G96 Questions

[acrodave]

This may sound funny, but I have had a couple of HL-2's for more than a dozen years, and have never had this question come up.....

What, exactly, is the "calibration" surface speed for the G96 command ....

That may not be the right question, but if I set S4500 (My HL's are the 5000 rpm machines) and "clamp" the speed to 4000 rpm, then what surface speed in (I assume) ft per second would I be getting .....

I run parts which almost all are conical/spherical in nature, and they taper from anywhere between 2 and 6 inches down to "zero"..... been running them for years, but this question just came up in trying to switch to constant RPM in order to eliminate some deceleration problems....

Another question is that using G96 it's easy to set it to restrict the max RPM to a number, but is there any way to set up a MINIMUM RPM??

My problem is that when the turret retracts in X for a tool change, it slows the spindle enough so that it must then accelerate before it can resume cutting... All of these acceleration/deceleration cycles are taking up time, and wasting energy (boy, do those ballast resistors get hot!).

Dave

[dcoupar]

1. Surface speed is in units (feet in inch mode) per minute. I'm not sure I follow your question.

2. As far as I know, there's no equivalent for G50 to set the minimum RPM, but you can program a G97 with a "target" RPM before you retract to the index position.

G01 X-0.03 (LAST CUT FOR THIS TOOL)
G97 S2500 (TARGET RPM FOR NEXT TOOL)
G28 U0 W0 (GO HOME)
M01

N2 (NEXT TOOL)
...
...
G97 S2500 (TARGET RPM FOR THIS TOOL)
G00 X2.6 Z0.1
G96 S1500 (SFM FOR THIS TOOL)

[acrodave]

Dcoupar:

That makes sense, but the manual does not say that in so many words.....

The manual uses very vague language where in one place it says the "S" units are in RPM, and then under G96 is says "The current S code is used to determine the surface speed"

Am I right in assuming that the "S" code (and indicator) becomes SFM when a G96 is invoked, and is in RPM when a G97 is invoked..... same command is interpreted differently depending upon which G code is in effect??

Am I also right in assuming that the "Clamp" speed set with G50 is always in RPM???

That would explain why the "S" indication on the current commands page stays the same while the spindle, obviously, changes in speed.....

It would have been so easy if the manual had simply said.... "With G97 invoked, the "S" command is in RPM. With G96 invoked, the "S" command is is SFM, (or MM per M in metric)."

I guess that would have been too simple.....

Thanks for the answer ........ now I need to use this knowledge to make the machine do what I want it to do.... I think invoking a G97 when doing the tool changes will be my best option, as well as in a couple of other places, and then going back to G96 when it is appropriate.... Seems to me that using G96 when using any G0 move in X is a bad idea, and is, probably causing my problem...... the spindle is struggling to keep up.

Dave

[Geof]

The S value in G96 S500 is the surface feet per minute that the controller maintains .

The S value in G50 S2000 is the maximum spindle revolutions per minute.

Invoke G96 just before you want it and with the tool right at the start point; if you are out further on X the machine will slow down the spindle and waste time.

Similarly as soon as you are finished with CSS invoke G97 so the spindle does not slow down as the machine moves X away ready for a tool change.

[tobyaxis]

To add to what Geof said above, use G96 with parts larger than 1 inch or 25.4mm in diameter. Under 1 inch (25.4mm) the spindle will run at the max set G50S???? RPM.

Also never use G96 for threading, drilling, or tapping.