Spindle Oscillating at 8000 RPM and Over

[mflux_gamblej]

i have a 1992 4020 HT

it has a Baldor H2 drive in it tho, prev. owner put it in.

I swapped in a new spindle last year, this is when that trouble started. I also put in a new mag prox sensor at that time. The spindle had many faults without the new prox sensor. however, now the spindle has issues getting up to high RPM. at about 8000 RPM the spindle will oscillate in speed. if you decrease the speed with the override pot, the oscillations stop. If you increase the speed the oscillations get worse, and if you really push it, the spindle will fault out, and coast to a stop.

not sure what to do here.

if you warm up the spindle for a while near 8K, like at 6k for a few minutes, then it will run at 8k just fine. if you let it set a few hours, you have to warm it up again.

its a 10K machine tho - can't run it much harder than 8.

any ideas?

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[rodney247]

How far away from the magnet is the Hall-effect sensor. Should be about the thickness of a six inch scale

[mflux_gamblej]

i can check it sometime soon. the magnet is down inside the pulley a bit, so even if i bottom out the prox sensor to the pulley it would be farther than about 20 thou for sure.

maybe i need a new magnet. i worried that heating the pulley may affect the magnet. not sure..

[rodney247]

The magnet should be flush to the top of the pulley. And i have taken many many pulley's off and it has never hurt the magnet.

[mflux_gamblej]

i have identified the problem by running the diagnostic mode on the baldor H2 drive on this machine. its a bad encoder (or a ditry one)

you can put the drive in V/F mode where it wont even use the encoder. then you can set the motor moving as usual M3 S9000. works a treat, but its open loop control (no rigid tap). i have no oscillations in that mode. while in V/F mode you can go and read the encoder counts anyhow from the diagnostic screens. all is well until you get up above about 8K then the measured RPM fluctuates a LOT like say 1000RPM. thats why there are oscillations because the drive is comping for speed on its control loop. bad encoder.

i'll replace it asap. I have a US Digital encoder sold to me by ITS but my older machine won't hook up to that encoder because the cable is different. wtf. they sold me that a while back and said it would work. guess i gotta get the $$ one to work with my older machine, or buy and or solder up a custom cable to convert it to the cheaper encoder.

anyhow - thought id wrap this one up. seems like a smoking gun using that diag. on the H2 keypad

[mflux_gamblej]

well, i am in the middle of replacing the spindle encoder. thought this was a 10 minute job - of course its not.

kmac sold me a US digital encoder. without the cable i need to hook it up. I bought the cable from them. now I've cut off the old encoder and removed it; what do you know it seems that the shaft on my spindle motor isn't long enough to be able to install the US digital encoder.


i ended up getting a baldor accucoder from a local service tech. F.C. in colorado if any of u know him.. not sure if he wants to be mentioned by name here or not - but thanks!!!!!!!!!

got it up and running, now running H2 drive setup. spindle will go to 10k just fine now, but has some other issues. i hope the drive tune will fix it.

[mflux_gamblej]

fyi if you change from the old accucoder (round body, thin aluminum cap) to the new one which is flat on two sides, looks to be cnc machined aluminum body - the old one is differential and the new one is single ended. so when u go to setup your drive you may need to change a parameter for this.