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the old rule was try to keep one set purely for use on brass and never use it in steel – think this esp true of carbon steel taps/dies.

also try asking around in your local model engineering soc – BA and other older taps/dies (usually Imperial) often surface in rummage sales or possibly another member may have some spares

OK I will blow against the wind, as a toolmaker for 50 years and still messing around in retirement I will only buy HSS. I have only ever bought a couple of carbon taps in really odd use them once only sizes in brass or aluminium.

I have no confidence in using carbon taps that could easily snap and ruin hours of work for the sake of saving a little money. I do have access to a spark erosion machine to remove broken taps but would rather not take the risk.

I have almost always chosen to use Carbon Steel taps and dies and have found them no worse than HSS taps & dies. I was glad that I had chosen Carbon Steel recently when I broke a tap and had to drill it out using a carbide end mill.

Hi Chris,

Not blowing in the wind, I concur with you sentiments also from half a lifetime in Toolmaking. I will say that carbon steel taps obviously do work but from my home shop experience the quality is not good, generally the threads are machined then hardened & then the flutes are ground, HSS steel taps are ground all over after heat treat.

You pay your money & gets your choice.

Tony

As a metal cutting tool material Carbon steel has one huge disadvantage. It loses hardness when it gets hot and goes blunt, perhaps at temperatures as low as 120C. As its other properties are suitable Carbon Steel is a good choice for hand tools (like files) because they are unlikely to get very hot.

Tool bits in a machine are a different matter, They can easily get much hotter than 120C. Flood cooling and light cuts help, but commercial productivity is low whenever Carbon Steel tooling is used. Manufacturing was revolutionised by HSS because it remains hard up to red-heat temperatures, and carbide has even better heat performance.

For amateur use speed doesn't matter as much. Carbon steel can be made sharper than HSS, which in turn is sharper than carbide. And for many purposes sharpness may be more desirable than cutting speed.

Dave

Edited By SillyOldDuffer on 28/11/2016 11:45:22

Fifty or sixty years ago British carbon steel taps and dies were very good,at work (instrument making) most of the BA and brass thread taps/ dies were carbon steel and in brass ,cast iron and aluminium they would tap hundreds of holes without trouble,we never did much production tapping in steel. I can understand in toolmaking where the value of the workpiece is very high ,the use of ground thread HSS taps and dies being justified due to the tough toolmaking steels and the risk of expensive scrap, though HSS tools in those day were very expensive. Initially I bought carbon taps for model making and they were good ,since then I have acquired a lot of used HSS tooling from tool dealers,boot sales auto jumbles,job lots at auctions,modern carbon taps and dies are definitely not as good ,poorly made,tending to jam in the holes etc though a lot cheaper particularly if a tap is only required for a one off,which happens when working on vintage restoration. If making new models why not use metric, just because a drawing says tap 5 BA use some judgement and use 3mm,and similar with other sizes ,metric HSS tooling is readily available and no doubt cheaper.I can never understand how some so called experienced persons ever come up with the BA system,silly rounded threads with odd angle and ridiculous pitches.

There is no reason why a carbon steel tap should not be made to the highest quality but as it is relatively cheap compared to HSS the cheap end of the market will use carbon steel and has earned carbon steel a reputation for poor quality. The problem is that some poor quality taps are made of HSS so it is not a guarantee of quality. So we are down to choosing brand names of known quality or buying from a reliable supplier of imported Asian equipment. A reputable supplier will stand by his product and take some care in the selection of his stock. The cheapest is seldom the best but some of the major brands offer a performance that far exceeds what most hobbyists need, I feel there is a middle ground of a well made tool at an affordable price. Generally the major brands will not disappoint but they can hit the pocket hard. I have some good quality sets of carbon steel but if I need to replace any I choose HSS so this gives me the usefulness of having the right size but my most used sizes get upgraded to HSS ground thread taps.

Mike

The cost of BA taps is likely to be more than for standard metric – but not hugely so. On the other hand, supplies of BA screws are likely to be twice the price or more, and harder to find. In my UK experience.

Cheers, Tim

I have found over the years that you have to try a lot harder to break a good quality HSS tap off in the job than a similar quality carbon steel. But the cost factor is significant these days.

Whichever way you decide, pay the money for a good quality brand of taps and dies. The cheap ones, even cheap HSS, can result in horror stories.

I am a firm believer in good quality carbon steel taps. (note the "good quality"!) I find that carbon taps are sharper than HSS. Sure they blunt quicker than HSS, but for the average model engineer that doesn't matter. A different case for industrial full time use.

Tempting fate, I have never snapped a carbon steel tap, although I have plenty of broken HSS taps. At least the latter can be ground and used as cutting tools. Good carbon steel taps are around half the price of HSS equivalents.

I am told that it is easier to remove a broken carbon steel tap, but never having broken one, this may not be true.

Andrew.