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Author Topic: Behavioural Changes in Mill  (Read 3006 times)

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Offline pgh3

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Behavioural Changes in Mill
« on: April 22, 2011, 05:09:34 AM »
The marriage between Mach3 and my small CNC mill has been blossoming nicely; my last run was a 4 hour raster cut of letters into a piece of Merbau (wood).

Now, any G01 movement in X results in excessive chatter, lots of noise, no movement or erratic; and sometimes in the wrong direction.

Unless I hold down the shift key - the direction may, or may not, be reversed, but the X motor runs nice and sweet. The other axes (Y and Z) all work as normal, both in G00 or G01.

I have swapped Nema23 motors - still the same. ie, X axis
I have swapped circuit boards in the controller - still the same; X axis
I have used an earlier copy of Mach3 - installed on another hard drive - still the same.
I have re-installed Mach3 and re-configured the settings - still the same.
I have connected another computer with Mach3 - still the same.
I have changed the parallel port cable to the driver box...

Mach3 has been set to a core frequency of 25kHz. The stepping motors are set at 400 pulses, Velocity down to 1000 and accelaration has been set down to 200 units/sec/sec.

Unless I hold down the shift key, X axis is all over the place...
I have run out of ideas what to do next...

Anyone have an experience with this?

Offline Tweakie.CNC

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Re: Behavioural Changes in Mill
« Reply #1 on: April 25, 2011, 04:19:16 AM »
The symptoms you describe are similar to what would happen if one wire to the stepper motor was disconnected. Although you seem to have checked every possibility already it may be worth checking the wiring again.
The symptom can also be caused by a bad opto isolator (for the X axis direction signal) on the breakout board (if they are socketed then swap two and see if the problem persists).

Hope this helps,

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline pgh3

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Re: Behavioural Changes in Mill
« Reply #2 on: April 25, 2011, 06:33:39 AM »
Thank you for responding, Tweakie,
I'm not very 'into' stepper motor operation, but if a wire were broken, would that explain why is sounds sweet and smooth on a G0 move and rough on a G1 move?

I ask this because I have a control box that takes the LPT1: output from the computer (EPP Parallel port) and with its built in power supply, delivers output to the 3 axes stepper motors and the spindle motor.
I reversed the cables going to the X and Y. The result was the problem was shifted to the Y axis and the X axis ran as though normal, both in G1 and G0 moves.

So maybe the cable to the X axis motor is no good?

Peter

Offline Tweakie.CNC

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Re: Behavioural Changes in Mill
« Reply #3 on: April 25, 2011, 07:09:16 AM »
Hi Peter,

Could be the cable itself or it could be the connector or a soldered joint etc.
The G0 moves are usually much faster than the G1 and this could therefore sound smoother.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline pgh3

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Re: Behavioural Changes in Mill
« Reply #4 on: April 25, 2011, 07:39:37 AM »
Yes! You're a wizard, Tweakie.
It is as you describe! I have found an open circuit in one of the wires in the X axis!

I am actually pleased to find it because I do not like having no confidence in the machine, and this is as good an explanation as I need.
Initial checks show the connections at each end are sound - one is crimped and the other soldered - both ends look fine and professional.
I'll now check the entire cable and look for a  pinch point or sharp bend.

But what a relief to have found the reason.

Many thanks for your help and solution, Tweakie, I'm indebted to you; and to this Forum.

Peter

Offline Tweakie.CNC

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Re: Behavioural Changes in Mill
« Reply #5 on: April 25, 2011, 07:44:41 AM »
Really glad you have found the problem.  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline pgh3

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Re: Behavioural Changes in Mill
« Reply #6 on: April 26, 2011, 04:44:12 PM »
Follow-up:
One of the crimps had actually caused the wire to be severed - it was mechanically held in position enough to make contact, but the slightest movement caused a break.

Replacing the entire cable allowed me to solder all connections and the machine is now up and running once again.

Very satisfying outcome.