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Author Topic: Set for mm but moving in inches.  (Read 283 times)

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Offline PeteG

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Set for mm but moving in inches.
« on: May 14, 2020, 10:58:47 AM »
Hello

I have been using mach 3 for several months now and had good results. I have a home made machine that moved on the X&Y axis using a timing belt and toothed pulley system. This worked well, but the belt tension was difficult to maintain and sometimes led to poor results, so I have upgraded to a leadscrew system for both axis. This required retuning of the motors. I used the axis calibration in the settings tab and got readings of around 5200, which seems about right and was close to the steps needed on the Z axis which was already on a lead screw system.

I created a test file using Vectric Vcarve to simply make a straight cut 300mm along the X axis, but despite the mach 3 being set to mm in the settings page, G21 being indicated on the program run screen and the Vcarve project being set to mm, the machine moved in inches.

When I first ran the machine after the upgrade I used the automatic axis calculation tool, but this seems to only work in inches. i.e. despite being set to mm, when using MDI a value of X1 this resulted in a movement of 25.4mm i.e. 1 inch, not 1mm. I got the same result whether the units were set to mm or inches.

What is puzzling is that the Z axis also now moves in inches and I had only fine-tuned this axis using the automatic calculation tool.
What have I done wrong?

Cheers

Peter

Offline PeteG

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Re: Set for mm but moving in inches.
« Reply #1 on: May 15, 2020, 11:44:49 AM »
I could really do with some help on this as I can't see why this is happening.

Offline Graham Waterworth

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Re: Set for mm but moving in inches.
« Reply #2 on: May 15, 2020, 04:14:54 PM »
So the pitch of your screws is what?

How many starts on the screws?

Are the motors driving the shaft direct?

What stepping do you have set on the drives?

Is the Mach3 native units set to MM?


My guess is direct drive, 5mm pitch and 1/4 step
« Last Edit: May 15, 2020, 04:39:18 PM by Graham Waterworth »
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Offline PeteG

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Re: Set for mm but moving in inches.
« Reply #3 on: May 16, 2020, 04:25:34 AM »
Hi Graham

Thanks for your reply.

Pitch is 2mm, 4 starts, and you are correct when you say motors are driving the lead screws directly. I'm not sure what you mean by stepping though.

Mach 3 units are set to mm in the 'set native units' drop down and set to mm in the settings tab, this is confirmed by Mach 3 displaying G21 in the top right of the screen. Files are created in Vcarve and are set to mm, and saved to the mm option in the post processor save dialogue, and have G21 at the start of the G code .txt file.

This issue I have is not steps per unit; I set that empirically for the X and Y (the drives that I have changed) and Z has always been on a 2mm pitch, 4 start lead screw with 5120 steps per unit. I set X and Y to this and have made adjustments using the 'axis calibration' option in the settings tab. The issue I have is that now it only moves in inches, even the Z-axis which I haven't changed, only fine tuned with the 'axis calibration' option.

The only thing I am doing differently is that I have been using the MDI page when testing X Y movement. I have found that MDI only seems to work in inches, regardless of settings. i.e. with everything set to mm, an input of X1 in MDI caused a movement of 25.4mm, not 1mm as expected.

On the advice of newfangled solutions, I uninstalled/reinstalled Mach 3, but the issue remains.

Any suggestions?

Regards

Peter

Offline Tweakie.CNC

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Re: Set for mm but moving in inches.
« Reply #4 on: May 16, 2020, 05:20:10 AM »
Hi Peter,

Quote
MDI only seems to work in inches, regardless of settings. i.e. with everything set to mm, an input of X1 in MDI caused a movement of 25.4mm, not 1mm as expected.

Assuming your above measurement is accurate then the simple answer is to return to Motor Tuning and for each axis, divide your existing Steps per Unit by 25.4 and save the changes. Now when you MDI   X1   the axis will move 1mm.

Tweakie.
« Last Edit: May 16, 2020, 05:22:26 AM by Tweakie.CNC »
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Offline PeteG

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Re: Set for mm but moving in inches.
« Reply #5 on: May 16, 2020, 07:32:00 AM »
Hi Tweakie

Thanks for the reply. I tried you suggestion and X1 did indeed move by 1 mm, it took fifteen seconds though. So I reverted back to the original settings, set everything in inches and ran a file that was also in inches and it worked perfectly. But, Mach 3 then displayed an error message - Art 904. I could not find what 904 is, so I clicked the option to correct this. I then got another error message 9991. Clicking to correct this did nothing.

I closed Mach 3 then reopened, made sure everything was still set to inches and ran the same file again. This time, instead of rising 0.5 inch before moving to the start position, it just kept on rising.

Do you know what error code Art 904 is? I can't find any documentation about Mach 3 error codes.

I am confused, and what is most confusing is why the Z axis is not working correctly. I have been using my machine since January without any problems.

 

Offline Tweakie.CNC

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Re: Set for mm but moving in inches.
« Reply #6 on: May 16, 2020, 07:43:00 AM »
Quote
I tried you suggestion and X1 did indeed move by 1 mm, it took fifteen seconds though.

When MDI testing type G0 X1

If necessary return to Motor Tuning and adjust your Velocity and Acceleration settings to set the axis speed then save the changes.



Tweakie.
« Last Edit: May 16, 2020, 07:47:31 AM by Tweakie.CNC »
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Offline Graham Waterworth

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Re: Set for mm but moving in inches.
« Reply #7 on: May 16, 2020, 08:23:43 AM »
The steps per is set in relation to the native units so if your set to mm then your steps will be :-

Assuming your motors are 200 steps per rev. and your drives are set to 1/8 stepping then :-

200 / (2 x 4) = 25 steps / per mm x 1/8 microstep so 25 x 8 will be 200 steps per MM

You then have to set velocity and acceleration for each axis.  On a free moving machine 2500 and 500  may be good starting points.

For inches it will be 200 x (25.4 / (2 x 4)) = 635 x 1/8 microstep so 635 x 8 will be 5080 steps per Inch.

You then have to set velocity and acceleration for each axis.  On a free moving machine 100 and 20 may be good starting points.

These figures can be adjusted until the axis runs reliably without loosing steps.

Or I could be totally wrong.
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Offline PeteG

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Re: Set for mm but moving in inches.
« Reply #8 on: May 16, 2020, 08:55:50 AM »
Thanks everyone, machine is working properly now.

Offline Tweakie.CNC

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Re: Set for mm but moving in inches.
« Reply #9 on: May 16, 2020, 10:07:59 AM »
Excellent news  ;)

Tweakie.
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