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I purchased:MD001 8 years ago and now just getting to work on it. I retired and moved to Texas. Built my new shop and finally finished it. I needed to build my cnc router so I could machine my parts. I’m really excited to get started on this project. Thanks for your feedback

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I’m going to cut dovetails off so I can put linear bearing on to replace dove tails. I bought linear bearing on eBay and I think I can use my cnc router to cut dovetails off. I’m going to try 4 flute carbide end mill at 3000rpm and 17im .0625 depth of cut. I’ve never cut cast iron on my router but that looks like the only option at this time.

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Fired up router full expecting to break my bit but cut both table and column with same bit. Took little over 6 hrs for table and 4 hrs for column.

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Finished cutting now I need to mount linear rails. Ordered bolts and waiting for them to get here.

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I

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I originally purchased DMM servo’s for this build but digging through my servo pile I think I’m going to use these instead. I have not looked into wiring for encoders to drives I have but I’ll need to research wiring I also originally purchased a Chinese BT30 ATC spindle when I started this project.

[joeavaerage]

Hi,
how many cars do you have on each rail? The picture shows just one. Two cars per rail is the norm and very much more stable.

Craig

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The cars are 6.875” long. When I originally purchase these on eBay I was going to put 2 per side till I got them and saw how big they were.

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I was going to make my ATC air cylinder but digging thru my junk cylinders a found 5 Fabco-Air cylinders. This one has 1" stroke, but I think it is pull not push. If anyone has information about this cylinder, please let me know. Thanks

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My spindle servo is rated at 10.5 Nm and 3000 rpm’s. If I drive it 1:2 to get 6000 rpm’s will that kill my torque. I would like to not have to manually change gear ratios if I can get away with it.

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Took Fabco stacked cylinder apart and it was pulling cylinder. I wanted to rebuild it anyway. If you flip everything over, you can reverse force direction. Fabco-Air Inc. has drawings and chart for power. This is a 3" piston that has little over 2,000 lbs. force at 100 psi. with 1" stroke. I like the fact that you don't have to run air lines to each individual cylinder. From what I see I think that's going to work.

[joeavaerage]

Hi,
is the spindle a repurposed AC servo or is it a genuine spindle motor?

My Delta servos are rated to 3000rpm but have a maximum of 5000rpm. They generate rated torque at rated speed, but at higher speeds the torque linearly diminishes as the speed increases.
The is a common property of AC servos and is called 'Field Weakening'.

You may have noticed that AC motors intended for spindle service are actually very much like AC servos, they have an encoder and a matching drive. They will often have a rated speed of 2000rpm and a rated torque
of 20Nm........but they can still run at 8000rpm??? How is this possible? It is due to field weakening.

An AC servo is an example of a Field Oriented Controlled motor. It has an encoder to accurately monitor the angular position of the rotor. The three phase currents that are supplied to the motor are precisely calculated
to produce a combined magnetic field at 90 degrees to the rotor, thereby getting the maximum torque for the least current. A few microseconds later and the rotor has turned a little, the applied currents are recalculated
so that they remain 90 degrees to the rotor. Very clever, and describes why servos have such good torque production for their size.

One property of a motor is called the 'Back EMF Constant'. As the motor spins it generates a back voltage. So at a given or max speed, the back EMF is nearly equal to the applied voltage and therefore the motor can
go no faster. The strength of the magnetic field of the rotor is very significant in determining what the back EMF is and therefore determines the max speed.

One of the things that you can do with Field oriented control is to provide the three phase currents such that there is a component of the net magnetic field that is 90 degrees to the rotor and produces torque,
but also supply some current that opposes the magnetic field of the rotor. This has the effect of reducing the magnetism of the rotor (field weakening) and thereby reduces the Back EMF and allows the motor to go faster
for a given input voltage. Very clever....but its not a free lunch, the torque output is reduced.

Lets say our spindle motor from above has 20Nm torque at 2000rpm. At 8000 rpm the torque is 20 x (2000/8000) = 5Nm This is how a spindle motor can produce really high torques at slow speeds, it is when all said
and done a low speed high torque motor, but because of the wrinkle called field weakening can still spin really fast as well. The best of both worlds. Servos use the same principle but usually less dramatically.

Craig

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This is the servo I'm planning on using. I hope this helps.
Greg

[joeavaerage]

Hi,
without knowing what servo drive you have I would guess it to be similar to my Delta servos, ie rated to 3000rpm but have a modest overspeed region using
field weakening. It might be possible to push that servo to 4000rpm, 4500rpm, or maybe even 5000rpm.

Craig

[joeavaerage]

Hi,
even if you do use field weakening to extend the speed envelope of a motor you still suffer exactly the same torque reduction as you would with a gearbox or belt increase.

