Turning Ceramic Material on a Lathe

Terry G · 2005-02-23T10:27:14+00:00

I have been attempting to turn down the diameter of some small ceramicmagnets. I have been using my regular carbide inserts and have not beenhaving much luck. I am flooding the magnet with water, and my lathe isrunning at its highest rpms. I am only taking off about 1 to 2 thousands ata time and turning my carriage very very slowly. I have successfullymanaged 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, ortwitch with my hand etc....Is there a specific insert designed for turning ceramic, or are there anyspecial techniques that I haven't mentioned? Is there a recommended insertradius for ceramic?On my cnc mill, I designed a simple jig to securely hold the magnet. Usinga diamond coated 3/16" 4 flute end mill spinning at about 8000rpm withcoolant, I am able to machine down the thickness with no problems. I thenuse a ceramic 1/4" drill bit to drill a hole down the center, again with noproblems. But when it comes to turning down the diameter I just can't do itwith the tools I have.Thanks for any info. I am hoping to succeed in this final machiningoperation.

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Tim Williams 21 years ago

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The funny thing about this story is Si3N4 isn't really all that strong - between porcelain and steel for reaction bonded stuff.

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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 @

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Ed Huntress 21 years ago

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

-- Ed Huntress

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Don Foreman 21 years ago

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

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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.

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Terry 21 years ago

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

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Terry 21 years ago

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.

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Ed Huntress 21 years ago

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

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Terry 21 years ago

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.

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Grunty Grogan 21 years ago

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.)

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