Gary,
From your description it seems that you are possibly trying to cut a tough stainless steel part with a carbon steel die. I used to work as a sales engineer for a British manufacturer of all types of threading tools & have seen this situation many times when visiting clients to discuss their threading problems.
Taps & dies are essentially manufactured from either carbon (CSCT) or high speed steel (HSSGT). What’s the difference you may ask? Well it’s price for a start. If you look at any tap manufacturers or sellers price list including Tracy Tools & The Tap & Die Company’s you’ll notice in the small print that HSS is available for an additional charge which from memory is at least 150%. For that reason most of us will always opt for Carbon Steel, the cheapest & in most cases more than adequate for our needs.
What are the differences between taps & dies made from the two materials? Firstly the abbreviation CSCT stands for Carbon Steel Cut Thread & it refers to a tap that is to all intents & purposes produced with a single point tool or screwcut just as you would on your lathe. HSSGT is an abbreviation for High Speed Steel Ground Thread & refers to a thread that is produced by grinding using a wheel dressed to the thread form. The materials that are used are different also. Carbon Steel is easier to work & is essentially similar to silver steel & it is hardened & tempered after machining similar to how we do it in our workshops. HSSGT though is another matter; it hardens & is tempered at much higher temperatures & difficult to do in the home workshop! HSSGT taps are ground from a finished ground & fluted blank, the thread form is the last feature to be produced. CSCT dies are produced with a tap, HSSGT dies are thread form ground, just like a tap but obviously internally ground rather than external. There is still more to it though.
What your 150% premium for a HSSGT tap also buys is a tap or die produced to tighter tolerances & it is thus capable of producing internal threads to tighter tolerances. CSCT taps are also made by reputable manufacturers to a tolerance but the tolerance band is much wider. Dies are also produced to a tolerance but because a split die is slightly adjustable the physical size of the thread produced can vary. With a solid die however the die is manufactured to a different tolerance. In all cases taps & dies from reputable manufacturers will have the tolerance band stamped, engraved or etched onto the shank of the tap or the face of the die. I can no longer recall what the tolerance bands are unfortunately.
How does all that I have written apply to your problem you may well ask? Hopper has summed it up very well in that you probably need to us HSSGT, but unfortunately HSSGT may not be the solution in itself. Tapping & threading lubricants have part to play in the process & help to improve the quality of the cut thread in most cases.
The Tap & Die Company have been around for many years. As they say on the website, since 1978.
I Hope that the above is of interest to you & to others who have possibly wondered about the difference between cheap & expensive threading tools. There’s more to them than meets the eye at first glance.
Alan