Lets say a servo has 10.5Nm at 3000rpm. Assuming you can use field weakening then at 6000rpm you'd have 10.5 x ( 3000/6000)=5.25Nm.

If you used a gearbox (with no losses) then 1:2 speed increase will result in a 2:1 torque reduction ie 5.25Nm.

The only advantage of field weakening is that it avoids for the need of a gearbox, the losses associated with the gearbox and the drag of having to changes gears all the time.

Craig

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This is the drive I'm going to use.
Thanks Greg

[joeavaerage]

Hi,
you need to get the set-up and tuning software for this drive.

On page 79 of the manual it shows the dialogue to set the motor, including the max rpm. Note also that you can nominate a specific matching servo from a database and the database will populate the motor parameters.
I have an Allen Bradley servo that does the same thing. The only problem is that if the max speed is set by the database you cannot arbitrarily set it higher. With my Allen Bradley servo for instance that
means that I cannot run it faster than rated speed because the software does not allow it. Maybe Kollmorgen have done it differently. It would be nice to extend the speed range of that servo, but it is possible that
the software and/or drive do not permit field weakening. Get the software and try it out.

Craig

[grg_p]

Thanks for the advice, Craig. After looking at options going with single drive 1:2 belt is going to cut my torque in half all the time vs twin drive belt which will only cut my torque when in high spindle speed. The field option is intriguing but looking thru manual I don't think that is an option. It looks like the drive needs a large resistor to handle excess voltage generated. I don't know how much I will need to use high speed spindle settings. So just using 3,000 rpm might be the option. My router goes to 22,000 so I can possibly use it if need be. I've cut stainless and metal on it. But if I do a twin belt, I'm leaning toward air shifting 2 speeds, so I don't have to adjust belts. I find if you have to spend time setting up machines you tend to find a way around it. Thanks again for clearing that up Craig you have excellent knowledge of subject.

[joeavaerage]

Hi,

It looks like the drive needs a large resistor to handle excess voltage generated.

The braking resistor has absolutely nothing to do with it.

Craig

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Field Weakening
Overview
As motor velocity increases so does the induced back EMF voltage. If large enough, this induced back EMF voltage can limit the inverter's ability to produce current. When this happens, it can be observed that the current feedback cannot follow the current command, and velocity cannot go above a certain limit (called base speed). This base speed depends on the motor parameters as well as the available dc bus voltage.

To go above the base speed, the field weakening loop is activated using the AXIS#.MOTOR?.FIELDWEAKENING keyword. Once activated, the field weakening control loop monitors the magnitude of the motor-voltage vector. If this magnitude gets close to the available bus voltage, it increases the d-axis current to reduce the back emf voltage of the motor and, as a result, limits the magnitude of the motor-voltage vector. Therefore, it can go above the base speed of the motor while operating at Maximum TorqueClosed per Volt (MTPV) condition.

The field weakening control loop is configurable using the following keywords:

AXIS#?.FIELDWEAKENING?.CURRFILTERBW
AXIS#.FIELDWEAKENING.LOOPBW
AXIS#.FIELDWEAKENING.VBUSMARGIN
AXIS#?.FIELDWEAKENING?.VOLTFILTERBW
For more information on configuring the field weakening loop, see the keywords above.

Usage and Safety Considerations
Kollmorgen recommends that the field weakening control loop is used in velocity or position modes but not in the torqueClosed mode.

The field weakening algorithm works with the foldback algorithm to ensure the magnitude of the current vector applied to the motor is always within the safe limits for both motor and the drive. For more information on foldback algorithm see Foldback.

The applied q-axis and d-axis currents are also limited by:

AXIS#.MOTOR.IPEAK
AXIS#.MOTOR.IDMAX
AXIS#.IPEAK
AXIS#.IL.LIMITP
AXIS#.IL.LIMITN
Set AXIS#.MOTOR.IDMAX appropriately to prevent demagnetization of the permanent magnets inside the motor when operating in the field weakening mode.

The field weakening algorithm can support both surface permanent magnet and interior permanent magnet motors:

AXIS#.MOTOR.TYPE = 0 or 6


When operating in the field weakening mode, the drive is artificially lowering the induced back emf voltage of the motor by applying whatever d-axis current that is necessary. If a fault happens while operating above base speed and the power stage disables, the d-axis current-flow stops and a back emf voltage that is higher than the bus voltage is created.

To ensure operational safety of the drive in such condition, the velocity fault threshold AXIS#.VL.VFTHRESH is always limited by the over-voltage fault-threshold of the drive. AXIS#.VL.VFTHRESH is also limited by AXIS#.MOTOR.VMAX , which is the maximum mechanical velocity limit for the motor, as well as AXIS#.VL.THRESH, which is the user-defined velocity threshold.

Exercise care when using field weakening because the induced back emf voltage of the motor is no longer limited by the available bus voltage of the drive.