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
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
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.
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