Subject: machining ceramics

From: [email-masked] (VAntonova)
Date: 13 Dec 1996 00:25:45 GMT

For a high-power tube radio transmitter I need to machine some material
with very high electrical resistance, minimum heat resistance and that can
withstand temperatures up to 600-1000 degrees F. I decided that the stuff
used in the tubes which I am making the transmitter out of is the best,
which is some sort of ceramic very similar to the clay used in clay pots.
I decided to take a broken pot from the basement and try to mill it, with
the obvious problem of chipping aand extreme dulling of the cutter. I need
a fairly precise cut for maximum heat transfer. I guess diamond bits will
work, but I haven't seen any for sale, and I think they are very
expensive. The other option is to make a  rough cut and braze the ceramic
to the metal, which is aluminum plated copper.Is this possible or should I
just give up? Thanks for any info.

Alex.

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From: [email-masked] ("Richard Sewell")
Date: Fri, 13 Dec 1996 16:58:33 GMT

> withstand temperatures up to 600-1000 degrees F. 

I've seen 'machinable ceramics' for sale - at frightening prices, but I 
think they're what you want. Alternatively, would it be possible to make 
the right shape out of wet porcelain & fire it ?

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From: [email-masked] (Jonathan M. Elson)
Date: 13 Dec 1996 05:49:24 GMT

VAntonova ([email-masked]) wrote:
: For a high-power tube radio transmitter I need to machine some material
: with very high electrical resistance, minimum heat resistance and that can
: withstand temperatures up to 600-1000 degrees F. I decided that the stuff
: used in the tubes which I am making the transmitter out of is the best,
: which is some sort of ceramic very similar to the clay used in clay pots.
: I decided to take a broken pot from the basement and try to mill it, with
: the obvious problem of chipping aand extreme dulling of the cutter. I need
: a fairly precise cut for maximum heat transfer. I guess diamond bits will
: work, but I haven't seen any for sale, and I think they are very
: expensive. The other option is to make a  rough cut and braze the ceramic
: to the metal, which is aluminum plated copper.Is this possible or should I
: just give up? Thanks for any info.

Warning!  The ceramic used in high power transmitting tubes is often
Zirconia, (or Beryllia) which are highly toxic!  The dust is easily
absorbed in the lungs!  Don't even think of grinding these materials.
This ceramic is most likely VERY DIFFERENT from what is in clay pots!
Beryllia (Beryllium Oxide) is the best ceramic heat conductor, far better
than most metals (ie. Copper and Aluminum).  It also makes a great
insulator.

I don't think you will have any luck getting brazing to stick to ceramic.
Diamond wheels will cut these and other ceramics quite well.  the trick
is to keep the wheel and workpiece cooled with a mist (or dribble) of
water.  I ground vee grooves in glass for a friend's project using a
thin diamond resin-bonded disc.  Once we got the trick to apply water
in the correct way, it went very well and quickly, with minimal chipping.
The diamond wheel was absolutely untouched by the grinding work.

Whether the cuts are rough or smooth, for best heat transfer, a heat
transfer medium which fills the voids and unevenness between the two
surfaces must be used.  At low temperatures, zinc oxide in silicone oil
is used (heat sink grease).  There should be a special version of this
for higher temperatures.  If the cut surface is not smooth, it can be
lapped smooth with a flat plate and carbide sandpaper.  Lay the sandpaper
face up on the flat plate, wet it, and rub the surface to be smoothed
across the sandpaper.  Start with a coarse sandpaper, and follow with
finer grades.  This goes much faster than you might imagine, as long as
the sandpaper grit is harder than the work material.

					Jon

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From: [email-masked] (Jens)
Date: Thu, 12 Dec 1996 07:06:47 -0800

>withstand temperatures up to 600-1000 degrees F.

How about machineable ceramics ????

Jens

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From: [email-masked]
Date: 13 Dec 1996 16:40:29 GMT

>just give up? Thanks for any info.

Why not make them out of clay and have them fired? Check for local pottery
clubs. The temperature range you need to withstand doesn't sound too high
for some readily available ceramic clays.

Peter

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From: [email-masked] (JD)
Date: Fri, 13 Dec 96 14:45:40 GMT

>just give up? Thanks for any info.

