1.8 KW AC Servo For Spindle Motor

[RJS100]

I recently converted a PM833-TV to cnc. This is a hobby mill. It currently has the stock motor and Durapulse VFD. The mill has an odd design as the motor's base rpm is 1800, but it actually runs at a max of about 7500 rpm with approximately 2:3 to 1 reduction resulting in a max spindle speed of 3200. This means that at max speed it is very loud.

I am planning on using a 1.8KW or 1.5KW AC servo (Chinese model found on internet; JMC or RATTM, they look very similar). My plan is to keep the existing splined gates pulley on the spindle and find a similar sized one to put on the servo. I have seen a number of posts on this forum as well as Youtube with hobbyists doing the same with decent results.

I am not really interested in doing rigid tapping, so my main goal is:
-Control the speed with the analog 0-10V output from Acorn
-Use the relays that are currently connected to the VFD for direction.
-Connect the servo to the E-stop circuit.
-Possibly connect a fault output from the servo drive.

Does anyone have a wiring diagram for this application? I have limited knowledge of these servos and am interested in any feedback I can get regarding tunning or anything else. I noted that some of these have a brake, but I cannot think of why I may need a brake. Links to servos I am considering are noted below.

Best... Richard


Servos:
https://www.ebay.com/itm/265553379296
https://www.ebay.com/itm/194913710100?var=495782291713

[suntravel]

JMC Servo with Acorn:

https://centroidcncforum.com/viewtopic. ... rvo#p67067

Uwe

[RJS100]

Wow. Thanks for such detailed information. What a huge help! Just a few questions:

1. My mill currently has a 2HP induction motor (not a full inverter duty motor). Would you feel comfortable replacing this with a 1.5KW AC servo motor. I was looking for the 2KW JMC servo but have not located it yet. Although the other Chinese servo is readily available with a 1.8KW option, I would prefer to use the JMC as you have done all the detailed work here!

2. Did you use any EMI filters with this drive?
3. I did not see any reference to tuning software. Is this correct?
4. To keep the spindle wires short, my VFD is physically mounted adjacent to the mill head. Do you think this location would work for the AC servo driver?

Thanks again for sharing all your notes... really helpful.

[suntravel]

I use a EMI filter for every servo driver

You can get JMC from Ali or ebay

Do not mount without a cabinet they are not sealed.

Delivery is with 3m cables

Software is attached, but you will need a USB to serial adapter and a serial to USB Micro cable.

Uwe

[RJS100]

Thanks. Did you find much need for the software? I bought cables for some StepperOnline drives and only used once.

[suntravel]

I use the software for backups, copy settings to similar servos and for tuning.
Setting parameters and tuning for speed mode will work without software too.

You need a USB/serial adapter anyway, or maybe you already have one.

I make my own Serial to USB cable with a DB9 plug and an old micro USB cable from a phone.

Uwe

[RJS100]

Thanks. I rec'd a note from an Ebay supplier that the JMC 2.0KW version with a max rpm of 3000 was discontinued quite some time ago. I am leaning towards using the 1.5KW JMC setup as I have limited servo knowledge, and your documentation/notes are a huge help. There is a 1.8 KW AC servo available from another Chinese brand.

I have only machined about a dozen parts on this mill, so my experience is limited here as well. My instincts say that on these benchtop mills, rigidity is the limiting factor. A 1.5KW servo is technically equivalent to the stock 2HP induction motor. Do you think the 1.5KW option would be sufficient? On an expensive full inverter duty 2HP motors, the torque is closer to the 2.0 KW or 1.8 KW AC servo motors.

Best... Richard

[suntravel]

1.5 kw Servo will be ok to get the mill to its limit of stiffness.

I have mine with 1:1.68 for higher spindle speed, buts still ok to tap M16x1.5 with 800rpm in tool steel.

Uwe

[RJS100]

Thanks Uwe. I tend to run my machine easy. Now I just have to locate the right pulleys. The spindle diameter is 28mm and the servo is 22mm. I may have to bore out some stock pulleys.

Thanks again for all your insights... Really helpful!

[RJS100]

Quick electrical questions regarding the schematic:

1. I have never used an solid state relay before. Does this look workable:



2. I never ordered an EMI filter for a servo: Do I need one for L1 and L2 (each leg of the 220 volt circuit) Is this ok:



3. On the analog signal leaving the Acorn board, there is a snubber & resistor noted as "Snubber 2x 0,1µF + 10ohm". Not sure what the 2x means. Is this ok:

https://www.ebay.com/itm/165328404530?h ... R6ao2aOWYw

4. The schematic shows a normally closed reset switch for the servo driver. Is this simply used to cut all power to the servo. Is there any other time it is used?

Thanks as always... Richard