Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[Jon Elson]

On 02/02/2017 10:06 AM, James Reed wrote:
> The spindle brake is usually something that holds the spindle after stopping. 
>  I believe my Bridgeport has a ratchet which engages a gear.  Obviously, I 
> don't want to try to use that to bring the spindle to a stop.
>
>
All of the Bridgeports I've worked on had a band brake that 
gripped the driven pulley of the belt drive, and could be 
engaged safely from full speed.

Jon

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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[Jon Elson]

On 02/02/2017 09:42 AM, dragon wrote:
> Ed Fanta does rigid tapping on his CHNC. I don't believe that he has a
> breaking resistor on the VFD even. IIRC I watched the output of the
> SPINx1 and it just goes from a + voltage to a - voltage and does not
> "stop" he does have a fairly high line count BEI(?) encoder on the spindle.
>
>
Many VFDs have internal braking resistors.  The braking 
resistor is NOT specifically limited to stopping the motor.
It is used any time the bus voltage rises, as it certainly 
will when reversing the motor.  The resistor absorbs the 
energy removed while the motor is being slowed.  The braking 
resistor works great on my Bridgeport mill when doing rigid 
tapping.  Doing it on a lathe with a big chuck would make it 
even more important.  If the bus voltage rises too high 
without a braking resistor, the drive will get an 
over-voltage fault and go to coast mode, which will not be 
good for your tap or workpiece.  I used a vitreous enamel 
power resistor for the braking resistor on the Bridgeport, 
and two of them on my Sheldon (manual) lathe.  The braking 
resistors made specifically for VFDs are really expensive, 
must have something to do with safety certification or 
something.  I've heard of people using stove heating 
elements.  In fact, Haas machine tools have such an element 
in the cabinet!

Jon

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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[Ed]

On 02/02/2017 09:42 AM, dragon wrote:
> Ed Fanta does rigid tapping on his CHNC. I don't believe that he has a
> breaking resistor on the VFD even. IIRC I watched the output of the
> SPINx1 and it just goes from a + voltage to a - voltage and does not
> "stop" he does have a fairly high line count BEI(?) encoder on the spindle.
>
> It works very well for him and he taps at surprisingly high spindle speeds!
>
No braking resistor and it still stops in 1/2 revolution at 200 RPM, 600 
RPM it stops in 2 revs, above that it is slower to stop. It has mounted 
a 6" power chuck to add to the spindle mass. With a 16C collet it stops 
much faster. It is running a Toshiba VFD rated at 7 1/2 HP.

Ed.


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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[Gene Heskett]

On Thursday 02 February 2017 10:29:11 Jim Craig wrote:

> On 2/2/2017 9:13 AM, John Thornton wrote:
> > I also have an Automation Direct GS2 on my BP knee mill and rigid
> > tap with it (need the braking resistor).
> >
> > JT
>
> John,
>
> That is an interesting point. I am getting ready to add gear tooth
> sensors on the bull gear so I can rigid tap. I don't have a braking
> resistor on my drive. Currently the mechanical spindle brake engages
> when the spindle stops via a pneumatic cylinder. To be honest I am not
> sure if it would engage during a spindle reversal as I don't do that
> currently. It probably would not. Does the rigid tapping cycle stop
> the spindle or does it do a reversal without stopping? M3 M5 M4 M5 or
> M3 M4 M5?

There is no stop between m3 and m4, so I have had to cobble up some hal 
stuff to ease the violence of the reversal that Jon's PWMservo driver 
can do.  Other wise it breaks drive parts on TLM. I also slow that on 
the G0704 in order that Z can keep up with it. I've about 1/2 second of 
delays there. Experimentally, the reversal this "fake" vfd can do can be 
unbrutalized, but it takes a minimum HZ setting lower than would be safe 
for the motor over an extended time period to make it really smooth. The 
problem is the stopping DC braking is either not effective, or damed 
brutal from 300 motor shaft revs.

> I figured that the drag from tapping would stop the spindle pretty
> quickly without the resistor. I would like to hear more about your
> experience with this situation.

VFD's are 4 quadrant controls Jim, as is Jon's pwm-servo amp. They have 
as much power slowing the motor as they do speeding it up, until the 
rotating field is too slow in the vfd case, 10 hz perhaps, then they can 
put some dc thru the coils to finish the stop.  Its a  balanceing act to 
get that right. The vfd can handle that, but with the servo amp, I don't 
allow the reverse to go on thru to the controller until the encoder says 
its been stopped for a couple milliseconds. I may do a similar thing on 
this Sheldon, but I suspect the vfd can handle that good enough.

