Spindle Motor on PM-30MV Integration into Acorn

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Accu-Slice
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Spindle Motor on PM-30MV Integration into Acorn

Post by Accu-Slice »

I recently converted my PM-30MV mill to CNC. However, the spindle motor in not integrated into the Acorn software. It appears that there are three possible ways to integrate the spindle motor into the Acorn software.

1. Rewiring the PM spindle motor module as Franko did in a video series several years ago
2. Replacing the spindle motor with a VFD motor
3. Replacing the motor with a Servo motor

What would be the best way to integrate the spindle motor to take full advantage of the Acorn software? What are the perceived advantages or disadvantages of any of these methods.

Also it does appear that integrating a rotary encoder requires some custom assemblies. Is this commercially available.

Thank in advance for your input on these issues.
suntravel
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by suntravel »

Option 3 is best IMHO, did this shortly with a similar mill.

https://centroidcncforum.com/viewtopic.php?f=60&t=6572

I milled all the mounting parts myself, should be no problem for you since you already have a CNC mill.

Regards

Uwe
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by tblough »

If you don't need spindle orient, then option 2 is the best as that is what Acorn (and all of Centroid's) controls were designed for.
Cheers,

Tom
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suntravel
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by suntravel »

tblough wrote: Mon Jan 24, 2022 9:22 am If you don't need spindle orient, then option 2 is the best as that is what Acorn (and all of Centroid's) controls were designed for.
Do you think it makes a difference for Acorn if it controls a VFD or a Servo drive in speed mode with 0-10V ?

Regards

Uwe
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by firebrick43 »

suntravel wrote: Mon Jan 24, 2022 9:50 am
tblough wrote: Mon Jan 24, 2022 9:22 am If you don't need spindle orient, then option 2 is the best as that is what Acorn (and all of Centroid's) controls were designed for.
Do you think it makes a difference for Acorn if it controls a VFD or a Servo drive in speed mode with 0-10V ?

Regards

Uwe
In cost it does.
suntravel
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by suntravel »

In performance and weight also...

Uwe
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by firebrick43 »

suntravel wrote: Mon Jan 24, 2022 10:34 am In performance and weight also...

Uwe
In performance not so much unless you wish to do ridgid tapping or orient. Even 1000:1 vfd rated motors have a hard time down at 1 hertz or so. If your thread milling with a single point, or have a floating tap holder, then a servo has no advantage. There is no more power in a KW of a servo motor than in a KW of and induction motor. And induction motors are full torque at zero rpm.

Weight might be a consideration. But typically, in machine tools of this size and speed they need more mass, not less. counterbalances deal with the forces on the ball screw. More mass dampens vibration. In a mold making machine cutting cutting speeds (not rapids) with very small cutters at 500 inches a min or more, weight of the spindle motor becomes more of an issue. I highly doubt most using an acorn are dealing with such fast acceleration/deaccel of the axis.
suntravel
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by suntravel »

I switched from VFD to Servo, even at the same rpm the milled surface is cleaner with the servo.

Since the TO asked for an encoder, he will do rigid tapping maybe.

If you consider for a PM30 mill a VFD and have to by floating tap holders and build counterweights, a servo could have less costs over all.

Syncron Servo could have more torque at low rpm than a asyncron VFD drive as far as I know.

Uwe
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by firebrick43 »

After looking at your build, I have no doubt in the least bit that your cuts are smoother when you replaced your old motor.

I have seen the same results in hanging a high quality motor/pulleys/good belts on a lot of machines. Its the balance, bearing quality, shaft runout, pulley concentricity and belt quality/design that makes the difference, not the motor design per say. There are many high quality surface grinders that run the spindle with induction 3 phase motors and give a flawless finish. A wobble in the pulley or a delaminating belt will show up in the surface finish without a doubt.

You can ridged tap with a vfd and encoder, at least with normal size taps. Little bitty ones are likely to break as the when it come to a stop/start that first few micro sec is not as controlled as a servo. I can hang a quality baldor or leeson motor and vfd for at least 1/2 the cost of a servo if new and less than a 1/4 by buying a nice used motor on ebay and rolling a new set of skf or nsk bearings into it. 3 phase motor in like new condition are dirt cheap here in the states.

You would want a counter weight anyways, it saves the z axis. And floating tap holder are not that expensive. Or you could just thread mill.

1.5 kw is 1.5 kw. 2 hp is 2 hp. Hp= (speed x torque)/5252
If you double speed, you halve toque and vice versa. There is no free lunch.

The design of the motor (how many poles mainly) and size of the winding is the main determination of torque.

A 4 pole motor will have twice the torque at 1800 rpms that the same hp two pole motor has at 3600 rpms. An 8 pole motor will have twice the torque of a 4 pole motor at 900 rpms. And nearly all AC motors now are 3 phase motors.
suntravel
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Re: Spindle Motor on PM-30MV Integration into Acorn

Post by suntravel »

Well costs in germany are different, but I compared new stuff.

2 pole 1.5kw 210€ Delta EL VFD 250€ SK30 Tapping holder 175€ collet 17€ each

1.5kw JMC Servo with driver 559€

2 pole 1.5kw torque @2880 rpm 5 Nm 80% at 300 rpm
Servo 1.5kw torque 0-3000 rpm 5.73 Nm up to 14.33 Nm for short time

Noise is better with servo also because they dont need a fan for cooling.

Rigid tapping or forming M3 / 2000rpm works with 0.2s deceleration time, never broke a tool

For constant speed like a surface grinder there is no benefit for a servo IMHO

All our 80 CNC machines in my day job have servos for the spindle also.

Uwe
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