The easiest way to machine ceramic is with a laser. Depending on what
your budget is for getting this done, it may be feasable if you require
great accuracy. (from my experience, most laser houses have about a
$100 minimum, not bad for getting it done perfect.) IF your interested,
I can e-mail you the names of a couple real good laser guys.

---

From: [email-masked] (michael jensen)
Date: 13 Dec 1996 20:08:57 GMT

VAntonova ([email-masked]) wrote:
: For a high-power tube radio transmitter I need to machine some material
: with very high electrical resistance, minimum heat resistance and that can
: withstand temperatures up to 600-1000 degrees F.

     Try Macor a machinable glass ceramic.  You can purchase macor out
of the McMaster-Carr catalog.  The big plus to Macor is that it can be
machined with High Speed or Carbide tool.  It is also possible to hold
a very very tight tolerance +/- .0001 inches depending on the 
acccuracy of your machine tools.  The negatives to macor are, it 
brittle and doesn't have a very high tensile strength. If you use it 
in a high stress application it will fail.

     Good Luck

     Mike J.
--
Mike Jensen ([email-masked]) 
Chemistry Instrument Shop              
University of Nebraska - Lincoln
(402) 472-3542

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From: [email-masked] (Reckless)
Date: Sat, 14 Dec 1996 06:37:11 GMT

>Alex.

I doubt the heat conducting capability (thermal resistance) of clay
pot material is good enough to keep the tubes cool.  Most of the
high-power tube sockets that I have seen are porcelain, and if I'm not
mistaken it is denser and conducts heat better.

I would expect that a well-planned mold could be used with wet
porcelain to form the socket which would then require only minimal
machine work.  

Another possible source might be the ceramic plates that hybrid IC's
and multi-chip-modules are made on.  Those are already quite flat and
smooth and MCM panels are as large as 4" square and maybe .100" thick.
These usually use ceramic for heat dissipation reasons, so the
material may be the type you need.

Hope this helps
-Reckless

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From: [email-masked] (Boris Beizer)
Date: Sat, 14 Dec 1996 08:58:48

In article <[email-masked]> Richard Sewell wrote:
>Date:	Fri, 13 Dec 1996 16:58:33 GMT
>From:	[email-masked] ("Richard Sewell")
>Newsgroups:	rec.crafts.metalworking
>Subject:	Re: machining ceramics

>the right shape out of wet porcelain & fire it ?

Possible, but don't forget the unpredictable shrinkage of ceramics when
they are fired--about 15% - 25%.  Also distortion is to be expected.  If
you have to make a tubular item (I assume that's what you want) don't
expect to get the right ID and OD and length without a lot of experimentation.
I learned this from observing my mud-slinger (pottery potterer) wife.
    As for machining, expect very high breakage (e.g., 90%).  The 
breakage starts when you first try to chuck the piece up.  I have tried
this without notable success.  As for tool bits, carbides at least, possibly
diamond.  Here's a possible suggestion: I haven't tried it this way. 

1.  Play around with the rough piece until you get the fired piece oversized
    slightly for ID, OD, and length. 

2.  Use some kind of epoxy putty to make a collar for chucking.  While it is 
    still soft, mount it in the chuck and indicate it to center it.  

3.  Don't try cutting tools.  Use a tool post grinder or mount a dremel
    tool with an appropriate stone.  I have tried that and inevitably, I
    shatter the piece.  

4.  Use very slow rotation (slowest) very low feeds, very shallow cuts.

5.  Protect all metal parts of the lathe in sight with cloth to prevent your
    lathe from getting ruined by the huge amount of destructive grit this 
    will throw up.

6.  Lubricate with lots of water.

Alternatively:
    See if you can buy some used Klystrons from a radio or TV station.
    Butchering may be easier than machining. 

Good luck-- you'll need it.

