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Messages - geh7552

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121
General Mach Discussion / Re: Z axis incorrect
« on: February 06, 2015, 07:22:13 PM »
I assume the motors are 200 steps per revolution (there are some old 180 step motors still around but it's not likely you have one) the Gecko G540 is x10 microstepping. The ball screws are 5mm pitch. So doing the math, 200 x 10 = 2000 pulses per rev, divided by 5 mm = 400 steps per unit.  Go into Mach 3 motor tuning and enter 400 in the steps per unit for each axis (X,Y,Z). This will equal 400 steps to travel 1mm.

This is only the calculated values and in a perfect world would be exact, but the actual distance traveled may vary slightly due to ball screw precision. Next use Mach 3 calibration function and follow the instruction on the popup window... enter a distance value and then measure the travel with a digital caliper. This will correct the steps per unit numbers.

    

122
General Mach Discussion / Re: Z axis incorrect
« on: February 06, 2015, 10:47:21 AM »
Check to make sure steps/unit is correct in motor tuning.

123
General Mach Discussion / Re: Vibration At Low Speed! Help please!
« on: February 06, 2015, 10:44:41 AM »
No video... blank screen.

124
General Mach Discussion / Re: Driver gone crazy
« on: February 03, 2015, 11:37:34 AM »
Electronic devices don't last forever... if you traced it to one bad driver then it probably needs to be replaced.

125
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 18, 2015, 02:59:44 PM »
MC, Fred stated his lathe has a gearbox. Agreed there are allot of unknowns with this problem due to lack of information. Fred seems like a nice guy BUT doesn't have the technical abilities to understand what he's trying to accomplish. He's missing the entire cause of the problem and focusing on why he can't take the same depth of cut and expects someone on the forum to give a "magic" answer.

First, a noisy gearbox is a sign of mechanical problems that should be addressed first. The 750W, 220V, (no given rpm), single phase motor, when geared down to 900 rpms (chuck speed?) had enough torque to make a heavy cut. Changed to a 1.1kw, 1400 rpm, 3 phase motor and VFD and can't get enough torque at 1500 rpm chuck speed to take the same cut. It's very simple... the torque ratio and rpm between the new motor and chuck is backward. 



 

126
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 17, 2015, 10:59:24 PM »
I'm not sure why Fred is using a VFD on a lathe in the first place??  Lathes have a wide range of gear combinations to get the desired chuck speed.   

127
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 17, 2015, 02:50:14 PM »
Check the Omron drive specs and it can be setup for vector mode or V/F mode with either CT (constant torque) or VT (variable torque) setting. For lathe operation I would use CT.

Some things to consider...

Most industrial motors are TEFC (totally enclosed fan cooled) with a cooling fan attached to the shaft in the endbell. Operating a motor at slow speed can result in overheating due to lack of cooling air. I don't know what type of 1400 rpm/3 phase motor you are using but running at less that 50% speed it might require external cooling blower. It doesn't take long for a motor to overheat especially under a load.

Second issue is the motor design... Motors used with VFD's are "inverter duty rated" which means the stator and rotor winding are designed with special insulation for frequency modulation and voltage spiking that occurs. Regular motors can be used but the is more probability the winding insulation will break down and short. Putting a 3 phase line reactor (choke) on the VFD output, between the drive and motor, can help eliminate spiking.  


  

128
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 16, 2015, 08:53:20 PM »
Yes, I forget to mention 2 and 4 pole motors. A 1800 rpm motor can be over driven, however, the torque curve decays rapidly as the motor exceed it's rpm design limit. So it's there is no free lunch so to speak. The other issue - and more dangerous - is the 1800 rpm rotor is larger and heavier as compared to a 3600 rpm motor. Over speeding an 1800 rpm motor can run the risk of the rotor windings de-laminating and flying apart.

I had a customer that tried to over speed a 75hp, 1800 rpm NEMA motor on a large industrial blower system... he reconfigured the drive and max rpm limit as a cheaper way to go instead of changing a $4200 motor. He looked like a hero to his boss. Worked for a couple of days. Then on day #3, at 2900 rpm's the rotor self destructed and locked dead... the 150 pound blower fan's inertia caused the motor to rip off the base destroying the blower housing. $25,000 worth of damage... priceless!  

129
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 16, 2015, 04:03:46 PM »
Could be quite a few things causing this. Again, as in your past posting with this same drive, you are not specific about the actual problem. I assume the motor is slowing down with deeper cuts. Sounds like low motor torque.

1) The VFD could not be setup properly for the motor specs (kw, voltage rating and rpm).

2) Low cost VFD's operate in what's called V/F (volts-frequency) mode, this means the output voltage to the motor reduced  as the frequency is reduced to lower motor rpm. When this happens motor developed torque is reduced exponentially... slow down the frequency enough and the motor can stall under load. This concept is a not understood by non electrical people that don't work with VFD's, then wonder why their motor is stalling or runs like crap.

The 750W, 220V motor you had operated at line voltage (220V) and developed 100% torque. I assumed the lathe speed is changed via gears or pulleys. I would use the lowest gear ratio to keep the motor rpm's in the high end to get max torque... then use the speed control pot to "trim" the rpm's to the desired lathe chuck speed. 

Industrial VFD's such as Siemens and Toshiba have a "vector mode" of operation to eliminate the torque problems with V/F mode. But you are talking about a $1500 drive instead of a $200 drive. Cheap Chinese drives are even worse for motor torque control and are garbage.     

130
General Mach Discussion / Re: Spindle overspeed
« on: January 10, 2015, 09:57:22 AM »
Does the spindle speed go to zero with the drive still in run mode or does the drive shut off completely?

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