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Another question for everybody. And for this question I need to
clarify that I'm NOT a machining wiz - in fact I don't even have my
own lathe yet.

If a lathe is converted to CNC, I thought that it would make
machining complex tapers and rounds or spheres much easier. But as I
looked at the current manual devices that cut these shapes - say the
spherical ends - the cutter rotates with the device. Which seems to
make sense because then your cutters' angles are always 'correct' in
respect to the tangency of your cut surface.

For a CNC lathe, how do you go about cutting a spherical end without
changing tool bits?

If this is a stupid question, I do apologize.

-Chris

Rotating tool bits? That's a new one on me at the moment. I can see the
sense behind it but I've not seen one that can actually do that available to
the hobbyist. My CNC lathe cuts spheres and tapers with the tool constantly
in the same position.

If you image the stock spinning around, you start the program so the tool
starts the same radius size away from the work as you want to create. It
runs through the program jogging the tool inwards bit by bit until
eventually it just starts to touch the end of radius (The furtherest part
in). From there it carries on jogging in fraction by fraction expanding the
cut it's taking until eventually it's making cuts right across the full
radius you want to turn. The cutting action all takes place on the point of
the tool, maybe a tiny bit to the side of the point sometimes but never
enough to cause a problem.

I don't know how well I've explained that but what I'm trying to say is that
the machine starts miles off from the work and moves in _slowly_ forming the
sphere from the most _extreme_ points first. In the end the tool can pass
the full length of it taking a normal depth of cut. So at the beginning you
have something that looks nothing like what you want. It'll look like a
piece of stock with a bump on the end. After a little while longer the bump
will have a noticable curve. That'll end up as a nice smooth radius. I have
to say here that the steppers on my lathe make a noise like Terminator
himself when they cut a radius, it sounds soooo funky as they cross over!

Tapers are easy and just done in a similar way. You only have a problem when
an angle is created that's steeper than the angle on the point of the tool,
but that's quite unlikely to happen. And even then you can always turn the
toolpost and run it as a seperate program away from the rest at the end.

Regards,
John H.

Another question for everybody. And for this question I need to
clarify that I'm NOT a machining wiz - in fact I don't even have my
own lathe yet.

If a lathe is converted to CNC, I thought that it would make
machining complex tapers and rounds or spheres much easier. But as I
looked at the current manual devices that cut these shapes - say the
spherical ends - the cutter rotates with the device. Which seems to
make sense because then your cutters' angles are always 'correct' in
respect to the tangency of your cut surface.

For a CNC lathe, how do you go about cutting a spherical end without
changing tool bits?

If this is a stupid question, I do apologize.

-Chris


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--- In CAD_CAM_EDM_DRO@y..., "John" <johnhe-uk@s...> wrote:

Rotating tool bits? That's a new one on me at the moment. I can see

the

sense behind it but I've not seen one that can actually do that

available to

the hobbyist. My CNC lathe cuts spheres and tapers with the tool

constantly

in the same position.

Sorry - I should have referred to why I thought this was the case. I
found this on another machining group:


ool.pdf

In his design, the tool is rotated on a yoke. Its a relatively
simple concept actually so I figured that all radius/sphere turning
tools were like this. You can see in his document that he is making
som sphere tipped shafts. So, suppose that you want to cut a shaft
that tapers down toward the end and then at the end you have a
spherical end and not just a half sphere but more like 75% of a
sphere (like what is shown in the above document). Now, your tool
bit has to be able to cut on both sides if you were to do this
without changing the setup. So what kind of tool would you use if
the tool isn't rotating - a cutoff blade? What I find interesting is
that the fundamental approach may have to be different if using CNC
versus manual. Of course, I may be off my proverbial rocker, too.

-Chris

For a CNC lathe, how do you go about cutting a spherical end without
changing tool bits?

A tool with a round insert on it works fine.

As with most things in the real world, it just isn't critical that the tool
be perfectly oriented for every cut. On a manual lathe you are always
confronted with a cutting operation that requires another tool, but are too
lazy to change and you just cut it with the other tool instead. Boring
tools used to take a facing cut after you finish the hole is an example.

Daniel J. Statman, Statman Designs
www.statmandesigns.com
dan.statman@...

--- In CAD_CAM_EDM_DRO@y..., "Chris and Dee" <brunoblazer@y...> wrote:

--- In CAD_CAM_EDM_DRO@y..., "John" <johnhe-uk@s...> wrote:

Rotating tool bits? That's a new one on me at the moment. I can

What I find interesting is

that the fundamental approach may have to be different if using CNC
versus manual. Of course, I may be off my proverbial rocker, too.

-Chris

Hi Chris,
actually if you go check out Guy Lautard's "The Machinist Bedside
Read" you'll find a manual way to turn balls without a special
attachment. The CNC method and the manual method are essential the
same, just a difference of a hardware vs wetware computer. 8^)

BTW, if your new to machining, the Bedside readers are highly
recommended.

Dan Eaton
St. Louis

Chris and Dee wrote:

Another question for everybody. And for this question I need to clarify that I'm NOT a machining wiz - in fact I don't even have my own lathe yet.

If a lathe is converted to CNC, I thought that it would make machining complex tapers and rounds or spheres much easier. But as I looked at the current manual devices that cut these shapes - say the spherical ends - the cutter rotates with the device. Which seems to make sense because then your cutters' angles are always 'correct' in respect to the tangency of your cut surface.

For a CNC lathe, how do you go about cutting a spherical end without changing tool bits?
If this is a stupid question, I do apologize.

You use a circular cutting tool. There is an indexable carbide insert that is round. You can't
cut a complete sphere, as there would be nothing left to hold the part on the chuck. But, if you have
a tool holder that will expose slightly more than 180 degrees of the round insert, you can
do all the external sphere work you could want. Boring most of an internal sphere
would require a holder with a "hook" on the end.

Jon