Messages

51

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 09:09:56 PM »

Craig, I have to finish the job at hand before starting to play. If I start enjoying the rewards of my labour prematurely, I will intermittently, in the future, say to myself, I must do such and such at some stage and never get around to it. At some time another impetus will drive me to complete the work, in maybe 5 or 6 years time.
Roger, 

Cheers
Dave

52

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 08:53:46 PM »

There are always several ways to skin a feline Roger. You are right of course, but I am using this as the impetus for something that I should have done long ago.
Cheers
Dave

53

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 08:26:50 PM »

Hijack away. Here is my goal. "https://www.youtube.com/watch?v=DajrTlI8IWA" Imust admit I have no idea how I will acheive it, but you never know.
Cheers
Dave

54

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 06:26:23 PM »

I tried gardening Roger, which is why I changed to something easy like CNC instead. Thanks Craig for your input re the encoder pulses from the servo drive, but I am now down the path of making an improved version of my old spindle based encoder, so I'll keep going....
The thread has devolved into an interesting discussion on the possibilities based on a hardware encoder  on the spindle of the lathe, and I am enjoying it immensely. I bought the servos that I am using about 6 years ago and it was seeing a you-tube video showing someone cutting a hex onto a spinning shaft with their lathe, using parametric Gcode that made me extract my digit.
Cheers
Dave

55

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 06:41:37 PM »

Thanks Craig, Rich et al. I'm going to put my old hall element back as a spindle encoder and connect it to the index input. The rest, while academically interesting, doesn't sound like it makes much difference. Thanks again. I'll let you know how it goes.
Cheers
Dave

56

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 05:14:42 PM »

Craig, you said
"The actual and programmed speed should be within a few parts per million.....you are wasting time and money if you try improve on that.
No doubt if I read the manual closely there will be an encoder output. This could be used by Mach to measure the rpm and display it if
you want to be totally anal retentive about it."

Is this a common output on servo drives? Do they have a single output that has all of the encoder pulses? Is this too fast for Mach, since we are talking about 2.5 mhz at 1000 Rpm? So many questions, so little time......

Cheers
Dave

57

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 05:04:06 PM »

With 2500 available counts per rev, 1 count does just not cut the mustard (or the thread). It needs to be fed back to the system, so that one can see (on an eye candy display) any deviations that may be occurring within an individual revolution, causing unsightly, and inconvenient deviations.

58

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 08:06:55 AM »

Thanks for your in depth replies Craig. The spindle servo that I am using atm is a GSK AC servo, and DA98B servo controller from GSK as well. I know that the loop is closed in the servo controller, but I was hoping that M3 would also take this as a given since no index pulse was configured, and consequently display the commanded speed in the "Actual RPM" DRO. I haven't tried to thread with this config, since I think it will probably fail or the pitch of the thread will be wrong. This is just supposition, mind you.
Tomorrow I will reinstate my hall effect encoder for the spindle that I built about 10 years ago, when I first converted the lathe to CNC using steppers. I am using step and direction to drive the servo btw, or as our Asian brothers across the way seem to call it pulse and sign (I like the idea of a signpost to point out directions). I do have a 0 to 10v converter from Peter H, but I am not aware of any benefit in using it.
I look forward to seeing a closed loop spindle control for the ESS Roger, thanks for mentioning this.
I can't see though any shortcut that I can take atm , it looks like I will bite the bullet, and ensure compatibility etc.
I agree with GER21 unless anyone has another idea?
Oh and I have had a M4 license for some time, but I haven't been able to bring myself to undertake the required learning curve.
Thanks again
Dave

59

General Mach Discussion / Servos progressing well, but question about index

« on: September 22, 2017, 12:35:51 AM »

As mentioned in my last post, my problem with the Z axis was resolved and things have proceeded on the stepper to servo conversion of the lathe . I now have servos working well on the Z and X axis. The Spindle servo is also working (you'll notice I didn't say "well" there). According to my laser tachometer it is spinning at whatever rpm I command, and since it is a servo, I thought that M3 would take this on trust and display the commanded speed in the "Actual RPM" DRO. As I post this I am realising that M3 probably needs some type of spindle index sensor, since it would otherwise have no way of compensating for speed fluctuations when threading etc.
No point really in proceeding with my question.
Bye

60

General Mach Discussion / Re: Unusual stepper issue on lathe

« on: September 03, 2017, 07:11:17 PM »

Many thanks for your input Craig
Many years ago, when I set the lathe up, I had problems with electrical noise. I was using a USB Smoothstepper and I think from memory (always a dangerous thing), that the option to alter the noise filtering of inputs was not in the driver at that stage. Time passed and I moved to an Ethernet Smoothstepper which had the "noise filtering of inputs" option in the driver, and in conjunction with the anti-interference measures that I had already put in place for the Usb Smoothstepper (shielded cat 5 cables for motor and VFD connections etc), the lathe worked well for years.
This was a new problem that only reared its head at the last moment when I started boring the pulleys for the servo motors.
Although I may have sounded rational in my posts, a little voice inside my head was saying " you know that it is malignancy on the part of the equipment that is causing this."