Hi Terry:
Have you factored in the reality that small insert bars are typically even MORE fragile than small solid carbide ones?
I've had poor success with insert bars in the 1/4" diameter range...everything is so damned tiny that even looking at it cross eyed risks trashing it.
Having said that I've got to say that buying solid carbide ones is awfully pricey and I baulked at going that route too.
So I learned to grind small bars efficiently and now my problems are over.
I can knock up a single point threading bar that's exactly what I need in about a half an hour of quality un-interrupted time on the Deckel and the Cincinnatti style home made cutter grinder.
I have them all dressed up with the accessories I need to whip out a cutter quickly, and I have a Shadowgraph to check it on too.
However, one crucially important caveat...making ONE bar is a doddle; making a BUNCH of identical bars on a manual grinder is one helluva challenge if they have to be consistent within tenths...so all bets are off if you want these for production turning.
If you're doing this a lot as I do, it may well be a worthwhile investment for you too, and it's truly not rocket science; so you can get good at it with just a bit of persistence.
However if you do this kind of work only occasionally, I would just keep buying them from Harvey or wherever, and try, as MattiJ suggests in post #3 to figure out what's going wrong and why they're breaking on you.
I've turned some ridiculously small deep internal threads and I can't remember ever breaking a bar.
The picture shows two kinds of modified 6:32 threads each 0.400 deep and they were single pointed with a custom made bar
I have fucked up a fair few threads though.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com