Re: South Bend Model "N" Owners - Resources
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Just 2 minor comments:
Not all threads have a 60 degree angle (the instruction says to set the compund at 30 degrees). That applies only so far as I know to American UN form and ISO metric form. Whitworth form threads are 55 degrees, so set the compound at 27.5 degrees. Acme is 29 degrees, so set to 14.5 degrees, Metric trapezoidal threads (ISO equivalent to Acme) are 30 degrees, so set to 15. You are unlikely to want to screwcut BA threads (47.5 degrees) as all the thread pitches apart from 0BA (1mm pitch) are difficult to achieve as they and the diameters proceed in a geometric progression, not in nice round numbers in anybody's system.
Setting the compound over at half the thread angle applies only to cutting tools that are not manufactured full form carbide inserts. Single purpose full form carbide threading inserts go straight in.
If making a general purpose 55 or 60 degree angle tool for use with feed from the compound slide, only one side will do most or all of the cutting, so the top rake should be a.) suited to the workpiece material and b.) parallel to the direction of feed.
Actually, when cutting ACME or the ISO equivalent, I keep the compound set at 0, so upon achieving the correct measured major & minor diameters and finding the mating thread still tight, I can advance the tool a thour or two at a time longitudinally to widen the groove until it suddenly frees off when tried. I would do the same if I ever had to cut a square thread.
Best wishes to all, and stay healthy,
On Saturday, 25 July 2020, 19:07:12 BST, Louis via groups.io <l_schoolkate@...> wrote:
Everything in your write-up looks fine to me.
I too have a model 'N' but a smaller 9x34 dating to roughly 1933. I've owned mine now for 4 years and it's my go-to lathe for smaller work.
My 9" has a heavier built headstock compared to other 9" South Bends of the same era. The bed is also wider and has the same cross section as my ~1944 Heavy 10. It also has the similar heavy double walled apron and the cross feed and compound both have adjustable tapered gibs. My research indicates that Model 'N's were the more expensive commercial line lathes. During the Great Depression South Bend cut out some of those more expensive features to reduce the cost in some of their other lines.
My 9" sat unused for many decades and shows little wear. Although the controls are slightly different, in practice they work similar to the Heavy 10. Given how overbuilt it is, I expect it will outlive me by many years.
Just for interest's sake, my Heavy 10 is also an unusual model, a Series 'S' benchtop model. It's labelled as a 10L 487Z and has the large bore spindle. However, it has the typical SB rear countershaft not an undermount drive. The lathe is illustrated in the 1941 South Bend catalog on page 41 along with the 487Z catalog number.