Cannot obtain max spindle speed

[Chas]

Hi, just working on getting the spindle running correctly under Oak but have run into a slight problem. i set up the spindle as per instructions to give 10V at max requested rpm of 3000 and when measured all is correct. When an MDI command of 3000 is input the spindle rpm display reads 1500 which is verified with an optical tacho. This must be because there is a 2:1 pulley ratio between the motor and spindle (the 5000 count hollow shaft encoder is mounted directly on the spindle). I then changed parameter 33 to a value of 2 which then corrects the display and actual rpm to that which was requested. i.e. a request for 750 rpm now gives a reading of 750 and an actual rotational speed of 750 rpm. All good. Now the problem, a request for 750 rpm now reads at 5V instead of 2.5V which it did before so i cannot get the spindle to rotate faster than 1500rpm which is now at a reading of a full 10V whereas it should be at 5V. Is there another parameter i need to change to get back to a 5V output at 1500 rpm to enable me to achieve 3000 rpm at 10V.
Reports when parameter 33 set to 1 and 2.
Thanks
Chas

[tblough]

Set the Oak up for 3000 max rpm and verify that you have 10V at the analog out WITHOUT the VFD connected. If correct, connect your VFD and verify you still have 10V.

Parameter 33 should be left at 1 unless you are using multiple gear ratios like high/low range on a Bridgeport.

If the Oak is outputting 10V when 3000rpm is commanded, then the Oak is configured correctly and you will need to adjust your VFD settings until the spindle speed is 3000rpm. This is usually some Max Hz setting and is probably set to 60Hz and will need to be changed higher to increase the top speed of the motor.

[Chas]

Hi Tom, thanks for that. You were quite correct in that i did not have the max frequency set high enough in the inverter. I've set parameter 33 back to 1 and it seems okay now. The only fault i now have is that once the rpm display readout gets above around 1200 rpm the readout starts to become very erratic. I am using a Yumo 5000 count hollow shaft encoder. Do you think this is likely to be where the problem lies. They are supposed to be good up to 5000 rpm and i'm nowhere near that. I've checked the actual rpm and it's rock solid.

[tblough]

If you have a 5000 line encoder with 20,000 pulses per rev, you could be exceeding the bandwidth of the Oak encoder port. Centroid recommends a 1000 line encoder (4000 ppr) for spindles.

I have two mills with 1000 line spindle encoders and both are solid at 5000 rpm.

[martyscncgarage]

Keith did a nice write up on tuning and setting up VFD/Spindle speed:
viewtopic.php?f=63&t=1650

[Chas]

Thanks all, Tom looks like you were right re the 5000 count encoder. I have a 1024 count version of the same encoder so I swapped it out for that one and the readout is correct and completely stable at higher rpm. Just need to work out why the VFD switches itself off as the spindle approaches 1750 rpm but that’s probably a question for the VFD manufacturers.
Many thanks
Chas