Evan¡ what am I missing. If the tool is upside down behind the work, normal rotation would be called for¡ right?
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David Robertson
YES DAVID you are correct. ?You use normal rotation with a rear tool upside down! ?I got that wrong.
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An alternative is to use the parting tool in the normal tool post, upside down. In that case you run the motor backwards. It may be difficult to adjust the height of the cutting point. ?And problems with screw-on chucks getting unscrewed. I see Arthur Coe just posted that too.
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And the backwards single point threading also requires the motor to run backwards with the tool upside down in the normal tool post. That way you cut away from the shoulder and don't have to stop threading abruptly. This is useful when you cannot disengage the half-nuts eg when cutting a metric thread on an imperial lathe or vice versa.
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Evan
Lathe: 1955 Boxford Model A with screw cutting gearbox, power feed with several accessories, hand tools and a pillar drill press.
Try my Free Online Gear train Software:
You enter a thread pitch or TPI and it shows you a range of gear trains and gearbox setting to use and even a scale drawing of the gear train.
It also includes calculations for taper turning by the tailstock offset method, and cutting speeds.
It includes the specifications for many thread types eg metric, UNC, BSW, and BA.
Displays drill sizes for tapping threads at any percent thread depth (with full explanations).
My YouTube Channel and Playlist about using an engineers lathe: ?
Project to build a Greek Hero steam engine and measure its power output:?
Evan