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Al2O3 is a hard, white material used for making firebricks and numerous molded ceramic parts.

Say I had a firebrick, took a core out of it using a thick-walled diamond hole saw and a drill press.

What lathe insert material would I then use to machine the outside of the Al2O3 cylinder assuming I could take care of all the holes using diamond hole saws?

My budget for one cutting bit would be $500. But that would take me many hours of work to raise, so I prefer something less expensive, since I'm probably going to break it, hence cost effective.

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    $\begingroup$ Is there a reason you can't form the alumina as a cylinder from the start? Machining a brittle, ceramic sample will possibly just end up fracturing the sample. Presumably you are performing some test on the cylinder, or some such? $\endgroup$ – wwarriner Mar 16 '16 at 1:32
  • $\begingroup$ @starrise I'm prototyping on a budget. Custom ceramic shapes are expensive. If it can be molded and that's more cost effective for large quantities then that's what I'll do when I get to that point. Also, I was able to drill out a tube with only a few chips on the ends using $1 hole saws and a wobbly drill press. So this method should work. $\endgroup$ – Shine On You Crazy Diamond Mar 16 '16 at 4:19
  • $\begingroup$ There are a lot of off the shelf ceramic tubes available in various sizes for applications like furnace lining. If these are unsuitable there is also a huge range of castable and rammable refractories available and making a mould for a cylinder should be pretty easy. Another approach is to make a cylinder from ceramic wool and paint it with refractory slip to harden it. Try looking for 'kiln props' form a ceramics supplier. $\endgroup$ – Chris Johns Mar 16 '16 at 19:42
  • $\begingroup$ @ChrisJohns No can do. I need the heat tolerance/properties of professionally made Al2O3. I need custom size tubes of dimensions I don't know exactly yet, and which will change probably every day I work on the project. Machining ceramic works! I just need to know the best bit, thanks. $\endgroup$ – Shine On You Crazy Diamond Mar 16 '16 at 20:28
  • $\begingroup$ I'm not sure what you mean by 'professionally made' kiln props are cylindrica firebricks and castable refractories are designed for exactly this sort of application so I'm not sure why you don't like these options which seem to be ready made solutions to your stated problem. $\endgroup$ – Chris Johns Mar 18 '16 at 0:03
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In industrial applications probably the closest approximation is in dressing bonded abrasive wheels. These use abrasive particles including aluminum oxide but a different bonding medium which makes them a bit tougher than standard fire bricks. With this is mind a diamond tipped dressing tool would probably be a good thing to try.

I lathe turning stone scrapers are widely used. In this case a tough, abrasion resistant tool steel would probably be the best bet perhaps something like D2.

Similarly for turning it is probably well worth sawing the outside to a hex shape to get the section closer to round before you start.

Another approach would be to use a belt linisher with a coarse ceramic belt and a cylindrical grinding jig.

Of course if you just want a simple cylinder it would be logical to use core drills for both the inside and outside. In this case you might want to pre drill a pilot hole in the centre and fit a metal sleeve and use a plain pin instead of the pilot drill in the arbour.

Another big consideration is dust extraction to protect both the machine tool and your lungs a firebrick dust will wreak havoc on both.

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  • $\begingroup$ I was just going to drill press some cores out I can get about 7 cores per brick to experiment on and I have 4 bricks. Then do any fine drilling on the lathe. Thank you for all the tips! $\endgroup$ – Shine On You Crazy Diamond Mar 21 '16 at 0:26
  • $\begingroup$ So I should cover some parts of the lathe in plastic if I get ceramic mud on them? (Was thinking of using a spray bottle). $\endgroup$ – Shine On You Crazy Diamond Mar 21 '16 at 0:30
  • $\begingroup$ Where can you find diamond tipped tools? $\endgroup$ – Shine On You Crazy Diamond Mar 21 '16 at 0:32
  • $\begingroup$ Look for a 'diamond grinding wheel dresser'. $\endgroup$ – Chris Johns Mar 21 '16 at 12:20

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