Turning Ceramic Material on a Lathe
 

I have been attempting to turn down the diameter of some small ceramic
magnets. I have been using my regular carbide inserts and have not been
having much luck. I am flooding the magnet with water, and my lathe is
running at its highest rpms. I am only taking off about 1 to 2 thousands at
a time and turning my carriage very very slowly. I have successfully
managed to turn down 2 magnets so far, but have failed at about 8.
Basically, the magnets just crumble if I accidentally take off to much, or
twitch with my hand etc....

Is there a specific insert designed for turning ceramic, or are there any
special techniques that I haven't mentioned? Is there a recommended insert
radius for ceramic?

On my cnc mill, I designed a simple jig to securely hold the magnet. Using
a diamond coated 3/16" 4 flute end mill spinning at about 8000rpm with
coolant, I am able to machine down the thickness with no problems. I then
use a ceramic 1/4" drill bit to drill a hole down the center, again with no
problems. But when it comes to turning down the diameter I just can't do it
with the tools I have.

Thanks for any info. I am hoping to succeed in this final machining
operation.

"Terry G" wrote in message
news:6UYSd.80843$Yu.64019@fed1read01...
I have been attempting to turn down the diameter of some small ceramic
magnets. I have been using my regular carbide inserts and have not been
having much luck. I am flooding the magnet with water, and my lathe is
running at its highest rpms. I am only taking off about 1 to 2 thousands
at
a time and turning my carriage very very slowly. I have successfully
managed to turn down 2 magnets so far, but have failed at about 8.
Basically, the magnets just crumble if I accidentally take off to much, or
twitch with my hand etc....

Is there a specific insert designed for turning ceramic, or are there any
special techniques that I haven't mentioned? Is there a recommended
insert
radius for ceramic?

On my cnc mill, I designed a simple jig to securely hold the magnet.
Using
a diamond coated 3/16" 4 flute end mill spinning at about 8000rpm with
coolant, I am able to machine down the thickness with no problems. I then
use a ceramic 1/4" drill bit to drill a hole down the center, again with
no
problems. But when it comes to turning down the diameter I just can't do
it
with the tools I have.

Thanks for any info. I am hoping to succeed in this final machining
operation.




You probably answered your own question. Unless you have a "machinable"
ceramic like Macor or lava you'll need diamond tooling. I believe diamond
tipped inserts are available.
Randy

The company we purchase them from can machine them, but the lead times
are very long and we just can't wait. They did say we should use
diamond tooling, but I have not seen any diamond coated turning
inserts. I will have to look a bit more.

Thanks

"Terry" wrote in message
ps.com...
The company we purchase them from can machine them, but the lead times
are very long and we just can't wait. They did say we should use
diamond tooling, but I have not seen any diamond coated turning
inserts. I will have to look a bit more.

Look them up on Google. They've been around for some years now. I was
writing articles about them back in the '90s.

--
Ed Huntress

How about some diamond coated (or similar) sand paper mounted to the
back of one of my turning tools. The magnet is only 2mm thick.

Not sure what grit would be best though. Maybe a 220 or 400? Then I
could flood that with water, and change it frequently. Just a thought.

Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

Thanks

"Terry" wrote in message
oups.com...
Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

Got a toolpost grinder? Carbide or diamond grit burr/stone?

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

On Wed, 23 Feb 2005 12:48:54 -0500, "Ed Huntress"
wrote:

"Terry" wrote in message
ups.com...
The company we purchase them from can machine them, but the lead times
are very long and we just can't wait. They did say we should use
diamond tooling, but I have not seen any diamond coated turning
inserts. I will have to look a bit more.

Look them up on Google. They've been around for some years now. I was
writing articles about them back in the '90s.

Search term "PCD Inserts"

Gunner

Rule #35
"That which does not kill you,
has made a huge tactical error"

Terry wrote:

How about some diamond coated (or similar) sand paper mounted to the
back of one of my turning tools. The magnet is only 2mm thick.

Not sure what grit would be best though. Maybe a 220 or 400? Then I
could flood that with water, and change it frequently. Just a thought.

Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

In spite of the fact that I don't know what I'm talking about, the
phrase "tool post grinder" keeps bubbling up to the top of my head --
the sandpaper will just make a set of grooves unless it's moving.

McMaster has diamond-tipped lathe bits, page 2370.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Terry" wrote in message
oups.com...
How about some diamond coated (or similar) sand paper mounted to the
back of one of my turning tools. The magnet is only 2mm thick.

I don't know of any such sandpaper (it may be around, I've just not heard of
it), but how much material do you have to remove?


Not sure what grit would be best though. Maybe a 220 or 400? Then I
could flood that with water, and change it frequently. Just a thought.

Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

First, that kind of unusual-but-practical information is not something I
would know from experience. My way of finding out such things is to look it
up or to go directly to the experts and ask them. This is 'way outside of my
knowledge.

Second, if you have to remove 2.5 mm of hard material, I think the sandpaper
idea will become a career g, but you'd better get some other opinions.

Third, although I have no specific info, here are a couple of general ideas.
Sintered ceramics usually are ground, not single-point turned. When they
machine engineering ceramics in production it's usually done with green
(unsintered) ceramics, or with glassy ceramics that are made to be machined
(Macor, for example).

I don't know anything about the machining properties of magnet ceramics. In
general, again, you turn or mill friable materials with the smallest cutting
edge and the slightest feedrate you can -- a sharp tool, in other words.

But ceramics vary widely in their properties, and this is one you could only
learn from experience, unless you trip across someone else's account of how
it's done -- from experience.

Good luck. Probably it's doable, somehow. I just don't know where to send
you for information, beyond the makers of the material itself.

--
Ed Huntress

"Gunner" wrote in message
...
On Wed, 23 Feb 2005 12:48:54 -0500, "Ed Huntress"
wrote:

"Terry" wrote in message
ups.com...
The company we purchase them from can machine them, but the lead times
are very long and we just can't wait. They did say we should use
diamond tooling, but I have not seen any diamond coated turning
inserts. I will have to look a bit more.

Look them up on Google. They've been around for some years now. I was
writing articles about them back in the '90s.

Search term "PCD Inserts"

Gunner

This isn't PCD inserts he's looking for, however. It's vapor-deposited
diamond coatings. They're a lot cheaper and a bit harder...although they're
also a lot thinner.

Maybe they'll appear in a search for PCD but that isn't where I'd start.

--
Ed Huntress

"Terry" wrote in message
oups.com...
How about some diamond coated (or similar) sand paper mounted to the
back of one of my turning tools. The magnet is only 2mm thick.

Not sure what grit would be best though. Maybe a 220 or 400? Then I
could flood that with water, and change it frequently. Just a thought.

Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

Thanks

Whoops, I should point out something else: The powder that will get in the
air from either grinding or turning (amount unknown) could turn out to be
VERY nasty, even highly toxic, stuff. You'd better do some checking. A lot
of exotic materials that are harmless as solid pieces turn into
skull-and-crossbones stuff when they're turned into fine particulates.

--
Ed Huntress

On Wed, 23 Feb 2005 02:27:14 -0800, "Terry G"
wrote:

I have been attempting to turn down the diameter of some small ceramic
magnets. I have been using my regular carbide inserts and have not been
having much luck. I am flooding the magnet with water, and my lathe is
running at its highest rpms. I am only taking off about 1 to 2 thousands at
a time and turning my carriage very very slowly. I have successfully
managed to turn down 2 magnets so far, but have failed at about 8.
Basically, the magnets just crumble if I accidentally take off to much, or
twitch with my hand etc....

Is there a specific insert designed for turning ceramic, or are there any
special techniques that I haven't mentioned? Is there a recommended insert
radius for ceramic?

On my cnc mill, I designed a simple jig to securely hold the magnet. Using
a diamond coated 3/16" 4 flute end mill spinning at about 8000rpm with
coolant, I am able to machine down the thickness with no problems. I then
use a ceramic 1/4" drill bit to drill a hole down the center, again with no
problems. But when it comes to turning down the diameter I just can't do it
with the tools I have.

