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Messages - macchi

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General Mach Discussion / Re: Gaining .0001 steps
« on: May 24, 2013, 08:48:03 PM »
Not a dumb question and to be honest I'm not 100% sure either.  I *think* all I've done is change the cutoff of the low pass filter; so some extra noise might make it to the microcontroller, but that should only result in skipped steps, nothing more.  Not an expert by any means though!

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General Mach Discussion / Re: Gaining .0001 steps
« on: May 24, 2013, 12:48:25 PM »
Woops, here is the image with the new resistors.

Freddy

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General Mach Discussion / Re: Gaining .0001 steps
« on: May 24, 2013, 12:41:51 PM »
Now, regarding the missed steps, Lewis to be honest I don't know if my system started to lose them right after a Mach software update.  I did go from  "Mach3_Sherline_V2.04" to R3.043.066 long before I noticed the problem, but I've used my mill rarely these past few months and I don't recall any recent intense direction reversal operations like peck drilling that would have made the problem evident.  In my troubleshooting I did try to revert to the older software and this did not resolve the issue.

I've attached some more scope screenshots that show what may be causing the problem in my system.  "DirectionalSignal" shows the direction signal coming from the parallel port in green and the direction signal at the input to the microcontroller in the Sherline control box in yellow.  The scope is capturing the change in the direction signal from high to low as Mach is trying to reverse the motor direction.  You can see how the input signal to the Sherline microcontroller rolls off by about 40 usec compared to the raw output from the computer.  Since the next motor pulse occurs about 40usec after the direction change (not shown) I'm guessing that the rolloff in the direction signal confuses the Sherline microcontroller into pulsing the motor in the pre-change direction.

I reduced the rolloff by decreasing the resistor value in the RC filter that separates the Sherline microcontroller input from the raw signal from the parallel port (from 1000 Ohm to 100 Ohm) and the improved signal can be seen in the "DirectionalSignalSharp" image.  Again the raw parallel port signal is green and the one at the Sherline microcontroller pin is in yellow.  A picture of my lousy resistor soldering job is also attached. The rolloff at the input to the Sherline microcontroller is gone and the system now seems to be working without losing steps.  The milling machine is up to ~2000 and counting rapid direction reversals without any step loss.

One last consideration if you are using the Sherline controller box, the power coming out of the box does seem to decrease with time.  For instance the hold torque on my Z channel has dropped off quite a bit so I am now using the A channel to run my Z on the mill.  From past experience replacing the SLA7044M chip solves this problem.  These chips get pretty hot and I'm wondering if there isn't enough cooling going on in the box....

Hope this helps!!

Freddy

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General Mach Discussion / Re: Gaining .0001 steps
« on: May 24, 2013, 12:02:16 PM »
Hi guys!

First off, Brett I have attached scope screenshots turning the 1/2 Sherline mode on and off.  Direction signal is green and pulse signal is yellow.  It appears to me that there is no difference in the direction signal and that the pulse signal is widened to ~40usec in Sherline mode whereas it is however wide you set it in the motor tuning window in the non Sherline mode (in this case 10usec set by me).  Note also that my scope doesn't pick up the narrow non-Sherline pulses at the 5ms timebase resolution, but they are obviously there.

Freddy

5
General Mach Discussion / Re: Gaining .0001 steps
« on: May 23, 2013, 12:48:18 PM »
Hi guys,

Just joined the forums after finding this thread, after several years of good operation the exact same problem as described by Lewis has popped up with my Sherline mill and lathe, both setup using the Sherline box.  All attempts at changing Mach software settings were fruitless, so I got out the oscilloscope and starting probing around.  The Mach output signals from the parallel port seems good, with ~40usec separation between the direction and step pulses and nice sharp transitions, but the direction signal at the microcontroller pin inside the Sherline box gets smoothed out on the downward edge only, making it likely that the step pulse immediately after this change in direction is counted for the opposing direction.  The net result is that one direction change is OK but the reverse direction change misses a step.  Accounting for this step error in how the Gcode is written does fix the problem, but of course the coordinates shown in Mach3 no longer represent reality.
I have two of the Sherline boxes and will probe all x-y-z-a channels to see if this problem occurs on all of them.  In the meantime, is it possible in Mach3 to adjust the separation time between a change in direction pulse and the next step pulse?  Otherwise I need to try to sharpen up the direction pulse in hardware somehow.

Really appreciate this thread and everyone's contribution to it!

Freddy

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