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.

Tips:

  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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