Neil,

That does seem very surprising;

Three hypotheses [with so supporting evidence]:

1. in a tangential holder, the loads are "along the grain" of the tool
2. the tool clamping may not be good enough … causing chatter/dig-ins
3. a bad batch of HSS

MichaelG.

What material are you cutting? could be a hard spot in a casting or cheap HSS

Neil,

Are all your failures associated with intermittent cuts? Check your overall tool clamping and stiffness as you could see at least twice the cutting load applied at the moment of restarting the intermittent cut and this may flex your whole mounting structure (toolholder , toolpost, topslide etc) If this flex leads to a digging in of the tool you could expect occasional chipping and tool failures.

Not withstanding this, the other suggestions are all relevant,

Bob D

Just to expand on this when I first started using a tangential holder I only gave the front corner if the tool a slight bevel, and often found the sharp point would break off. It's very annoying because you have to grind off a lot of hss to re-form the point. I now round the edge quite a lot and have had no more problems except when taking heavy intermittent cuts. I think it's also useful to run the spindle faster, I've stopped pussy footing with the lathe and find everything works better when you wind up the speed.

This steel was developed by Fredrick Taylor at the Bethlehem Steel work in the US in 1900 and given the designation HSS for High Speed Steel.

Unfortunately the Indians in a cock up of translation designated it HSS Highly Soft Steel.

Sounds like you have the latter.

I think your technique needs investigating before the tool bit is.

Neil, I found out how to chip the end of A HSS tool today, I had a 1" high tensile bolt that required it's heat bought down in diameter, so I deliberately pushed it until I stalled the lathe (belt head), and then backed out, then a little click, and a sliver about a mm wide broke off the tip. The tool was not very sharp to start with, it would have done the job if I had done it properly, but I just wanted to see what would happen. The tool was 1/4" sq. Ian S C

I have some tool bits about 6" long named Deloro 100 and it is hard to grind but tough as old boots when working. Trying to snap a bit off by grinding all round is dangerous and I wrap a cloth around it for safety. Then again I have some 6mm bits for the boring tool that lose their edge in minutes!

Clive