A lot depennds on what you are using them for If you work mainly in brass carbon taps and dies are adequate

if used with care

Roy

Cost of HSS taps vary very widely. They come in 2 style, ground thread and cut thread. There are also variations in the grade of HSS used. They needn't be expensive, these for instance which in real terms are ok

**LINK**

In terms of ground and cut thread one thing I have noticed is that taps these days tend to measure slightly over size. I'd guess this is some sort of standard where as some time ago taps tended to measure exactly on size. Same sort of idea as a reamer – the size they produce is very slightly greater than their diameter.

Dies come with the same variation except at very small sizes I doubt if ground thread can be found. BA for instance are usually all cut thread. The other difference is button and split dies. Personally I will only buy split as they can be adjusted a little if the usual die stocks are modified.

The problem with carbon steel taps and dies is that often especially in sets they aren't made very well. In the past there have been high quality ones available. There probably still are from true industrial suppliers but they will probably cost more than cheap HSS.

Well made carbon steel taps and dies are fine on most materials but can be a problem on materials like stainless steel. The other aspect is how often they are used as they will wear out more quickly than HSS. The harder the material the faster they will wear out.

I recently bought a cheap used set of M8x1.25mm left hand thread taps and a die in carbon steel. Made by these people

**LINK**

The fact that they are carbon steel doesn't bother me as they wont be used very often. They are dead sharp and accurately sized by modern standards at 8.05mm dia. For odd jobs I would still buy carbon steel if the price is right and the quality adequate. Breakages of both types really depends on how they are hardened. The usual reason for breakages in very small sizes is twisted holes down to poorly sharpened drills / drilling machine spindle not being square to the work / the tap being put in at the wrong angle and aspects like that.

Cheap carbon steel full sets ? I needed to cut a few UNF sizes some time ago and thought why not so bought a set. The holders were pretty useless and worse still the dies especially wouldn't really cut. The taps could with a lot of force. I didn't go for the cheapest of the cheapest either. These days I would just buy the ones I needed rather than doing the same thing again. Although I work in imperial the majority of my taps and dies are metric. If I was following some design that wanted say 1/4in BSF I would simply replace it with M6 if I needed to. BA can be replaced easily. I also have most of the usual sizes of ME especially in 40TPI. ME is unique and can't really easily be replaced with standard metric taps and dies.

Thought I had better add why the set was so bad. I suspect that they had never been near a grinder even for final sharpening along the flutes. Something to watch out for when buying.

John

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Edited By John W1 on 11/08/2015 10:35:25

Might be good way of getting them to the size they should be Neil with a suitable jig.

Size wise those Arc taps don't seem to be any better or worse than others. I'd guess more could be paid for them elsewhere.

I bought most sizes just in case I need to tap stainless again. If I needed to do that often I would be looking for HSSE/5% cobalt or even M42. One size was out of stock and I sort of requested they sent me them FOC for postage at least when they are back in stock – Fat chance.

John

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I think carbon steel is usually cut thread whereas HSS is ground thread which may account for the difference in the finish of a thread.

That's because threads are specified with various tolerances of fit. The most common, for general purpose use, is ISO2, aka 2B or 6H depending upon the country of origin. This is what you normally get if no tolerance is specified when buying. To ensure fits with most externally threaded parts taps are usually ground at the upper end of the tolerance, ie, oversize. It also ensures a longer life, as the tap takes longer to go out of tolerance as it wears.

Better quality taps have the tolerance grade marked, like this tap I bought recently for work:

Andrew

One thing that was emphasised in the documentation that I reviewed to check my facts is that taps do not cut to a specific tolerance, as there are too many variables, and no adjustment, unlike when producing external threads. Internal threads are also extremely difficult to measure directly. The standard method to check tolerance is to use a go/no-go gauge. For such a seemingly simple mechanism screws threads are pretty complex when one digs down into the detail.

Andrew

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I propose a big vote of thanks to Sir Joseph Whitworth

… and a round of Jeers to those who messed-up his work.

MichaelG.

If ever you wish to produce a slightly smaller size tapped hole to give a "snug" shake free fit on a commercial bolt/screw, then using the number 2 tap from a serial tap set ( 2 rings) will give the desired result.

Ajohnw reply interests me as I want a set of ba taps and dies for use on gm.cast iron.brass and maybe mild steel..I m thinking of Soba ?50 set assuming they are better than most Asian taps and dies..Came across HQS and wonder if they are better..cost about twice as much but thats ok ..I intend to use them quite a lot..Trouble is half a dozen hss taps cost as much as the Soba set..I d be grateful for any help..Jon

YeYes.I dont think there s anyway around it-buy 2 at a time..Its the whole range I m looking for 0-10 ba..Back to ebay and fingers crossed.Thanks for the reply Bill