Machinable Ceramics

[Anonymous]

Hi all,

 

Has anybody had experience of turning the machinable ceramics? In the UK Macor seems to be the most common trade name. The professionals don’t seem that enamoured with it:

 

http://www.practicalmachinist.com/vb/cnc-machining/turning-macor-machinable-ceramic-206494/ 

 

I was planning to design and make my own spark plug for my hit ‘n’ miss engine, and this seemed like a good opportunity to try machining ceramics. Ever since the stuff first appeared in the RS catalogue years ago I’ve been looking for a reason to use it. However, the stuff is expensive, and if it’s going to be a PITA to machine I might just buy a spark plug instead. It’s not like I’m short of projects!

 

Regards,

 

Andrew

[Anonymous]

[KWILParticipant @kwil]

Yes, some time ago I was involved in using machinable ceramics to make the stator and rotor for a specialist type of rotary switch. The ceramic was machined in the “green” state and then placed in a kiln to complete the firing process. The result was good, repeatable and very strong. We turned, drilled and milled slots. I do not recall the product name though.

[BazParticipant @baz89810]

I machine quite a lot of ceramic in my day job, you will need decent carbide tips, use plenty of coolant and you should be OK

[Sam StonesParticipant @samstones42903]

Didn’t someone once write an article in ME using Araldite for the insulation?

 

It would have been in the 70’s when I read it.

 

Sam

[Pete JonesParticipant @petejones68962]

Hi Andrew,
I was also looking at using Macor for plug insulators – very expensive stuff! Then I read somewhere that Corian (kitchen worktop material – 1/3 acrylic polymer, 2/3 aluminium trihydrate) was also a good insulator material unless you’re making plugs for a high performance engine – clearly not a problem on a hit-and-miss. I managed to get half a dozen 2″x5″x1/2″ off-cuts from an eBay trader (apparently, it’s a popular handle material with knife makers) for a fiver and set about making some M5 plugs for my 2cc 4-stroke. It’s quite easy to machine with ordinary HSS tools but it does wear the sharp edge off quite quickly so regular stonings are required. Had a few mishaps along the way – too heavy a cut with a worn tool – which would have been very costly in Macor!
Have (hopefully) attached some photos of the finished article. It’s been run for about an hour now at up to 11,400 rpm and seems to be holding up well.
Best regards,

Pete

 

[Lawrie Alush-JaggsParticipant @lawriealush-jaggs50843]

Geez some people on this site amaze me!  I never tire of seeing the ingenuity, inventiveness and quality of workmanship.

[Ian S CParticipant @iansc]

I seem to remember sparkplugs made by melting the little peice of glass tube found inside a 230V incandesant light bulb into the metal plug body with the electrode through the hole, and one of those little ceramic insulator beads on top. It was in ME some years ago. Ian S C 

[Anonymous]

Hi Pete,

 

Thank you for the information and sorry for being slow in replying. I’ve been on holiday up north (down south to our esteemed editor) with the glider.

 

Brilliant idea to use Corian, I’ll buy a bit from Ebay and give it a try. I had also thought about using a high temperature plastic, such as PEEK1000. Machines well and is good for 250°C. The only doubt I have is how well it will stand up to the flame front temperatures.

 

Time to stop thinking about it and get on and experiment!

 

Regards,

 

Andrew

[Clive HartlandParticipant @clivehartland94829]

Have you ever considered using Mica as an insulator, I remember in my youth seeing spak plugs with mica insulators on old farm engines.

Another thing to try might be fire clay, I expect its still available and it would conform with any ‘locking in’ shape you use. They use it on gas hobs to hold the Piezo igniters in place.

Corien, I have a sheet about 12″ x 12″ which I am willing to donate to the worthy cause of spark plug advancement.

I can cut it into small pieces if needed. All I would need is an address.

 

Clive

[jomacParticipant @jomac]

Peter Hi. The knurling on the prop drivers looks very neat, So how did you do it ???, knurl or machine with a pointed milling bit, the rest of the engine and spark plugs look excellent, So are Ramons engines. I built a Bolaero 18, of the modelenginenews plans, look OK, although I did a few small mods to it, I will, when I learn how to upload photo’s I show you what it looks like, Iv’e not started it yet, but lots of compression, Why not started it !!!, well first up, hard to get cheap fuel, and after all the rain we had, I had to lop some trees and cut down others, ( Im’e getting too old for this caper).

John Holloway

[Richard MarksParticipant @richardmarks80868]

Gentlemen

Having aquired a pulse jet I found that the insulator on the spark plug was badly chipped, the plug is composed of 5 pieces, 2 parts are the main body 1 ceramic insulator and a 2mm central condutor and screw on cap, being a model engineer doesn’t mean I have loads of money but I have an enquiring mind (something my school teachers regarded as a nuisance in my day), anyway back in my early days as a TV engineer we used 10 watt wirewound resistors which have a ceramic body, I just happened to find one with a 2mm hole right through the middle, I made a 2mm mandrel to hold it place between the chuck and the rotating centre and turned down the outside to 4mm using a dremmel mounted on the topslde with a diamond grinding wheel going at slow speed and using the leadscrew and 5thou cuts, the reason I did it this way was because the last one I made got crushed in the chuck because it was so fragile at that size. I did think about alternative materials but as the body of a pulse jet gets a bit hot I thought ceramic should be ok, and yes I know pulse jets are banned but all I will do with this one is run it up for a few seconds for the hell of it and then flog it.

ps Diamond bit sets from Arc Euro Trade, indispensable in my book, no connection but a satisfied customer.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Most common and useful engineering ceramic is trade name STEATITE . Lots of suppliers and lots on the web . Heres a start :

Steatite

| Magnesium Silicate | Advanced Ceramic Materials

Find out more about the ceramic properties of Steatite and how it is produced.
Steatite is a form of Magnesium Silicate and can be used in many applications
…

http://www.morgantechnicalceramics.com

[Ian S CParticipant @iansc]

There was a bit in ME about model spark plugs with Teflon insulator. Ian S C

[Pete JonesParticipant @petejones68962]

Hi John, Thanks.

The ‘knurl’ was machined on my Boxford shaper using a small rotary table tilted at a carefully calculated angle and a 90° vee shaped lathe tool. A bit of a faff but I like the result.

Here’s a link to a short wobbly video of the engine running.

Sorry gents for straying off-topic..!

Pete

 

[Alton OakenParticipant @altonoaken45027]

In electrical and electronic parts, ceramic is done on elements such as insulators, igniters, connectors, seals and magnets etc. For high precision ceramics multi-axis machining is done. Nowadays CNC milling machines and diamond grinders are used fr better machining.

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ceramic machining

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