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Inconsistent Movement in Mach 3
« on: October 11, 2008, 06:43:31 PM »
Hello,

I'm running the trial version of Mach 3 and like the features and interface very much. Unfortunately before I purchase the full version I want to make sure that it will work in my environment and this is where the problem is, my setup is as follows:

- Home made CNC from RockCliff Machine Plans (A Type at http://www.rockcliffmachine.com/cnchome.htm).
- Driver board and stepper motors are Budget Bulldog from Stepperworld (http://www.stepperworld.com/FET3bulldog.htm).
- PC has a 2GHz Pentium family (I believe PIV) processor and is running a completely stripped down version of Windows XP (no network).

Stepper World provides a program for testing their setup called VBStepDir (http://www.stepperworld.com/XPpanel.htm). When I run this program at full tilt (motor capacity is 6ipm with my setup) it runs all three axes smoothly in both directions apparently without missing a beat. While doing this all motors sound extremely smooth and have a consistent hum to them.

When I run a few test programs through Mach3 I get a very rough sound coming from the steppers, like they are definitely skipping pulses (or so I would assume). I have noticed two very repeatable traits: First, my main test program is a simple 4"X 4" square cut out of 1/4" MDF. The three that I have cut so far have all come out about between 3.72" and 3.8" to a side. The Z axis is the worst of them all, it will actually raise the rotary tool fairly well but when lowering it sounds horrible and clearly isn't responding correctly, I will jog the the rotary tool down maybe 3" - 4" but only get 1" - 1/2". If I switch back to VBStepDir and make sure that everything seems fine it will lower and raise perfectly smoothly. The net effect of this is if I cut a program with multiple pockets the z-axis will creep upwards until it hit's it's top limit.

I have configured Mach 3 as per the attached screen shots provided with the Budget Bulldog and I have verified the feed-rate (4000 ppi on a 20tpi lead screw). I have also softened the ramp-up and ramp-down speeds and have tried cutting at 6ipm, 5ipm and 4ipm with exactly the same results. Needless to say I'm stumped.

My first attempt was with an 800 MHz Celeron processor which clearly was just not fast enough because when I was running all three axes in VBStepdir they would run smoothly until I moved the mouse at which time they would start stalling. I got another computer to make sure that this was not the problem and to my surprise the problem did not go away.

I have attached a screen shot of my Mach3 Driver Test, the one thing that I can see is that the 25KHz signal is below 24Khz, could this be causing a problem with my motors, are they per chance expecting a 25KHz signal? This is the only thing I can think of.

Any help will be greatly appreciated.

Regards,

- Birger

Offline Hood

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Re: Inconsistent Movement in Mach 3
« Reply #1 on: October 11, 2008, 06:54:02 PM »
Have you tried changing the active state for the step pins? Have you tried with a bigger pulse width, maybe 5 or 6?

Hood
Re: Inconsistent Movement in Mach 3
« Reply #2 on: October 11, 2008, 07:05:37 PM »
No Haven't tried either of those. Just to make sure, when you say active you are referring to active high vs. active low? I will try both of these suggestions and post results here.

Thanks.

- Birger

Offline Hood

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Re: Inconsistent Movement in Mach 3
« Reply #3 on: October 11, 2008, 07:09:17 PM »
Yes thats correct, some drives are picky, also the dir state as well can cause problems on some drives.
Hood
Re: Inconsistent Movement in Mach 3
« Reply #4 on: October 11, 2008, 07:35:43 PM »
Thanks Hood, That did the trick, I upped the pulse width by 5 (microseconds I believe) and it is now smooth and quiet in all directions. I have also upped the rates back to 6 ipm and it works just as well. Now to figure out the hold down and I will cut another 4X4 square to validate...
« Last Edit: October 11, 2008, 07:54:33 PM by bdelapen »

Offline Hood

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Re: Inconsistent Movement in Mach 3
« Reply #5 on: October 12, 2008, 03:50:30 AM »
:)

Hood