Messages

621

General Mach Discussion / Help Please with PWM Spindle Motor Speed

« on: November 16, 2014, 07:05:27 PM »

Ok, here are a couple of ideas.  First, let's assume that the controller wants to receive a PWM signal at its input at a frequency between 1 and 10 kHz, which is what the spec says.  If this is correct then the controller just uses that to switch the supply to the motor on and off with the varying mark/space ratio that Mach puts out, which should vary the motor speed in the expected way.  You have set the PWM base frequency to 2500 Hz which is in the range suggested.  Unfortunately the way that Mach works is that the mark/space ratio is derived from the kernel speed.  Supposing that the kernel speed is set to 25 kHz which is suggested in the manual, there are only 10 discrete pulse lengths of a  2.5 kHz signal that Mach can generate.  You would not therefore expect to see a very smoothly varying speed.  One way to check this would be to set the PWM base frequency to something very low, like say 2 Hz.  If the controller works in the way we are assuming, you will find that the motor runs very unevenly, as it will be starting and stopping twice a second.  IF the controller works in this way then it isn't really compatible with Mach.

So could I suggest that you try this test and report what you find.  Depending, we can think again about what to do.


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622

General Mach Discussion / Help Please with PWM Spindle Motor Speed

« on: November 16, 2014, 07:23:09 AM »

I suspect you may have a couple of basic problems.  First it is likely that the PWM speeds controller you have need a voltage between, probably, 0 and 10 v to set motor speed.  However to confirm this you need to provide more than a photo, we need to have its specification or a link to one.

Second, you don't say how your PC is connected to the controller.  Assuming you have a breakout board, the PWM output from this is just a train of 5 volt (usually) pulses of varying mark/space ratio, which needs converting to the control voltage.  Again, we need to know details of the BoB to confirm this.  Unless it does the conversion internally you would need something between it and the controller to do it, it's only a simple circuit and several have been published.

Third, the PWM base frequency you have set is far too high by a factor of 100.  Something like 25 to 50 Hz is better to get smoother control.

Once you have this working the pulley ratio is irrelevant as your spindle doesn't have pulleys.

Please give us more information, on the breakout board type and controller type!


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623

General Mach Discussion / Setup advice needed for Newbie

« on: November 08, 2014, 05:38:10 PM »

Roger, I never thought of that, what a good idea!  Thanks.


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624

General Mach Discussion / Setup advice needed for Newbie

« on: November 07, 2014, 02:46:58 PM »

And yes, z is negative towards the headstock, x is nominally zero when the tool is on the spindle axis and increases positive as the tool moves towards you.


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625

General Mach Discussion / Setup advice needed for Newbie

« on: November 07, 2014, 02:43:36 PM »

Normally you set the tool lh edge on the face of the work and zero the z dro.  Set the tool on the periphery of the work and set the x dro to the diameter of the work (assuming you are working in diameter mode).  This also assumes that the end of the work is faced off and the work is cylindrical and coaxial with the spindle.  Unless you have ballscrews on your lathe don't try backlash compensation, in my experience it doesn't work for the levels of backlash you get on normal lathe feed screws, and anyway with a lathe you tend always to be cutting in the same direction.

And yes, z is negative towards the headstock, x is nominally zero when the tool is on the spindle axis and increases positive as the tool moves towards you.


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626

General Mach Discussion / Internal Error B109-13: Cannot decompress setup program

« on: November 05, 2014, 03:57:32 PM »

As well as Hood's point, you might want to download the latest Mach 3 image from the website.


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627

General Mach Discussion / 2.5 vs 3 axis whats the difference

« on: November 05, 2014, 03:55:03 PM »

I think the point he's making is that if you clamp something to the table and move the table in only xyz, you can't undercut the shape, which is kind of obvious really.  Clearly you could use a ball nose cutter and make a shape which is everywhere convex or concave wrt to x and y, but it couldn't be concave wrt to z if you see what I mean.  You could imagine a tool which is a bit like a tee slot cutter, but even them there would be limitations on undercut.  On the other hand if you could rotate the work around the x and y axes then undercut is obviously possible.


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628

General Mach Discussion / wrong axis movements

« on: November 05, 2014, 03:46:44 PM »

And your leadscrew pitch is?


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629

General Mach Discussion / Re: Closed loop system, encoder connected to mach3

« on: October 26, 2014, 03:13:07 PM »

So, when you energise a stepper system from cold, is it instantly in the correct phase to move properly?
I need to read up on steppers

No!  That's why if you close down Mach and "save fixture", and try to start again from cold, the stepper may move a little when re-energised and be in a slightly different plave from where they were when closed down.  When I turn the drivers off or on there is a thump from the drives as they move slightly to align with wherever the drive phases are.

But yes, it can now move properly from wherever it now is but that wasn't quite where you left it. 

630

General Mach Discussion / Re: Joy Stick

« on: October 26, 2014, 03:06:36 PM »

...and it's an Xbox 360 controller...