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Author Topic: lack of power when using invertor ?  (Read 5301 times)

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Re: lack of power when using invertor ?
« Reply #10 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.   

Offline mc

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Re: lack of power when using invertor ?
« Reply #11 on: January 18, 2015, 06:29:12 AM »
Geh, most CNC lathes are a fixed belt drive from motor to spinlde.

What we really need to achieve first before worrying about what mode the VFD is running, is to figure out why the commanded speed doesn't match the actual speed. For this we need to know how the VFD is being controlled by Mach, and if there is any pulley ratio between the motor and spindle.

Without those details, we could spend lots of time speculating about possible checks/settings and still be totally wrong, so until Fred provides more details, there's not much point discussing things.
Re: lack of power when using invertor ?
« Reply #12 on: January 18, 2015, 10:52:14 AM »


Hi Guys--

Not to be too critical- and sincerely appreciative of all the comments and suggestions
 but we are getting away from the subject

my original question revolved around :-

>>"It seems to me that the new motor does not have the power that the original
>>motor had. Perhaps it is just my imagination but for example turning 50mm dia
>>delrin rod at 1500rpm i can only comfortably take a 0.5mm cut depth  at a feedrate of
>>0.35 per rev .
>>Does this sound about right  ??
>>when I used the machine with the 750 watt motor i seldom used more than
>>900 rpm because the gearbox was to noisy. but still at 900 rpm i could take a
>>reasonable cut "


Perhaps there is someone out there who can comment from experience on another
machine whether this is indeed a realistic expectation ?
think of the trees-- use both sides of the computer paper
Re: lack of power when using invertor ?
« Reply #13 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. 



 
« Last Edit: January 18, 2015, 03:03:30 PM by geh7552 »

Offline mc

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Re: lack of power when using invertor ?
« Reply #14 on: January 18, 2015, 04:08:23 PM »
Geh, I know Fred mentioned gearbox, but it needs clarified.

As per this post
Quote
I think i found something

I obtained a rev counter and when the spindle is turning at 1200 rpm
the motor is only turning at 500 rpm.
 
If I crank up the speed using S1600 i get a message "set to max - to fast for the pulley?? ( or something similar)
Is there somewhere to tell it what the pulley ratio should be.
regards  
While i search the forum for pulley ratio

The spindle isn't turning at 1500rpm, it's turning a lot slower.
Which is why I'm asking how the VFD is controlled from Mach, and what ratio is involved.

As per Fred's question about cutting power, having just ran the figures through HSM Adviser, those figures suggest a cutting torque of 2.7Nm or 0.15kW at 1500rpm, so there is obviously something wrong, but we need information about the machine to find out why.
Re: lack of power when using invertor ?
« Reply #15 on: January 19, 2015, 05:11:30 AM »
Thank you MC--  You have confirmed what i suspected and thatn is that there is something wrong
What is this "HSM adviser" you talked about??

regards

fred
think of the trees-- use both sides of the computer paper

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Re: lack of power when using invertor ?
« Reply #16 on: January 19, 2015, 05:43:20 AM »
http://hsmadvisor.com/
I paid for a license a couple years ago when it was on offer, and it comes in very useful for getting pretty reliable numbers for new materials/cutters.

FSWizard is a free online version - http://zero-divide.net/?page=fswizard
I paid for HSMAdvisor as it means I can have it in the workshop without relying on a interent connection.
Re: lack of power when using invertor ?
« Reply #17 on: January 19, 2015, 01:07:03 PM »
Fred, what was the speed of the original motor.
Re: lack of power when using invertor ?
« Reply #18 on: January 20, 2015, 01:16:52 AM »
I will look tonight - I think it was 1200 because I kept the same pulleys on the motor. and on the
gearbox. If it was not 1200 then I will post the size when I know what it is

regards
think of the trees-- use both sides of the computer paper