86mm KILO 12G “lite” motor – graphite nozzle

Need a good reason to thoroughly clean your lathe? Try machining some graphite. A good shop vacuum cleaner such as a wet /dry Karcher helped a lot in keeping the mess to a minimum. However it showed over time that it was unavoidable that, after machining a full graphite nozzle, the entire lathe was covered in graphite particles.

I had to cut the outer diameter of the nozzle to 79,60mm for easy inserting into the casing. The casing end I had in mind for the nozzle had a small mystery “ding” to it. Average inner diameter of the casing was 79,85mm but a minimum ID reading was as small as 79,70mm and the nozzle with the designed 79,7mm didn’t fit. Being a bit carefull with the fragile graphite I opted for a 79,6mm OD. I also sanded away the inside of the small “ding” as it was less than a 0,15mm. The entire nozzle (of a fairly simple design) took me about 4 hours of machining.

The o-ring grooves came out at 70,7mm for the secondary o-ring groove and 70,8mm for the primary o-ring groove. Where the design called for a 70,9mm o-ring groove which served us well with the previous KILO motors.  It will help inserting the nozzle but I hope it will hold up to 100bar. Even at the second try for the o-ring groove I didn’t get it right. It was difficult getting to the correct depth as the dull tool didn’t cut the final graphite cut but pushed the work piece. Mental note for myself: for the next graphite nozzle keep in mind below tips 1-3.

Drilling the center hole was easy, center drilled, 8mm drill through all, a 18mm drill through all and finishing to 20mm was accurately done with a boring tool.

Tool wear on the carbide inserts was limited and both the parallel turning  / facing insert as well as the boring insert became dull  (for machining metal) but it was not required to replace the inserts before finishing. Cutting the o-ring groove with a HSS tool was different and would required 1-2 sharpening sessions on a bench grinder for a single o-ring groove. It was a pain to get an accurate depth o-ring groove as a dull parting tool didn’t cut the graphite but started pushing the workpiece. Also uneven wear on the tool bit caused different depths.


  1. Go back and forth in the groove with a dull parting tool to accurately (and actually) remove the graphite instead of pushing the work piece away.
  2. Re-sharpen to the tool just prior to the last cut, get a diameter reading (leave 0,1-0,2mm left) and remove the final material by going parallel to the work piece for an even finish of the o-ring groove depth.
  3. Take a wet stone in absence of a bench grinder to keep te tool wear even / parallel to the work piece. Better yet, use a carbide insert cutting tool.

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