Saturday, January 12, 2019

A Little Shop Update

I don't know how much interest there is in this subject, but I've entered the refinement phase on the threading-under-CNC project.  Besides, it keeps me off the streets.  In my last post, I mentioned that there was a small chip in the cutter I was using and that I was looking for replacements.  I ended up ordering this set via Amazon, because a larger version was recommended to me on a machinist's forum specifically pointing out the thread cutting insert.

The set comes with six other cutters, including a parting or slotting tool, three general use cutters in different profiles, and a pair of matching left and right cutters in a good general-purpose shape.  (Left and right mean the direction the cutter is intended to be advanced while turning).  I have other cutters that could fill in for everything except this threading cutter. 

It may not be obvious in that view, but the tip of the cutter angles up several degrees (called the  back rake angle - the optimum value depends on the material it's cutting, so any one cutter is a compromise).  The front of the holder is angled away from the work so that the bottom of the holder is farther from the work than the part of the holder that the carbide sits on.  My only issue is that when I ordered this I should have done more research.  The tool makers do make different inserts for intended ranges of thread pitches; for example, you might see one sold for pitches from 8 to 48 Turns per Inch.  I'm not sure what this one should cut, but my guess is it won't cut everything I'll end up needing to cut. 

At the top of the frame is another 10-32 screw, this time cut from 1018 cold-rolled steel; it cut easily, and I'm guessing the tool will be fine for 4-40 up to about 1/2-13.  It may be the same as that 8 to 48 insert.  I need to look at options, whether it's a bigger holder and a little bigger size class cutter than this or some other tool.   I know: it's a surprise that one cutter for a micro lathe won't cut everything imaginable?  Who would have thought? 

Before doing the threading, the 1/4" steel rod blank needed to be prepared and I did that with another of the inserts from this kit.  Worked like a dream. 

CNC lathes can be used for much more than threading, and it's becoming time to try to get it to do other tricks.  Tapers are a natural, and perhaps other shapes generally done with a fixture, like a sphere.  I've done preliminary shaping on the manual lathe, moving that to the CNC lathe, but my goal has been to do it all on one lathe without needing to find part zeroes more than once, so that a piece can get put onto the lathe as piece of bar stock and come out as the part needed for the project I'm working on, or as close as can be done with one lathe.


  1. Boy, do I remember learning to grind tool bits! We spent 3 weeks on it in the Machine Shop class I took in College. The teacher could take a blank, and grind a perfect tool in minutes. The rest of us never got that good!

  2. One day you will evolve into designing shapes that cannot be made by subtractive machining, and you will have to move on out into the wide, wonderful world of additive machining. Heh.

    Nice-looking thread.

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  4. That is one wicked cool little insert!