What Is A "regular" 9 Sb Is Capable Off?

A. Fig Lee

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Hello guys,
I have a mini 7x12 (I know, shame, eh?)..
Not very capable machine. Bought some tooling for it.
4 inch chuck with 3 and 4 jaws, some other stuff.
Bought bearings 30206 to improve it.
At this point I may do regular steel 1/2". 1" Diameter causes me trouble to cut it.
I read some stuff on internet how to improve it..

Anyway, I'm thinking - perhaps I should switch to SB?
What is SB capable of? I need various projects.
Yesterday I needed to use thread die and did not have a holder for it.
So, I would do holders with 20 and 30 mm internal diameter.
Some knobs, other stuff.
What biggest diameter can you turn on SB 9 - regular and stainless steel.
It could do stainless, right?
Thank you.
 
https://m.youtube.com/?#/watch?v=85-uYCoBas8. That video may be taking it to extremes but it shows what is possible. I regularly turn diameters up to 2" easily with my 9" sb. Correctly grinding your tools is the biggest thing along with getting your feed and speed set. I've probably made more parts on my 9" sb than any of my other machines.
 
https://m.youtube.com/?#/watch?v=85-uYCoBas8. That video may be taking it to extremes but it shows what is possible. I regularly turn diameters up to 2" easily with my 9" sb. Correctly grinding your tools is the biggest thing along with getting your feed and speed set. I've probably made more parts on my 9" sb than any of my other machines.

Thank you. Not clear though, what kind of material it was. Seems like some steel - shiny.
Not a stainless steel, no?
 
Every machine has limits, you just need to understand why and what they are.

One major figure of merit for lathes (and other machines) is rigidity. The forces of holding and turning the work and applying the cutting tool should not cause deformation of the machine.

However any slop in the dovetail ways or slides or lead-screw backlash automatically means things have room to move and will lead to bad results.

Check the downloads area here in the Southbend folder for a book called "how to run a lathe" one page shows various projects produced on such a lathe.

If you cut 0.5" steel okay but have trouble with 1" dia. for the same cutting depth, then (if the workpiece and centred and not simply too heavy for the lathe) I'd say that the problem is most likely your rotation speed.

For 1" dia. steel you need to cut your rpm's in half compared to the 0.5 inch steel.
It is really about surface feet per minute(sfpm).
To get your cutting speed:

1) choose a sfpm based on the tool type (HSS or carbide) and the material to be cut.
2) choose the rpm based on the sfpm and diameter of the work.

The sfpm should come from a good reference book, or a reliable on line source.

For example; for cutting regular steel with a high-speed steel tool I typically use 80 sfpm.

For a 0.5" diameter work piece that means about 600 rpm.
However for a 1" diameter work piece it means about 300 rpm.
Those two speed/diameter combinations give the same sfpm!

Experience will tell you if you need to go a little faster or slower.
Since it's a hobby for me, I have never been concerned with cycle times.

-brino
 
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I have been using 9" south bends since I was in trade school in 1981. Technically you can turn a 9" diameter, but to be reasonable, I would say you can turn steel from 4-5" in diameter at a very good rate so long as the machine is in decent shape. I have turned 7" diameter iron on mine numerous times. The longest part was about 16" long and 3.5" in diameter. I have cut S-7, D-2, H-13, knack 55, vicount 44, A-2, P-20 and numerous other steels, aluminum, brass and so on with no problem. I use both carbide, brazed and inserts along with HSS for cutting.
These machines thread exceptionally well. I even broach splines and such on my machine.

These machines are in no way comparable to any of the 7" or 8" Taiwan or Chinese built machines, they are superior in every way.
If you go to buy one make sure the machine is an A model with the quick change box and then make sure the bed and headstock is in good shape.
 
I have a 10K which is a jacked up 9". I have turned 10" parts but 4" is the norm in my shop. Plus everything else you can imagine including milling...Bob

tool bit2.jpg
 
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