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Preparing a ceramic tube for a swagelok

Written by Robert Greenyer on .

For those needing to grind/machine the ends of sintered ceramic tubing, Bob Higgins has some advice...

"Here is a photo of machining the end of the alumina tube to 3/8" OD to accept the Swagelok nut and ferrules.  I put a piece of heatshrink tubing loosely around the tube and clamped it gently in the 3-jaw chuck in my lathe.  For a turning tool, I mounted a Dremel tool on the tool-post and in the Dremel was a diamond drum that was 1/4" diameter and 0.5" long like this one from eBay:

Diamond cutter

I made cuts ~0.0005" (12.5 microns) in each pass and cut 0.7" from the end of the tube.  The cutting was done dry with the lathe and Dremel tool turning in opposite directions.  Cutting slowly did not generate much heat and the diamond drum worked fine for all 3 tubes I machined (no indication that it became worn out)."

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0 #3 AlanG 2015-07-20 16:35
One detail I found necessary if a Swagelok pass-through is used, as for a core thermocouple or electrode. The ceramic tubes are made by extrusion and the inner and outer diameters are not perfectly concentric as manufactured.

The grinding process offers an opportunity to correct this. Using a live center tool when machining the end of the tube will make the ground outer surface concentric with the bore. The Swagelok pass-through hole will then line up with the bore so that the thermocouple sheath or electrode doesn't bind.
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0 #2 Alan Smith 2015-07-19 10:16
Good information - many thanks. I have done quite a bit of machining using diamond tooling on both glass and ceramics, but always using water-flushed cutting surfaces. My main comment is to be very careful about the dust thrown off during dry machining materials like this. Aluminium oxide is a potentially serious lung irritant with long term consequences for health. Doing this a few times ordinary care and dust masks is probably enough, but I would prefer to use a fresh-air face mask and clean up the area afterward with a damp or oily cloth that gets binned afterwards.
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0 #1 Ecco 2015-07-19 10:00
Coincidentally, a few days ago I tried searching the net for information on machining alumina ceramic tubes. Turns out it's not an easy task to do at all. Diamond bits are a must and the job should be preferably done with plenty of cooling and high lathe speeds.

I guess it must be easier if one only needs to grind the surface a bit, though.
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