Boris

---------------------------------------------------------------------------------------------------------
Boris Beizer, PhD                                 Consulting and Seminars on
1232 Glenbrook Road                          Software Testing and
Huntingdon Valley, PA 19006              Quality Assurance
TEL:  215-572-5580
FAX:  215-886-0144
Email: [email-masked]
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From: [email-masked](Dale A. Keltie )
Date: 14 Dec 1996 20:09:16 GMT

In <[email-masked]> [email-masked]
(VAntonova) writes: 
>
>For a high-power tube radio transmitter I need to machine some
material with very high electrical resistance, minimum heat resistance
and that can withstand temperatures up to 600-1000 degrees F.
<snip>

Alex -

You might want to check out a material called 'Macor', a machinable
ceramic manufactured by Corning.  Continuous operating temp. close to
1500 deg. (F).  It's expensive to be sure; a 1" dia. x 3" long piece of
the stuff is about $55.00 for example.  

Wesgo/Duramic has the stuff ($100.00 min. order)
26 Madison Rd.
Fairfield, NJ 07004
Tel: 201-227-8877
Fax: 201-227-7135

Regards,
Dale

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From: Rick Cook <[email-masked]>
Date: 16 Dec 1996 02:44:44 GMT

JD wrote:
> The other option is to make a  rough cut and braze the ceramic

In all seriousness, the best place to ask for information on 'machining'
ceramics is over in the hobby group devoted to rockhounds and lapidary.
This stuff is best worked with equipment like the stuff used to cut and
shape semiprecious and precious materials.

There's an entire technology base there and it can be used to do some
fairly precise work.

--RC

--RC

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From: Rick Cook <[email-masked]>
Date: 16 Dec 1996 02:44:54 GMT

michael jensen wrote:
> The negatives to macor are, it 
How is this stuff on heat transfer and electrical resistance? I understand
that's what he's looking for.

--RC

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From: Rick Cook <[email-masked]>
Date: 16 Dec 1996 02:44:39 GMT

>the right shape out of wet porcelain & fire it ?
Hmm. Contact the Norton Corp. in the Boston area. They're makers of
abrasives and ceramics and they're experts at this kind of problem. They
also make diamond films that might be the best way to do what you want.

--RC

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From: Steve Hardy <[email-masked]>
Date: Mon, 16 Dec 1996 02:41:21 GMT

> in a high stress application it will fail.

Yes, Macor.  Only $3000 per Kg from Crown Scientific in Australia.
Does McMaster-Carr have it for a more down-to-earth price and if
so how can I contact them?

After all, this stuff is basically mica in a borosilicate glass
matrix.  I would have expected the price to be about as much as
brass, but nooooo - it just _had_ to be totally unafordable.
It is used on the space shuttle.  Anything which goes into space
seems to attract a 10000% 'Pentagon' premium.

Regards,
SJH
Canberra, Australia

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From: [email-masked] (michael jensen)
Date: 16 Dec 1996 14:01:49 GMT

Steve Hardy ([email-masked]) wrote:
: michael jensen wrote:
: > 
: > VAntonova ([email-masked]) wrote:
: > : For a high-power tube radio transmitter I need to machine some material
: > : with very high electrical resistance, minimum heat resistance and that can
: > : withstand temperatures up to 600-1000 degrees F.
: > 
: >      Try Macor a machinable glass ceramic.  You can purchase macor out
: > of the McMaster-Carr catalog.  The big plus to Macor is that it can be
: > machined with High Speed or Carbide tool.  It is also possible to hold
: > a very very tight tolerance +/- .0001 inches depending on the
: > acccuracy of your machine tools.  The negatives to macor are, it
: > brittle and doesn't have a very high tensile strength. If you use it
: > in a high stress application it will fail.
: > 
: >      Good Luck
: > 
: >      Mike J.

: Yes, Macor.  Only $3000 per Kg from Crown Scientific in Australia.
: Does McMaster-Carr have it for a more down-to-earth price and if
: so how can I contact them?

: After all, this stuff is basically mica in a borosilicate glass
: matrix.  I would have expected the price to be about as much as
: brass, but nooooo - it just _had_ to be totally unafordable.
: It is used on the space shuttle.  Anything which goes into space
: seems to attract a 10000% 'Pentagon' premium.

: Regards,
: SJH
: Canberra, Australia

     If you want high performance you have to pay the price. Generally
material cost are the least of your worrys, but with macor you pay 
a little more for the materials.  For protype work it is much cheap 
and far more accurate to spend the money and buy the right material. 
Even if it cost more then coventional materials, in the long run it is 
cheaper because it is done right the first time.

     Mike J.