Thanks for any info. I am hoping to succeed in this final machining
operation.

Ferrites are usually ground wet with diamond wheels. It's messy, but
a diamond wheel can remove quite a bit of ferrite in a fairly short
time.

Don, you mentioned using a diamond wheel. What would I use on my
lathe to turn down the diameter? From experience so far, a sharp point
turning insert does not work very well. Maybe I should try one of my
larger radius inserts.

Do they have any type of diamond impregnated abrasive material I can
use on a lathe? I am just throwing things out right now. I don't
really know what else to try.

I will look at the McMaster diamond tips tools. But the magnets or so
fragile, that if the tip of the tool catches any tiny imperfection, the
magnet breaks.

Thanks for all the info.

"Terry" wrote in message
oups.com...
How about some diamond coated (or similar) sand paper mounted to the
back of one of my turning tools. The magnet is only 2mm thick.

Not sure what grit would be best though. Maybe a 220 or 400? Then I
could flood that with water, and change it frequently. Just a thought.

Ed: What radius insert would you recommend for turning a ceramic
magnet that is 2mm thick. I am going from 12.5mm dia. down to 10mm
dia.

Thanks


Ceramic is much like glass. A hard brittle substance. I would grind it with
a diamond wheel on a flexible shaft. Terry is on the right track. But, a
wheel will be much faster.

Please note: I'm not a machinist, but I do know glass.

Randy Hansen
SC Glass Tech.
Scam Diego, Comi-fornia

But ceramics vary widely in their properties, and this is one you could
only
learn from experience, unless you trip across someone else's account of how
it's done -- from experience.


When I worked for Dow they brought in a ceramic they wanted me to try and
drill with the ultrasonic drill we used on glass. After 2 days drilling and
wearing out 4 bits I was able to make a 3/16" wide dent about 1/8" deep in
it.

This stuff had a Rockwell rating of 97 for hardness!

Randy Hansen
SC Glass Tech.
Scam Diego, Comi-fornia

"Ed Huntress" wrote in message
...
Whoops, I should point out something else: The powder that will get in the
air from either grinding or turning (amount unknown) could turn out to be
VERY nasty, even highly toxic, stuff.

It's my experience that magnets really like to stick together. I haven't
ground any so can't say if the average grinder would throw the dust hard
enough though.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"Randy H." wrote in message
news:VtcTd.117917$0u.32003@fed1read04...
But ceramics vary widely in their properties, and this is one you could
only
learn from experience, unless you trip across someone else's account of
how
it's done -- from experience.


When I worked for Dow they brought in a ceramic they wanted me to try and
drill with the ultrasonic drill we used on glass. After 2 days drilling
and
wearing out 4 bits I was able to make a 3/16" wide dent about 1/8" deep in
it.

This stuff had a Rockwell rating of 97 for hardness!

Some of the engineering ceramics are unbelievable.

Back when GE had a division working on making injection-molded,
silicon-nitride turbocharger turbines (around 1980), they sent us editors a
sample of the material, which was a stick around 4" long, 1/4" wide, and a
little more than 3/16" thick. Silicon nitride is as hard as the hammers of
hell and I expected it to be brittle. So I closed the door to my office,
propped the stick up against the bottom of the door at a 45-deg. angle, and
stomped on it with the heel of my shoe.

It dug a 1/2" gouge in my door. But it didn't break the first time. I really
had to hit it very hard before it broke.

--
Ed Huntress

"Tim Williams" wrote in message
...
"Ed Huntress" wrote in message
...
Whoops, I should point out something else: The powder that will get in
the
air from either grinding or turning (amount unknown) could turn out to be
VERY nasty, even highly toxic, stuff.

It's my experience that magnets really like to stick together. I haven't
ground any so can't say if the average grinder would throw the dust hard
enough though.

Tim

from http://www.wondermagnet.com/magfaq.html

Can I cut, drill or machine magnets to my own sizes and shapes?

