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Messages - DMBGO

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General Mach Discussion / OD Arc wizard
« on: October 15, 2017, 03:00:51 AM »
I am trying to use the OD Arc wizard under Mach3 turn to cut a radius on the end of a rod. Here is the scenario:
I have a piece of hex bar that I want to cut a radius on the end of. I am making a few wheel nuts.
The bar is 20.4mm across the points of the hex. I want a radius that is 3mm below the edges of the hex, and covers all of the end of the bar. I am fairly sure that I have done this type of thing successfully in the past, and I seem to have in my mind that I specified a sphere diameter that was larger than the end of the bar, then used the graphic in the wizard that shows where it will cut, to fine tune the arc until it covered the end.
I am using these parameters: Z center 0, Z start 10.2, Z end 7.2. X start 10.2 X end 0
With the sphere diameter set to 20.4mm, the wizard does what I would expect, and proposes cutting a 1/2 sphere, finishing 10.2mm down the nut.
If I put a larger sphere diameter into the wizard, the image on the screen in the preview, is nothing that I am able to understand.

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,  :)


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.

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.

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.

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.

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......


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.

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

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.

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