Aloris Parting Tools - I don't understand...

[Bob Korves]

Actually, a rear mounted parting tool pushes down on the cross slide/ways and increases rigidity. It is a vastly superior way to part on a lathe.

Only if it is mounted cutting edge up, spindle running in reverse (clockwise) direction. The standard cutoff arrangement also pushes down on the cross slide/carriage.

 

[mikey]

I've used one for about 15+ years or so and am familiar with how it works. A rear mounted parting tool is mounted upside down and the lathe turns in the normal direction. As the tool enters the work the cutting forces push the tip of the tool up. Since the tool is somewhat rigidly mounted to the tool post and the tool post is locked down on the cross slide/compound, the forces will push down on the cross slide and increase rigidity. There are numerous advantages to this arrangement, the increase in ridigity being only one.

Edit: we have had this discussion several times before and lots of guys have trouble visualizing how the forces are distributed. A front-mounted parting tool lifts the cross slide up and reduces rigidity; a rear mounted tool does the opposite. Many small lathes that have difficulty parting from the front can part without issue when the tool is mounted in the rear because of this. My little Sherline will part almost anything I can mount on it at quite high speeds (1200+ rpm in mild steel and stainless, 1800 rpm in aluminum, etc) with a P1-N blade (only 0.040" thick) when parting from the rear but from the front, it chatters.

A similar thing happens when you mount a parting tool upside down and part from the front, with the lathe running in reverse. It works.

 

[ddickey]

It works great. Although I will admit I have never parted with a tradition parting tool. Only the FoR from Eccentric Engineering.
Bought a few blades here. https://www.sommatool.com/