Yes and no. AlNiCo magnets are very easy to machine in any way you wish.
NdFeB magnets are by nature very hard and brittle. Although they can be cut,
drilled and machined, it should ONLY be done by folks who are experienced
with ceramics. If the magnets get over about 300 deg F, they will lose their
magnetism permanently. They are flammable, and it is not difficult while
grinding or machining to get them (or the chips and dusts from cutting) so
hot hot they ignite. If they do ignite, the fumes are toxic and the material
burns very fast and hot, like Magnesium! In our experience any machining of
these magnets should be done with diamond tools under lots of coolant with
good ventilation and the risk of fire in mind.

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

I purchased the diamond tip turning bit from McMaster that Tim found.
I will be here today. I'll give it another try. I am using lots of
coolant. The tool and magnet never even get warm. As far as the dust.
I would imagine the magnet would keep it down, as long as the coolant.
But I will be more cautious of it.

Randy, not quite sure how I would use a diamond griding wheel on my
lathe to turn down the diameter. I need to be accurate to a couple of
thousands.

I tried machining some of those AlNiCo magnets last week. I think they
were the AlNiCo 8 ones which had around 5% cobalt in them. That was a
challenge. I wore out a solid cobalt drill bit, which barely put a
dent in the magnet and a 3/16" solid carbide endmill which rounded the
corners off only after a coulpe of passes.

As most can probably tell by now, I am pretty new to machining these
things. But I am sure learning alot!

Thanks.

"Terry" wrote in message
oups.com...
I purchased the diamond tip turning bit from McMaster that Tim found.
I will be here today. I'll give it another try. I am using lots of
coolant. The tool and magnet never even get warm. As far as the dust.
I would imagine the magnet would keep it down, as long as the coolant.
But I will be more cautious of it.

Randy, not quite sure how I would use a diamond griding wheel on my
lathe to turn down the diameter. I need to be accurate to a couple of
thousands.

I tried machining some of those AlNiCo magnets last week. I think they
were the AlNiCo 8 ones which had around 5% cobalt in them. That was a
challenge. I wore out a solid cobalt drill bit, which barely put a
dent in the magnet and a 3/16" solid carbide endmill which rounded the
corners off only after a coulpe of passes.

As most can probably tell by now, I am pretty new to machining these
things. But I am sure learning alot!

One thing you may now learn is that diamond-coated tools, or those tipped
with a polycrystalline diamond compact, are not usually sharp unless you
specificy that you want them sharp.

Anyhow, let us know how it works.

--
Ed Huntress

On 23 Feb 2005 14:09:50 -0800, "Terry" wrote:

Don, you mentioned using a diamond wheel. What would I use on my
lathe to turn down the diameter? From experience so far, a sharp point
turning insert does not work very well. Maybe I should try one of my
larger radius inserts.

Do they have any type of diamond impregnated abrasive material I can
use on a lathe? I am just throwing things out right now. I don't
really know what else to try.

I will look at the McMaster diamond tips tools. But the magnets or so
fragile, that if the tip of the tool catches any tiny imperfection, the
magnet breaks.

Thanks for all the info.

"Ed Huntress" wrote in message
...
Some of the engineering ceramics are unbelievable.

....
It dug a 1/2" gouge in my door. But it didn't break the first time. I
really
had to hit it very hard before it broke.

The funny thing about this story is Si3N4 isn't really all that strong -
between porcelain and steel for reaction bonded stuff.
http://www.matweb.com/search/Specifi...bassnum=CM0019
Some of the tougher processes, HIP for instance, get up there though.

I don't suppose your sample was monocrystalline?

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"Tim Williams" wrote in message
...
"Ed Huntress" wrote in message
...
Some of the engineering ceramics are unbelievable.

...
It dug a 1/2" gouge in my door. But it didn't break the first time. I
really
had to hit it very hard before it broke.

The funny thing about this story is Si3N4 isn't really all that strong -
between porcelain and steel for reaction bonded stuff.
http://www.matweb.com/search/Specifi...bassnum=CM0019
Some of the tougher processes, HIP for instance, get up there though.

