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Mach 3 table size and drawing units confusion
« on: September 05, 2012, 04:58:23 AM »
Hi All

I have been thinking and reading bout this for a while now.
I have read the manual on the home position and re-setting the actual home position to where you want ..offsetting is what they call it i think.

I have a test gcode file that is 237mm wide. When i pull the file into mach, it seems that the size of this object is all the way across the table. My table is like 1,5 meters across by 900 mm in the y axis, so its a pretty big working area.
Now my question : If i load this file, why is it so huge and all across the table width of nearly 1.5 meters when its actually only 237mm wide. I`m obviously missing something..

Thanx guys
Andre

Offline Hood

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Re: Mach 3 table size and drawing units confusion
« Reply #1 on: September 05, 2012, 06:12:50 AM »
If the code is coming out larger than the table size then there can only be a few explanations
1. You have the native units set wrong
2. Code is in different units from setup units but there is no G20 or G21 in the code to tell Mach
3. You have your steps per unit set incorrectly
4 You have a scale set for the axis in question
Hood
Re: Mach 3 table size and drawing units confusion
« Reply #2 on: September 05, 2012, 07:41:30 AM »
Hi

The units in mach is set to mm and my drawing that came out of Cambam is also in mm. So i quess this rules out those possibilities then.
My attention shifts to steps /unit ... i think this will be a good starting point.

Thanx , will give this a looky when i get home

Andre
Re: Mach 3 table size and drawing units confusion
« Reply #3 on: September 06, 2012, 02:30:47 AM »
Hi

The steps/unit was wrong. I just dont have a solid idea of how to get this set correctly yet. I tried the auto setup option on the settings screen, but that didnt fix anything.
What i did here was : You select the axis and then it asks you how far you want it to move. I put 1 into the box . The axis move and then i measure it , which comes to 60 mm. I then put 6 into the box and the axis get set to 33.33333333. It is still too big. I know from playing with the settings , that the smaller the number, the closer the machine gets to the correct size.

So, thinking more about it today i was thinking....... 1 unit in the axis box translates to 60mm when the axis move and i measure it. Should it then be 1/60 = 0.0166666666666667 . This is on both axis.

This makes sense to me, but i havnt tried it yet. Did i math it correctly ? :-\

I also noticed that the velocity and speed settings inputs need to be ridiculously high  ???....in the thousands in order to get the axis to move at a decent speed, because of the small setting input on the steps/unit....the x-axis had a setting of 300 000 when i had the steps/unit set to 1. Now it will be even higher if the steps/unit get set to 0.0166....
Am i on the right path ? ???

Thanx
Andre

Offline Hood

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Re: Mach 3 table size and drawing units confusion
« Reply #4 on: September 06, 2012, 03:01:09 AM »
Using the set steps button relies on your measuring being accurate so my preference is to calculate.
Having said that it would seem you are doing it a strange way, assuming I am understanding what you said.
You tell it to move a distance, Mach moves it and you measure, you then enter the distance you measured. So for your example above it moved 60mm so you enter 60mm and Mach will work out the steps. You entered 6, why I am not sure? That would mean when you asked for a 1mm move it would move 10 as your steps per unit are still out from the previous calculation by a factor of 10.

Hood
Re: Mach 3 table size and drawing units confusion
« Reply #5 on: September 06, 2012, 03:23:36 AM »
When i think about it now, the wheel attathed to the gantry moving the gantry , is about 100mm across. If i need to move the gantry nozzle 1mm, the wheel hardly need to move. I turn of this wheel via the belt , would move the gantry about 60mm as i had it. So it all start to make sense now. ...sometimes i just need to think before i do.

It just a question of getting the move of 1mm to be 1mm and not anything else.

I will try again today and report back.

Andre

Offline RICH

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Re: Mach 3 table size and drawing units confusion
« Reply #6 on: September 06, 2012, 06:57:41 AM »
If you haven't the foggiest idea how to calculate the steps per unit and want to use the axis calibration then:

1. Make a small move, say 25mm
2.It then asks you how far it moved, say it moved 12mm, then that is what you input, Mach will calculate the proper steps based on what you  measured and asks if you want accept the steps per unit, you accept and the steps per unit are changed in tuning.
3. There was probably error in what you measured above, so now make the longest move you can do, say 250 mm
4. Move 250mm, input the actual measured as accurately as you can measure, and again accept

So not knowing anything you made a small move and refined the steps per unit and then made a longer move and minimized the error by making a longer move.

You should calculate the steps as Hood mentioned and then check and refine the steps per unit to account for YOUR systems axis components. Again refining them will only be as accurate as your measurements.

RICH
Re: Mach 3 table size and drawing units confusion
« Reply #7 on: September 10, 2012, 04:32:13 AM »
Hi All

I got it all to work pretty close now !
Looks like the settings is 33.33333333 after all. Last time this didnt work, but i must have commited somewhere to it, and it looks like the movement is pretty close to the correct movement. I will only know once i get the laser focus lens. ...still in the post somewhere..
I got to work on the limit switches and table settings ...i`m getting there slowely.. There is a nice video on home switches and table setup on the forum video section..

Thanx again HOOD and RICH
much appreciated
Andre