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mikie
08-15-2005, 01:50 AM
Hi Guys,

I am getting my machine calibarated in X/Y and Z, but i have come across some concept issues that I was hoping to could be answered.These are Mach 2 related:

Machine setup config:
X-axis is direct drive on a CAM shaft belt
Y-Axis is a 5mm linear screw, direct drive
Z-Axis is a 3mm acme thread, direct drive

When we setup the Z-axis, we used a digital vernier and under >config>Motor tuning set the step per unit until it is accurate.

From what we can see, there is a setting of 5 in the system somewhere.
Is this changeable, or am i missing something.

What I would like to achieve is a better (higher) value for the "steps per unit" figure, or is this only possible wit gearing?

thanks
Michael

Barker806
08-15-2005, 05:34 AM
You are only going to be able to change the set resolution by gearing OR if you have a servo you could change the encoder to a higher resolution. The Direct drive axis is hard to get set just right. I have to sit down every time and run calc's till I am happy with the resolution that the machine will have.

Could you tell a bit more about what you are doing?

Thank you
Brian

mikie
08-15-2005, 06:16 AM
I have managed to get the direct drive within 1 thou. For my application which is to cut model aircraft ribs,etc, this is fine.

I also hope to use this machine, which is really just a prototype, to build aspects of the larger unit.

I also hope to use this machine to get my ability/skill level up on the CAD and CAM systems. If i happen to break something on this unit, oh well too bad.

So the answer seems to be, the value is fixed in the code. Anyone got some source code of Mach 2 by chance, hehe.

/Mike

Barker806
08-17-2005, 06:44 AM
The value is not hard coded but there is a limit to what you can get because of physical limits. For example if you have a drive that works out like this:
1 Thread per inch ball screw (I Know it isa little much) with a stepper driving the screw with a half stepping drive. There are 200 steps per rev of most stepper motors and a Half stepping drive is going to give you a 2x multiplier.
200 steps Per Rev * 2 half stepping / 1 inch per Rev = 400 steps per inch that is a VERY bad resolution of .0025
The 400 would be put in the steps per unit for the motor tuning of that axis.

I hope this gets you what you need....
Brian

ger21
08-17-2005, 08:19 AM
What I would like to achieve is a better (higher) value for the "steps per unit" figure, or is this only possible wit gearing?

thanks
Michael

The "steps per unit" has nothing to do with Mach2/3. It's a real number based on the motors steps/rev, gearing, screw pitch, and a drives microstepping amount. The steps per unit is however many steps it takes to get your machine to move one unit. The only way to change it is by either changing mechanical components, or your drives microstepping value.

The only fixed value in Mach is the top speed, which is limited by the steps/unit and the frequencey your running at, 25, 35, or 45Khz.