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Author Topic: Yet another steps per inch post - losing my marbles?  (Read 5020 times)

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Offline Zaae

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Yet another steps per inch post - losing my marbles?
« on: June 11, 2010, 08:23:24 PM »
Hey guys

Ok,
direct drive motors, so no gear reduction.
1.8 degree motors = 200 steps per rev.
10x microstepping = 2000 steps per rev.
8tpi 2 start screws (4tpi effective) = 8000 steps per rev.

This is the part I'm not sure of.

I want  to run metric programs and DRO's, so divide 8000 by 25.4 ?
=========
I set steps per in the mach motor screen to 314.96
EDIT: I also thought maybe it was the rounding, and set it to 314.96062 with the same result.

When I run from zero, to 700 mm, the measurement I get is approximately 1mm farther than it should be.

Am I missing something here?

Thanks :)


EDIT2:

Swiped from another post, but modified to fit my numbers:
4 TPI = 1/4 = 0.25 inch pitch 0.25 x 25.4 = 6.35mm pitch
so
200 steps per rev x 10 micro steps = 2000 steps per rev
1 rev = 6.35mm so 2000/6.35 = 314.96062 steps per mm.

It would appear my way of calculating it came up right too?
« Last Edit: June 11, 2010, 08:36:51 PM by Zaaephod »

Offline ger21

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Re: Yet another steps per inch post - losing my marbles?
« Reply #1 on: June 11, 2010, 08:39:23 PM »
700/701 * 314.96 = 314.511328

Screws have some error, and are rarely what they are supposed to be. Try this number and see if it's better.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Zaae

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Re: Yet another steps per inch post - losing my marbles?
« Reply #2 on: June 11, 2010, 10:22:33 PM »
Thanks, I will give that a shot in the morning, I'm curious how you came up with that number though.

Offline ger21

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Re: Yet another steps per inch post - losing my marbles?
« Reply #3 on: June 12, 2010, 07:06:28 AM »
When you tell it to go 700mm, it goes 701. So you divide 700 by 701, and multiply it by the steps per unit, which should get you what you want.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Zaae

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Re: Yet another steps per inch post - losing my marbles?
« Reply #4 on: June 12, 2010, 12:46:20 PM »
That worked perfectly. I'll need to test it over the entire distance of the table, but it's close enough for today's jobs.

One more question. I've modified my Cycle Start button warn the user of different things to check before the machine starts. It works, but the problem is, I'm using an OEMButton function to "push" cycle start after the code in the script. The downside is, it makes you have to push the button 3 times before it starts. Once to run the code, once to move the gantry to the starting position, and again to actually start the spindle and begin cutting.

I guess the question is, is there a vbscript function that can tell mach3 to do a cycle start, without calling the OEMButton function?

Thanks :)

Offline ger21

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Re: Yet another steps per inch post - losing my marbles?
« Reply #5 on: June 12, 2010, 01:24:47 PM »
I'd change it to use two buttons. Have the cycle start check the conditions, and if OK, run. If not OK, hit the other button to get ready to run.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html