Joseph Gwinn wrote:

My objective is to not break the lathe itself. Â*But blades are
expendable.

Very good! ;-)

The real problem is that when a blade breaks, whatever one is cutting
off is often ruined in the process.

That's part of the learing process. No pain, no gain.

You mean the hold-down plates and the carriage clamp plate.

If the hold-down plates are on the rear, yes. The carriage clamp is on the
front. I mean the similar setup on the rear.
I suspect that your carriage's rear is lifting off. Why?
With a small diameter, the cutting force is projecting within the two guides
of the bed. With a big diameter, the force is moving outside of the guide
and thus tilting your carriage (lifting the rear).


I do use the carriage clamp when cutting off, and it does seat
firmly.

What I do with deep(er) cuts is to initially clamp the carriage and later
(after 1/3 or such) loosen it.
You also have to pay attention that the blade is dead at 90° to the spindle.
An easy way to check this is to move the carriage to the left until the
blade's side touches the chuck's face. No, not with the lathe running G.
Then you see how well it aligns or not.

Ja! Â*But they are pretty big. Â*I'm leaning towards Aloris BXA.

There's one size below size "A". It's "Aa". But you have to check tool
height.
I have similar ones to the Aloris on my small lathe. They aren't good with
repeatability. If you remove it and reinsert it, it is on a slightly
different place.
The Multifix really has an repeatability of 1/100mm. I tried this.


Good. Â*But you will need to watch him try cutoffs before you will be
able to figure out what is wrong.

Will happen when I help him install his VFD. But first, he has to help me
bring down my replacement lathe.
No, I didn't break it! It simply was well out of specs, so I finally got a
new one yesterday.


Nick
--
The lowcost-DRO:
http://www.yadro.de