I'm nearing the end of a conversion of a Denford Starmill to replace the old spindle with a Chinese 2.2kW (for the ER20 collet size) spindle and controller.
The existing Mach3 conversion that was done before I got the Starmill had a pretty basic parallel BOB with a relay for the spindle and 0-10V speed controller.
Configuring the controller to support FOR and analogue 0-10V, then hooking up the wires appropriately, this seems to work...
At full speed, with M3 configured to support full spindle speed of 24k, the controller displays 240000 rpm. Below 24k input on M3, the spindle speed appears to lag behind the programmed setting - getting worse, the further away from full speed you get. e.g. at a commanded 5000rpm, the controller is showing more like 2500 rpm. I can probably live with this for now - I'm assuming the PWM drive on the BOB is less than perfect and I know I could probably remedy this somehow. But, I'd like to ask if anyone else has seen similar behaviour?
More sinister, and of more interest to me, there's some, what i can only think to describe as wow/flutter, with the commanded speed oscillating around the set point at around 5Hz, so, the sound of the spindle (the frequency) oscillates around the set point. This doesn't appear related to spindle speed (i.e. if I double/triple the spindle speed, the frequency obviously changes, but the speed of the wow effect remains reasonably constant). Observing the controller there's no fixed speed - the spindle speed varies somewhere around the set point. (I should try it at 24k rpm - didn't think to try that until I started typing here). Assuming that this could be electrical noise, or earth loop, and reading the manual, there's the setting PD071 - Analogue filter (factory:20, 0-50), I've tried changing this up to 50 which should make the controller less responsive to changes on the analogue input. This appeared to have no effect. I then slaved a 47uF capacitor between the analogue VI input and ground - there was an immediate dip in the spindle speed which recovered quickly as the capacitor charged up, but the sound remained. Has anyone else observed similar, and found a solution?
(the second part concerns me the most - my brain doesn't like noises that fluctuate like that, and I can't help but think there's likely some stress on the spindle with constant accelerations/decelerations.
These spindles are high speed only and should not be run at less than 8k minimum.John S -
John, thanks for the reply. For clarity, the wow/flutter effect occurs at all speeds less than full - last night I tested the mill by facing a 50x50x80 length of ali at 10,000 rpm, and the sound was very evident - more so when the cutter touched the metal.
Doesn't occur at 24krpm, as an experiment I've ordered some USB/485 converters, will try driving the demanded spindle speed over digital link.
-the power supply /12VDC typically min 300ma/ for the spindle 0-10v, must be separate , do not just take that voltage from somewhere else
-change the trimmer on the output of the board, the one that regulates the 0-10v, or even upgrade it with proper potenciometer
-no need for additional caps if all is working fine. reset back VFD to what it was originally and first do what i suggest above
At the end of the day a crappy BOB does that, i have seen it. So change BOB, or add additional spindle speed controller board /30-40$/
Ahhh, and dont run the spindle at 24k rpm. Or you will shorten its life considerably. In fact never run it more than 18k rpm. And then first run it for a couple of hours at slow speed so grease and bearing sets.
Depending on how you're measuring things, the difference between the electrical frequency and the spindle speed (called slip) could come into play, especially at low speeds. But if the discrepancy is there at no load, it's not that.
If Doddy has a water cooled one, he can run it at lower speeds, just don't expect it be be particularly useful, due to the correspondingly low power.
Last edited by Jonathan; 21-03-2016 at 06:46 PM.
I certainly intend running mine at 24k, its sold as a 24k spindle, my speeds and feeds calcs repeatedly ask for far higher rpm's sometimes up into the 40k's so 24k is pretty mediocre i think.
Yes it's water cooled. My smallest end-mill is 0.2mm dia carbide - yes I'll be at 24k for some things. But not always. Other work would almost certainly be ali., and my test cut was at 10k rpm for an 8mm end-mill.
Now, if only I could get rid of the oscillation on the spindle speed!
Boyan has some reasonably good advice re. PSU, though I'll have to dig out the control box again (behind the compressor, hands-and-knees job) to check out the supply situation - I thought the BOB was on a separate supply.
If the 485 adapter pops through the door before I get to fall to hands-and-knees then I'm tempted with that as a solution (assuming I can get it to work) - the spindle controller is necessarily (physical size, as well as cooling) separate from the control box - removing the analogue side of things is no bad idea.
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