Quote:
Originally Posted by peter_4059
In my experience it depends how deep you cut each pass so I now take 4 or 5 passes to cut these threads trying the fit between each pass as I've also found there is a huge variety in t-threads between different manufacturers. I always run the final cut twice at the same depth setting. I finish off with some very fine wet and dry over the top of the thread to round off the ridges as the cutting tool won't do this.
I'm running the lathe at min RPM (70 I think) when cutting threads.
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Peter I never cut more than 0.2mm for the grunt runs and back down to 0.1mm for the finsh and cleanup runs. As I set my compound at 29 degrees to enable the tool to cut on one face only a cut of 1 mm deep takes about 8 or 9 runs to complete. The threads are clean and sharp this way but the V profile of the cabide tool at 60 deg does not match the rounded thread profile of rolled threads. I have bought a very expensive D Bit grinder which allows the sharpening of drills, mill bits etc etc. It also has attachments that allow precise grinding of both carbide and HSS steel forms for lathe cutting tools as it has a diamond wheel. I intend to produce both internal and external thread cutting tools which deliver the round profile present in many of these metric fine threads used on astro gear. It's not that my threads wont work, I am just one of those painful people who accepts nothing less then perfection in my own workmanship as those who have watched me make the block for my miniture V8 (3" long) have witnessed. I binned 7 attempts (about 50 hours each) before I was finally satisfied with both the accuracy (tolerences) and the finished appearence. I have no problems cutting other pitched threads using the standard tool but the thread form used on astro gear is not standard thus a new tool has to be made. Same if I wanted to cut ACME or ball thread forms, gotta have the right tool for the job.
Sorry Robin I will go away now
Mark