I don't suppose your sample was monocrystalline?

No. Self-sintered. Maybe HIPped, I don't know. Tough as hell.

--
Ed Huntress

On 23 Feb 2005 14:09:50 -0800, "Terry" wrote:

Don, you mentioned using a diamond wheel. What would I use on my
lathe to turn down the diameter? From experience so far, a sharp point
turning insert does not work very well. Maybe I should try one of my
larger radius inserts.

Do they have any type of diamond impregnated abrasive material I can
use on a lathe? I am just throwing things out right now. I don't
really know what else to try.

I would think of it more as a grinding or abrasion operation than as
turning. I don't think I'd do it in a lathe because I wouldn't want
that abrasive mess near it. The little ferrite machining I've done
has been freehand with diamond burrs in a Dremel or diegrinder.

You might use a 1/4" shaft diamond "burr" or even a diamond wheel in
your mill. For wheels, see
http://www.cyberrockhound.com/grinding_wheels.htm
Set up a spin index or rotary table, mount the workpiece to that, and
advance the work toward the spinning burr by moving the mill table.
Rotate the work 360 by hand, advance another coupla thou and do it
again, and so on. If I had a lot of them to do, I might rig up a
slo-syn motor to the crank of the rotary table.

Yes, I read that somewhere. I'll just have to give it a try.

I received the diamond tip turning tool yesterday, and it worked great.
I was able to turn down the diameter of a couple of magnets with a
perfect finish and no chipping.

Thanks for all the suggestions and help.

"Terry" wrote in message
oups.com...
I received the diamond tip turning tool yesterday, and it worked great.
I was able to turn down the diameter of a couple of magnets with a
perfect finish and no chipping.

Thanks for all the suggestions and help.

I'm glad that worked out for you, Terry. Unless the ceramic gives the
diamond a major workout, it should last you a long time. I have one I found
7 or 8 years ago, unused and lying in a trash can (no kidding), that I pull
out when I have to turn fiberglass and carbon-fiber composites, mostly
ferrule pieces for flyrods. It's great for that and it shows no signs of
wear, even under high magnification. At this rate, it will last the rest of
my life.

--
Ed Huntress

Another question regarding the ceramic magnets. I have always assumed
that you want to machine ceramic with the cutter running at a high
speed, and lots of water. I am turning a 3/16" diamond coated end mill
at around 8000rpm and taking off .005 at a feedrate of 1ipm. I then do
a .001 finish pass. I get a nice finish, and haven't really broken any
during this operation, but I do get some edges that I can see and feel
with my nail. Would changing my rpm or feedrate take care of this?

Also, on the lathe, should I be spinning the workpiece at maximum rpms?
I am only taking off about 1 to 2 thousands and moving the carraige
very slow.

And finally, when I am drilling with a 1/4" ceramic bit, I am spinning
at around 4000rpm. It is working ok for me, but I have exploded a
couple of magnets doing this. I think that might be kind of fast.
When drilling ceramic is it typical to spin the bit at a much lower
rpm? I will also be using an 1/8" bit on some magnets this weekend.

I don't really have the magnets to experiment with, so I am sticking
with what is sort of working for me.

Any suggestions or guide lines I may not be following that will keep
my magnet scraps down?

Thanks.

On Wed, 23 Feb 2005 02:27:14 -0800, "Terry G"
wrote:

I have been attempting to turn down the diameter of some small ceramic
magnets. I have been using my regular carbide inserts and have not been
having much luck.

You will use a diamond post grinder. Single point diamond turning will
be too slow for that diameter reduction and will still chip the
material.
But the good new is that a foredom handpiece will fit many Phase II
boring bar holders, and sintered bronze or even plated type diamond
shank-mounted wheels are cheap and available a lot of places.
You will not be able to observe the surface while you are machining
(wet) because the magnet itself will hold the particles, so will be
coated with black gunk.
(I once worked at an optics company. We routinely edged exotic
materials to round blanks: Sapphire, various ceramics and
glass/ceramics, etc.)