Spindle at speed using CSS and G33 (Spindle controlled with VFD)

BigJohnT

I just added a quadrature 720 encoder with index to my BP mill. Assuming you have BP knee mill, not to hijack this thread but was hoping to get your gear ratio for the backgears? I failed to count them when the head was apart!
Also, I don't have a vfd hooked up yet (will be a future upgrade) I'm reading in the spindle rpm to the axis gui via pyvcp and have a spindle speed indicator and at speed led. I'd like to add a second speed indicator that shows the scaled rpm when in backgear. Would you have an example of how to display the correct rpm in backgear?

Thanks!

You should start a new thread for this.

I don't use backgear on my BP.

Yes I use a GS2 with the stock BP 1.5hp motor. but one day I want to put a better motor with a toothed belt drive. I tap at 600-900 RPM with the vari-speed at 500 RPM. I also installed the braking resistor so the drive does not stall during reversal. The GS2 is a bit noisy electrically speaking.

JT

tome wrote: We have CSS on and are threading with a G33 on our Emco lathe and we are seeing the spindle decelerating during the cut.

I think it is probably best not to use CSS when threading. Even with spindle-at-speed working properly you will find that you get different lengths of wait before starting the pass.

If possible try to calculate a fixed spindle speed for the threading passes and then re-enable CSS after the threading is completed.

And why use G33 rather than G76?

Thanks Andy, yes we have now fixed the rpm rather than use css. I also re-wired Hal so that spindle at speed is set by the encoder rather than the VFD, that also made CSS much better, but fixed rpm is better still.

The reason for the G33 is that G76 doesn’t fix the retract path, it varies with each successive cut. This caused the tool to bang into the back of the workpiece and break (annoying for a $100 tool!). We have very tight quarters on the internal acme thread we are cutting (about .010”). We wrote our own threading routine which keeps the retraction path constant, right down the center, so we can control tool position inside the hole. G76 seems to be broken to me since it keeps moving further away from the thread tops with each pass. It is fine for external threads, or internal with a big-ass hole and a small-ass tool but not so good for acme or tight quarters...

-Tom