I agree with all of your recommendations, Jim. And it's reasonable that if
"I do this" works well, then that's definitely the way to go.
Some of the other folks with different machines will need to adopt their own
"I do this" procedures for whatever works best for them.

The parting tool I've been using is 1/8" wide x 1/2" high HSS, the tapered
cross section type. The tool holder I use also holds the blade at an
(upward) angle, but I haven't measured it. I was concerned that a chip
breaker ground into the tip would be too much top/back relief, but it works
well.
The chip breaker might not be the ideal tool profile for power cross feed,
but it's definitely been beneficial for manual cross feed.
The chip breaker tip has worked well for all of my mild steel and aluminum
parting operations up to about 1.5" diameter, and smaller diameters of
stainless steel (just haven't had any need to part/cutoff larger SS yet).
The very slight front relief made a dramatic improvement, completely
eliminating any digging/grabbing in the workpiece. Of course variable
spindle speed makes it easy to find a good relationship between spindle
speed and manual cross feed rate.

For larger diameters, I use the band saw to cut sections, since the cutoff
blade would be extended too far to complete larger diameters, unless the
larger diameter would have an axial hole, then the parting/cutoff blade
would probably work well.
The problem with large diameter stock is that for parting, the tailstock
center should never be use to complete the parting, so the section of large
round stock would need to be short so that the parting groove would be near
the lathe chuck.

Nearly any parting operation will go smoother if the workpiece is to have an
axial hole in it, and the hole is drilled before the parting/cutoff
operation.

The tapered type parting/cutoff blades provide good side clearances, but
it's important to mount the blade as perfectly vertical as it can be. Some
blade holders aren't machined properly to set the blade in the vertical
position, so the operator needs to be aware of this.

I haven't used the T-shaped parting blades, but I've read good comments
about their performance.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Jim Wilkins" wrote in message
...
On Dec 26, 4:48 pm, "Wild_Bill" wrote:
Grooving and parting off require a rigid setup, which you may already
know,
Tim.
Snug everything down except the cross feed, and even the cross feed if
there
is much backlash in the feed threads.

Including the carriage lock.

My Multifix parting holder and Enco bit work pretty well most of the
time. I don't claim to understand exactly why but I'll describe it for
you. If anyone knows better, listen to them instead. I'm almost
totally self-taught and some of this may be simply adapting to the
quirks of my lathe. "I do this..." is my code for YMMV.

The holder slopes the bit 4 degrees for top rake. The front rake is
presently 16 degrees on the bit, or 12 WRT the work. That may be
excessive. I think the minimum is 5.

I hollow-grind the end so a hand-held stone touches only the cutting
edge and the lower heel. With heel contact to guide it, the stone
doesn't rock vertically when I clean up the edge every few minutes in
SS, or weekly in Al. It rounds the end laterally but that doesn't seem
to matter.

The bit protrudes about 9/16" to cut off up to 1" rod in 5C collets.
It definitely works better at half that.

I grind square across, so the bit leaves a tit on the cut-off part.
Grinding the end at a small angle is said to cure this, but with 9/16"
of protrusion the 0.062" x 1/2" bit flexes too much from the side
thrust.

I use a needle oil bottle to slowly feed oil into the slot. The tip
usually rides along the bottom. This is tedious and boring but if I
stop or try brushing the bit often jams within a minute. The belt is
loose enough that I only have to push the cone pulley backwards to
free the bit, back out, then feed very slowly until the ticking stops.

For a repetitive job I soon get the feed figured out and use the auto
crossfeed.

I tighten the toolpost bolt with the cutoff holder pressed against the
end of the spindle or the collet adapter.

Home Depot pipe threading oil works for me on SS, drill rod and
aluminum.

See/hear chatter, slow down a step. I've only used the backgear when
parting 3" steel, a job I had to complete with the bandsaw.

I make delicate things on the end of solid rod stock held in a collet
and often with tailstock support as well.
How deep are the slots?

Jim Wilkins