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.

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.

Thor

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!

Dave

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,

Clive

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

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.

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.

Andrew

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).

Quite so.

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.

Andrew

Excellent video, the swarf behaves exactly as I would expect with a spiral flute tap.

Andrew

A big generic difference between carbon steel and high speed steel taps is that carbon steel ones may have been turned then hardened, whereas high speed steel ones are almost invariably hardened then ground.