"Dave Plowman (News)" wrote in message
...
In article . com,
dcbwhaley wrote:
Any advice on buying taps. I need sizes from 2.5mm to 6mm (including
3.5 mm - even though my local DIY shop tells me metric screws only come
in whole numbers) for tapping mainly aluminium and occassionally mild
steel.

MY internet search seems to find huge sets of taps and dies at
suspiciously low prices or individul items at pocket wrecking prices.
Materials seem to be carbon steel, tungsten steel and high speed steel.
Which is best?

I think you've answered your own question. For serious use you need
expensive HSS types. For occasional use where the thread isn't really
critical a cheap set might be ok - although they tend to vary somewhat.
I bought a Draper set in desperation one Sunday after 'losing' a
particular one I needed and they proved ok at the price.

Draper stuff is usually reasonably well made and serviceable. By contrast my
first set of cheapish carbon steel taps and dies bought many years ago
(can't be arsed to go to the garage to look up the make) was okish in the
larger sizes for cleaning out existing threads, useless in all sizes for
cutting new threads in anything (not sharp enough) and the first time I used
the 4mm tap to clean out a thread in a carburetor it buggered it completely
by cutting it massively oversize.

Since then I only use quality brands designed for real engineers. There's
nothing worse than trying to do a good job with crap tools. The OP wants
small sizes of taps and those are the worst for quality in cheap makes. A
few thou error on size in a large tap might go unnoticed. The same error in
a 2.5mm tap will mean the resulting thread is useless and strips the first
time you tighten a bolt in it.

You also break the small sizes more easily and that's where HSS instead of
carbon steel has a double benefit. Stronger and much less brittle and likely
to snap.

Anyway the OP can do what he wants but when you do this sort of thing for a
living you quickly find out just how expensive cheap tools are.

Another trap I fell into once was a set of 8 or so adjustable reamers at a
model makers exhibition many years ago. Quality makes like Taylor and Jones
are the best part of £30 each. This boxed set was £40 the lot and despite
huge misgivings I fell for it. What a bloody waste of money. The holders
were ground on the **** so all four blades didn't cut at the same time, the
blades were badly ground, blunt and snapped like carrots the first time I
tried to use them to ream out some bronze valve guides. I got no use out of
any of them at all in the end and the money was wasted.

However, each T&J reamer has given me years of faithful service before
eventually needing a new set of blades.

Repeat after me. Never ever ever ever buy cheap tools.
--
Dave Baker
www.pumaracing.co.uk
"Why," said Ford squatting down beside him and shivering, "are you lying
face down in the dust?"
"It's a very effective way of being wretched," said Marvin.