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HSS or CS taps and dies

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AdrianR20/05/2019 12:58:48
597 forum posts
36 photos

Up to now I have used inherited imperial taps and dies, all of which just work perfectly.

Having just wasted £15 on a set of metric cheesium which went blunt after 3 turns in mild steel. (I know I should not have bought them but i wanted to make some T nuts to get started on my mill)

I am now looking at getting some reasonable metric taps and dies, and recently have been reading Tubal Cain's book about hardening and tempering. In that he says that Carbon steel can be harder than HSS if kept cool. Hand cutting a thread at most will only get warm, so what would be better, CS or HSS?

Looking at Tracy Tools I can get a loose set of CS taps for £20 or £40 for the HSS, any thoughts?

Georgineer20/05/2019 13:07:49
589 forum posts
33 photos

My brother's model engineering business uses a lot of small taps and dies. After many years of experience he uses only good quality carbon steel taps as they keep their edge better. I don't know who his supplier is.


Alan Waddington 220/05/2019 13:10:23
523 forum posts
88 photos

Was in the same boat recently, needed to tap some 5/8 20tpi cycle threads and my drawer full of miscellaneous, randomly accquired taps was not forthcoming.

Due to the price of HSS i bought a set of three carbon taps from RDG for the princely sum of £12.46 and so far they have performed faultlessly, im using them in Stainless Steel, which is hard on the best of tooling.

Andrew Tinsley20/05/2019 13:26:39
1611 forum posts

I am not sure about intensive use, but CS taps that I have (Tracy Tools) cut better in most materials than similar HSS taps (again good quality ones!)

I have never broken any of my CS taps but I have managed to break an awful lot of HSS ones! Maybe it is just luck, but I don't think so. If I were using them day in day out, then perhaps the HSS would prove the better bet, but for occasional amateur use CS taps seem to be the ones to go for.

Now I shall probably be shot down by the more experienced folk.


Thor 🇳🇴20/05/2019 13:29:01
1658 forum posts
46 photos

Hi Adrian,

I have bought several CS taps from Tracy Tools and they have worked well for many years. They have mainly been used for tapping in gunmetal and brass as I have a set of serial taps I use for steel.


Roderick Jenkins20/05/2019 13:32:33
2201 forum posts
616 photos

All the above is true. I am a great believer in CS taps but there is no doubt that they are generally more brittle than HSS so are more inclined to break in the smaller sizes. This happened to me recently with an M3 tap into mild steel. The lump was awkward to hold in my tapping guide so I was doing the job by hand in a vice. The plus was that because the tap was CS I was able to heat the whole assembly up to red heat and drill out the now softened tap. Mind you, when I bought a replacement tap it was HSS.frown

I've never claimed to be logical.


Edit: Why am I so crap at proof reading my own work?

Edited By Roderick Jenkins on 20/05/2019 13:34:20

SillyOldDuffer20/05/2019 13:42:46
8877 forum posts
1998 photos

The main benefit of HSS over CS is that it retains its edge almost up to red-heat. Thus HSS makes it possible to cut metal fast hot with a powerful machine. You can get equally good results out of CS by keeping it cool, and it's especially good for hand tools. But another advantage of HSS is that it's tougher - less brittle - than Carbon Steel, and should last longer in a busy workshop.

As you've found not all steels are equal. I've found very cheap taps and dies work well on soft metals like aluminium or dead mild steel. When sharp they do OK on brass, but they are easily blunted by mild steel or indeed any hint of heavy work. They tend to snap like carrots if you don't cut absolutely straight.

With one exception, I've had reasonable service out of moderately priced rather than very cheap sets. My requirements being genteel, I mostly use CS taps and dies, buying replacements from Tracy Tool's inexpensive range. Probably HSS isn't worth the extra cost for me because I don't do much threading and I avoid work hardening metals like bronze, stainless steel and unknown scrap. I usually make sure rods are a shade below theoretical diameter, and drill tapping holes slightly too big: this reduces the strain on taps and dies considerably without making threads significantly weaker.

Not been disappointed with anything from Tracy Tools, but there's a reason high-end taps and dies are eye-wateringly expensive.

Are you the type who likes tools to last forever? I tend to see them as disposable, which isn't to everyone's taste!


Brian H20/05/2019 14:13:30
2312 forum posts
112 photos

I've always been please with taps & dies from

The Tap and Die Company

No connection etc


Clive Brown 120/05/2019 14:25:15
863 forum posts
47 photos

IMHO both hss and cs tapsof good quality are suitable for the type of ME work that I do. I have both sorts, acquired as needed but mainly cs. I believe that hss taps are usually produced by thread grinding, whereas cs taps are cut threads. Grinding does, I understand, produce a thread-form to a tighter tolerance and possibly with better relief angles to the cutting edge, so is better for high class work.

I doubt whether the red hardness of hss is often called into play, certainly not in my workshop!

