Denford Software & Machines

I have a Denford Zerocentre CNC Mill. At the moment if you program a speed of greater than 4000rpm the actual spindle speed drops as the machine assumes that a gear change has taken place.

The only way of changing the drive ratio is to change the position of the drive belt to a different set of pullies.

If I was to permanently change the drive ratio to allow the higher rpm which parameter would require to be altered to allow this change? such that if the machine was programmed at less than 4000 rpm it would run at the correct rpm. I guess that I need to set the speed that it assumes the gear change has taken place to be very low ie 10rpm.

I would also need to confirm that the ratio set in the parameters was correct - Where would this be specified?

Hugh Watson

Innova Design & Build Ltd

Hi,

I'm guessing this is a Fanuc OTA/B
I don't know the machine, but can help with the Fanuc parameters:

Parameters 540,541,542 and 543 correspond to the speeds in gears 1,2,3 and 4.
It depends on the PLC and machine as to how many are used.
If you only have one range then 540 would be set to 4000RPM for 10V analogue output.
If you had two ranges then you might have:
540: 2000
541: 4000
etc...

Hope this helps

Sorry I forgot to mention it is Fanuc OM. would this make a difference?

Hugh

Not for these parameters.

My fault - I thought it was a lathe (OT)

If you look at those parameters and the values make sense, then they are the ones - give it a try - you can't do any harm (famous last words )

If you change the 4000 to say 8000, then all your actual speeds will be halfed as the Fanuc is now outputting half the analogue voltage for the requested speed (eg, 4000 is now 5V 8000 is now 10V)

At the moment the values are
540 4000
541 4000
542 4095
543 0035

Am I right in thinking that if I change 540,541, to 100 and 543 to 6010 then if the program speed is between 100 and 6000 the machine will always think it is its high gear. Or have I missed the point somewhere!

Hugh

If I remember correctly, the Fanuc itself will choose the gear range according to the spindle speed programmed, by setting a gear change
request flag to the PLC logic.
It uses these parameters to decide which gear to pick. The logic will then confirm which gear it has changed to

Because the first three are set to 4000RPM (or thereabouts) I would guess its single speed - the 2nd and 3rd parameters look like they are set to 4000 just in case the PLC logic tells the Fanuc that it is actually in gear 2 or 3.

So, if you want to change the pulleys to get 6000rpm, I would change the parameters to:
540: 6000
541: 6000
542: 6095
543: 0035

On the Zerocentre we never used\set the gear ratio on the spindle pulleys. ONLY PARAMETER 540 WAS SET. It may be that you need to set the speeds up as Andy is saying if you want to use the second ratio.
If you change to the other ratio then I guess you need to set Parameter 540 to the new speed.

I have changed the belt position and change the parameters as you said and it does now appear to run to 6000rpm.

The only problem now is that I don't have any way of confirming the spindle speed as there is no encoder on the spindle. How do I know if Fanuc is using the correct ratios?

Any ideas on a way of checking this?

I did mark the spindle and run at 120 rpm and count the rotations. it did seem very slightly slow, 31-32 secs for 60 rotations. Not very scientific though!

The best way to tell the actual speed is to measure directly from the spindle using a tachometer.

It appears that E-Bay has lots of digital tachometers for around £20.

Good luck.