> Thanks,
>
> Jim
>
>
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Cheers, Gene Heskett
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-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[James Reed]

The spindle brake is usually something that holds the spindle after stopping.  
I believe my Bridgeport has a ratchet which engages a gear.  Obviously, I don't 
want to try to use that to bring the spindle to a stop.

The reason you need a braking resistor is to dissipate the back emf from the 
motor after a rapid decel.  If you don't perform too rapid of a decel, then the 
braking resistor is not required.  I would imagine, from all I have seen, that 
rigid taping would usually require a braking resistor, even if the decel was 
caused by drag on the spindle.  I typically pick a VFD one size larger than 
what is required to help mitigate the need for a braking resistor.  If the load 
is high inertia, or a heavy load, I will go 2 steps up in size and then still 
use the braking resistor.



From: Jim Craig <jimcraig5...@windstream.net>
Sent: Thursday, February 2, 2017 3:29 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] VFD recommendations - braking resistor vs mechanical 
brake.

On 2/2/2017 9:13 AM, John Thornton wrote:
> I also have an Automation Direct GS2 on my BP knee mill and rigid tap
> with it (need the braking resistor).
>
> JT
John,

That is an interesting point. I am getting ready to add gear tooth
sensors on the bull gear so I can rigid tap. I don't have a braking
resistor on my drive. Currently the mechanical spindle brake engages
when the spindle stops via a pneumatic cylinder. To be honest I am not
sure if it would engage during a spindle reversal as I don't do that
currently. It probably would not. Does the rigid tapping cycle stop the
spindle or does it do a reversal without stopping? M3 M5 M4 M5 or M3 M4 M5?

I figured that the drag from tapping would stop the spindle pretty
quickly without the resistor. I would like to hear more about your
experience with this situation.

Thanks,

Jim


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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[dragon]

Ed Fanta does rigid tapping on his CHNC. I don't believe that he has a
breaking resistor on the VFD even. IIRC I watched the output of the
SPINx1 and it just goes from a + voltage to a - voltage and does not
"stop" he does have a fairly high line count BEI(?) encoder on the spindle.

It works very well for him and he taps at surprisingly high spindle speeds!

On 02/02/2017 09:29 AM, Jim Craig wrote:
> On 2/2/2017 9:13 AM, John Thornton wrote:
>> I also have an Automation Direct GS2 on my BP knee mill and rigid tap
>> with it (need the braking resistor).
>>
>> JT
> John,
> 
> That is an interesting point. I am getting ready to add gear tooth 
> sensors on the bull gear so I can rigid tap. I don't have a braking 
> resistor on my drive. Currently the mechanical spindle brake engages 
> when the spindle stops via a pneumatic cylinder. To be honest I am not 
> sure if it would engage during a spindle reversal as I don't do that 
> currently. It probably would not. Does the rigid tapping cycle stop the 
> spindle or does it do a reversal without stopping? M3 M5 M4 M5 or M3 M4 M5?
> 
> I figured that the drag from tapping would stop the spindle pretty 
> quickly without the resistor. I would like to hear more about your 
> experience with this situation.
> 
> Thanks,
> 
> Jim
> 
> 
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Re: [Emc-users] VFD recommendations - braking resistor vs mechanical brake.

[Jim Craig]

On 2/2/2017 9:13 AM, John Thornton wrote:
> I also have an Automation Direct GS2 on my BP knee mill and rigid tap
> with it (need the braking resistor).
>
> JT
John,

That is an interesting point. I am getting ready to add gear tooth 
sensors on the bull gear so I can rigid tap. I don't have a braking 
resistor on my drive. Currently the mechanical spindle brake engages 
when the spindle stops via a pneumatic cylinder. To be honest I am not 
sure if it would engage during a spindle reversal as I don't do that 
currently. It probably would not. Does the rigid tapping cycle stop the 
spindle or does it do a reversal without stopping? M3 M5 M4 M5 or M3 M4 M5?

I figured that the drag from tapping would stop the spindle pretty 
quickly without the resistor. I would like to hear more about your 
experience with this situation.

Thanks,

Jim


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