# Thread: Constant surface speed control

1. ## Constant surface speed control

Hi there!

I've been trying to find some good examples of how does the constant surface speed control work - in numbers (S,F). Couldn't find anything that would be satisfactory.
I've taken some figures from a SECO catalog and applied the G50 code for lathes. I imagined i have to work a piece from a D1=120 mm to a D2=60mm.
In the catalog the Vc=630m/min for a mild steel. The S1 is apx.1340 Rpm and the S2 is apx. 3340 Rpm (for the 60 mm). The Ap=1 to 5 mm. Now, I 'm not certain, but, if the max. Speed, S2, is 3340 Rpm then the Speed I put on the line of G50 is higher?

2. This is correct for a Haas running in Haas or Fanuc mode but I think it is the same for most machines.

For Constant Surface Speed you use S to set the surface feet per minute in the G96 command;

G96 S630000 (on my machine it is in mm)

You do not need to worry about setting the minimum rpm but you can clamp the maximum rpm using a G50 command;

G50 S3400

3. So how arbitrary is the maximum speed that we choose when we use a G50 command? (Except the case when the machine can't go any higher.)

4. The maximum speed you choose depends mostly on the size of your part. For something small you may be able to let the machine run up to its maximum. But if you have a large diameter and the jaws on the chuck are out a long way you might want to set a speed well below the maximum because the centrifugal force tends to open the jaws.

5. What about interior turning using G96? Does the spindle rpm go from a c alculated value (higher) to a lower value?

6. Does not matter, the control keeps the surface speed at the programmed value for the position of the tool tip.