That's my tuppenceworth,


Edited By Clive Brown 1 on 20/05/2019 14:26:03

Howard Lewis20/05/2019 15:22:02
6305 forum posts
15 photos

HSS tends to be my choice, to minimise breakage. (And, Yes, I do expect everything to last forever!)

Wherever possible, I use Taps in a home made Tapping fixture, or guided in the machine, either hand driven, or at low speed under power, (using the Jog facility on the VFD).

Have had good service from both Tracy and Tap and Die Co, so happy to recommend as suppliers.


Sandgrounder20/05/2019 15:45:06
248 forum posts
6 photos

I may be wrong, probably am, but I thought that 'red hot' would refer to the cutting edges when looked at from a microscopic point of view, although the tool as a whole would appear just warm, the working edges could have been overheated and softened.

Andrew Johnston20/05/2019 15:49:01
6668 forum posts
701 photos

Personally I don't buy from TT anymore - chipped the teeth on too many taps. My old ME thread sets are undoubtably CS, as are some of my very old secondhand taps. But the vast majority of my taps and dies are HSS. I buy from professional tool suppliers, and I tend to buy spiral point or spiral flute taps as I do a lot of machine tapping, so CS items are simply not available.

I'm not convinced by statements that CS is harder and/or sharper than HSS, at least without qualification. Hang on while I get a beer and let battle commence. smile


Andrew Johnston20/05/2019 15:53:00
6668 forum posts
701 photos
Posted by Roderick Jenkins on 20/05/2019 13:32:33:

Edit: Why am I so crap at proof reading my own work?

I blame quantum effects. When one proof reads, the words have both the correct and incorrect spelling. Since one has a priori knowledge of what was written one sees the "correct" spelling. It's only once the "post" button is pressed that each word has to make a decision, and some choose to use the incorrect spelling.


Bill Phinn20/05/2019 16:11:43
768 forum posts
114 photos

Adrian, my go-to taps are Presto HSS

I would be interested to know what taps (i.e. brand/range) Andrew prefers and who the "professional tool suppliers" are he buys them from.

Nealeb20/05/2019 16:18:52
99 forum posts

The mention of spiral point and spiral flute drills is useful as these do not seem as well-known to the amateur (which I am as well - just had the good fortune to be told about these). Although nominally "machine taps", they work well for hand tapping as well, and generally are faster as you do not need anything like the same to-and-fro motion to break and clear chips or need swapping taper/second/plug. A while back, I had a fair number of M5 through holes to tap in something like 7mm mild steel. Spiral flute tap in cordless drill, touch of tapping compound for each hole, simple tapping guide to hold tap vertical (short stub of steel with clearance hole for tap and faced off square) and away I went. I use these down to M3 in preference to conventional hand taps. Spiral point for through holes, spiral flute for blind holes (although these do need a bit more care to stop chips jamming in the flutes - but still better than hand taps).

Chris Evans 620/05/2019 16:22:05
2067 forum posts

Always HSS for me, I once bought a set of carbon taps from RDG 5/8 x 26tpi. I only had one hole to do in 303 stainless but the taps could not manage it and I had to go HSS.

AdrianR20/05/2019 17:56:02
597 forum posts
36 photos

Thanks for the advise. I have always bought reasonably priced tools, then if I use them enough to break/wear them out think about buying a better quality ones. It sounds like CS will be fine for me at the moment, I will only work on brass, mild steel and CI.

I have never looked at the tap and die company, I will give it the once over. The reasons I picked TT were I have used them before and they offer a loose set of taps/dies. I have a draw full of tap and die holders, don't need any more.

Andrew Johnston20/05/2019 21:38:10
6668 forum posts
701 photos
Posted by Bill Phinn on 20/05/2019 16:11:43:

I would be interested to know what taps (i.e. brand/range) Andrew prefers and who the "professional tool suppliers" are he buys them from.

For my most used taps (metric, mostly for work projects) I go to my local tool supplier (CIS) - brands are Guhring or Dormer. For other taps I use Drill-Service, brands vary but OSG and FEW are common. On the very rare occasions I need a 32tpi ME tap I haven't got I use Tap & Die.


Andrew Johnston20/05/2019 21:41:52
6668 forum posts
701 photos
Posted by Nealeb on 20/05/2019 16:18:52:

Although nominally "machine taps", they work well for hand tapping as well, and generally are faster as you do not need anything like the same to-and-fro motion to break and clear chips or need swapping taper/second/plug. A while back,

Quite so. thumbs up

With spiral flute taps I find that in ductile materials the "swarf" comes out as a continuous ribbon, one ribbon per flute. Very little, if any, swarf remains in the hole. This is true wih hand tapping as well as machine tapping.


Emgee20/05/2019 22:15:48
2445 forum posts
291 photos

Check this video at 5 mins in to see what Andrew describes re swarf coming out as one ribbon per flute.



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