(12-12-2017, 09:16 PM)f350ca Wrote: .................I tried using a shear tool, my HSS one would wear due to the hardness of the work piece. So I made one by silver brazing a 1 inch square carbide insert into a steel holder. Ground it to a nice sharpe edge on a diamond wheel. Could not for the life of me get it to not chatter at the tailstock end of the 6 inch piece. Would smooth out and cut beautifully at the headstock end.
Greg I've had the same kind of experiences with the shear tool. HSS gets a nice finish but over a length of only a few inches, it wears. Setting up for precise operations, compound turned to 6 degrees (5.7 ideally, LOL), everything snugged down, the shear tool can cut to a tenth.
But it takes a while for that to happen, continually sneaking up on the rough-turned diameter. I found that if I touched off with the spindle stopped, when I started turning, the shear tool was cutting maybe .001 or .002 mils deeper than the rough diameter and that was enough to take the edge off within an inch or two.
This doesn't sound like much of a big deal but as YOU know, this thing has to run at low speeds and fine feeds. Anything that prolongs the process is a PITA ! And to me, the big advantage to this tool is the ability to cut within .0002 - which can happen but apparently not for long, ha-ha.
I also tried carbide - better than HSS but still not what I'd like to see, probably because of the edge of the brazed carbide cutter that I used. When (if ?) I finish my diamond grinder, that was one of the to-do's, to sharpen the edge of a brazed carbide cutter and try the shear configuration again as you did. Given your results, however, sounds like it would be a waste of time.
I wonder if a different cutter arrangement would improve results ... Perhaps a "trailing edge" configuration rather than the "leading edge" that we all have been trying. Maybe brazing an insert on the end of a shank that trails the tool post by an inch or so instead of having the cutting edge at the front of the tool post would produce enough of a different natural resonance to eliminate the chatter ?
I have no sound physical reason to think that this would be better, LOL, just something to try. I would love for the shear tool to perform like those who love it think that it does.
I've read conflicting opinions, the ones that praise the configuration show photos and post accuracy results which I believe but I also read (a while back) a review by a fellow named Carl Darnell IIRC who pointed out the wear and subsequent inaccuracy (I should say taper I suppose) when turning lengths more than an inch or so, which has been my experience.
I hope that, if you come up with a repeatable process, that you'll post it here. You're always on top of this stuff and I suspect that if a practical solution exists, someone like you or Tom will develop it.
Cheers
PS the cylindrical square was a cool and very useful project !