Yes, sometimes it can be done dry,
even with good success, but that's rarely the best choice in metals.
One of my lab assistants, a student, just completed hand tapping 400
plus 5/16-18 holes in 3/8 steel plate. He never broke the tap, but did
wear it out ... one broken tooth, and now quite dull. Such taps are even
then useful, for cleaning out rusted nuts and such.
Dan Mitchell
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Post by Greg ForestieriLooking for opinions on taps. I thought that as light a hobby as we
have any tap would do, I'm finding that not to be the case. I break a
Kadee tap about once a month, then I tried Dubro which promptly broke
on it's first use tapping *plastic*.
Taps - what brand is best?
thx
Greg