Cheap milling machine spindle - BT30-ER20, air powered draw bar + Tear Down!

For reasons that will soon become apparent I was searching for a milling machine spindle and came across this interesting item. BT30-ER20 tool holder, air powered draw bar for tool changing, HTD5 belt drive drive and ready to accept your choice of motor. Seemed too cheap to be true so naturally I had to buy one and find out . . .


https://youtu.be/pBomasw4Ow0

Next part I'm looking into is a servo to drive the head of this planned DIY milling machine.

Requirements are:
Milling head is ~40kg
Driven by 5mm ballscrews
Running on 20mm linear rails
Total head travel is about 350mm and I'd like to cover this in 5 seconds max under rapids
Pulley ratio 3:1

This AC servo seems OK:
https://www.omc-stepperonline.com/a6...-rs750h2b1-m17
Attachment 32714

750W
integrated brake
2.39Nm torque, 8Nm peak
Mains powered servo driver
Accepts pulse step/direction (I'll be running it from an ESP32 microprocessor since it does lots of other things as well)

I need to use this for drilling as well by moving the head down. My calculations show the axial force from the servo and ballscrew is 1607N peak, along with some of the mass of the head backdriving the ballscrew so this seems OK to me.

Does anyone have any experience with these AC servos, and any comments on the above requirements?
They also do an ethernet version (more money) but I don't know if I can interface to that from my microcontroller so am looking at the usual step/direction pulse control. I'll probably need electronic gearing too.

Thanks

I decided to strip down the rear end of this spindle to get access to the pulley. It took longer than expected!


https://youtu.be/p8kE8pJgYn8

Quote:

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Originally Posted by routercnc

Does anyone have any experience with these AC servos, and any comments on the above requirements?
They also do an ethernet version (more money) but I don't know if I can interface to that from my microcontroller so am looking at the usual step/direction pulse control. I'll probably need electronic gearing too.

Thanks

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I think I fitted a similar drive for someone last year.
They're all a much of a muchness. I suspect there's limited actual manufacturers of the drives, and they're mostly relabelled/cloned.


Biggest pain is wiring up the connectors, then deciphering the manual to find the correct settings that you need.

Thanks m_c. From what I can tell they should be more than powerful enough for what I need. I've seen them used on a 150kg bridgeport knee (usually via a pulley of 3:1 or similar) so my 40kg head should lift up, and also there should be plenty spare to push the quill/head down for drilling.

I was concerned about the fiddly wiring/soldering but I see they do sell a ready made breakout connector with the big plug on one end (around £10 I think) and labelled/crimped terminals on the other for all the ins and outs, and it comes with the motor and encoder connectors ready to plug in. I did look into Ethernet control as that would be very neat and some versions of the servo drive have that but then I would need to get into TCP, masks, addresses and so on. There did seem to be some ethernet adapters for the ESP32 microcontroller which might do something but I think in the end I've decided to stick with step/direction control which means going back to the big breakout connector.

I'm used to those 'special' manuals by now so hopefully with that, chat GPT and forums I can get it to do what I want. I do plan to read out the AB (and maybe Z) channels of the servo encoder from the drive into the ESP32 to get it synchronised with the main spindle encoder for rigid tapping, just for the challenge.

Suitable BOBs do make life far easier, especially with the micro sub-d connectors used.

The 'Ethernet' control is more likely to be EtherCAT, CAN, or ModBus.

ModBus is generally too slow for typical CNC use. Even at high baud rates, you're looking at multiple millisecond refresh times for a single drive, which gets compounded when you add more drives.
CAN works at varying speeds, with continual data packets between all devices, and quite a lot of microcontrollers have it as an option.
EtherCAT typically uses a fixed 1kHz refresh rate (slower and faster optiosn exist, but 1kHz is the usual), with data frames passed through each slave (aka drive) with each drive extracting and adding it's own information.

I've got a set of EtherCAT closed loop steppers, as I really like the idea of it due to simple wiring (just standard CAT cables between drives) and each drive lets you add inputs/outputs, but the LinuxCNC implementation is buggy, and I'm not invested in it quite enough to use any of the Mach compatible controllers.
I might dust of a RPi and see if any of the bugs have been ironed out of the LinuxCNC implementation some time though, although I might just sell the drives to free up some shelf space.

Thanks that’s good info. I think I’m going with step/dir version just waiting for them to be back in stock (in the UK) otherwise import and shipping double the price.

I decided to get this upgrade done and out of the way so I could move onto the next part of the project . .


https://youtu.be/tDka6cVuDqE

If anyone is interested I've uploaded my CAD for the original version of this spindle onto GrabCAD:
https://grabcad.com/library/bt30-non...mbly-5000rpm-1

Let me know if anyone is interested in the floating cylinder version that I made and I'll export the files to GrabCAD.

Time to get this project started . . .

https://youtu.be/ioo_Vyz_lmk