Axis Configuration Questions

Hi all,

First off my machine works great with linuxcnc. The only question I have is the axisi configuration page. Under the Pulley teeth(Motor:Leadscrew) values what do I put if I have a 10 tooth pulley attached to my motor and no lead screw? is it 10:1? How about the leadscrew pitch? These values would make sense if I have a lead screw attached but I don't.

Also when I'm testing an axis to travel in +1 Inch is would travel 1.25 instead of 1. So I know I have some sort of configuration setup wrong and not a black lash issue because when I stop the test, the (pen) would always head back to where it starts (+/- 2 thou).

I think my next step is to look at the Motor Step /Rev. My motors are 1.8 degree +/- 5 which means it could be either 190 or 210.

Any help would be great.

Thanks

BigJohnT wrote:

1.8 degree is 200 steps per rev.

Is this a belt driven machine?

How far does one rev of the stepper move the axis?

Is your drive using microstepping? if so how many microsteps?

John

Hi John, Thanks for the quick reply. The machine is belt driven for the X and Y axis. The Z is lead screw driven. The Microstepping is 1/16 with hardware switches set correctly. How would I go about to determine the distance for 1 rev? I guess I can mark the tooth and jog the machine 1 full rev...I measure approx 2 inch of distance travel per 1 rev.

Sorry, updated my original post. It goes 1.25" instead of 1 inch...

The 10 tooth pulley is a XL 0.2" pitch.

BigJohnT wrote:

Ok you have 200 steps per rev x16 microsteps = 3200 steps per rev. 1/2 rev = 1" so your scale needs to end up at 1600. So motor pulley/leadscrew pulley is 1:1 and leadscrew = 0.5. This will get you close, however the belt will be stretched a bit so the scale will not be the exact mathematical scale. You will have to measure a move and make small adjustment to your scale.

John

Thanks John,

It seems to be close enough to diddy by trial and error. The only thing is that repeataility is in the +/- 5 thou which is good enough but as I increment by 1 inch, I'm not really getting the measure I want.
ie.
at 1 inch, I'm getting 0.97 repeatable to plus/minus 5 thou.
at 2 inch, I'm getting 2.00 repeatable to plus minus 5 thou. (This one is spot on)
at 3 inch I'm getting 3.01 repeatable to plus minus 5 thou.
at 4 inch I'm getting 4.04 repeatable to plus minus 5 thou.
at 5 inch I'm getting 5.06 repeatable to plus minus 5 thou.

Is this normal? or am I expecting way too much from a home built machine.....

You might want to check for backlash / binding / loose pulley, etc. first.
To check a movement in the positive direction I first go negative, then positive, set my dial indicator at 0, then make a positive move and measure the result, then the same move negative and see it the dial indicator goes back to 0.
so
G1 X-1
G1 X0 ;SET DIAL INDICATOR
G1 X1 ; READ DIAL INDICATOR
G1 X0 ; READ DIAL INDICATOR

Repeat several times.
Then make a bunch of longer moves at different rates and see if at the end the machine returns to the start location to check for missed steps.

Rick G

BigJohnT wrote:

That all depends on the type of belt you used. XL belts are not terribly accurate but fine for most things. You can develop a position compensation table once you get the scale as close as possible.

linuxcnc.org/docs/html/config/ini_config...d_sub_axis_section_a

John

Thanks John, you've been a great help. Aside from all this, what type of belt would you recommend and also what type of motor controller work great with linuxcnc without the hassle?

Rick wrote:

You might want to check for backlash / binding / loose pulley, etc. first.
To check a movement in the positive direction I first go negative, then positive, set my dial indicator at 0, then make a positive move and measure the result, then the same move negative and see it the dial indicator goes back to 0.
so
G1 X-1
G1 X0 ;SET DIAL INDICATOR
G1 X1 ; READ DIAL INDICATOR
G1 X0 ; READ DIAL INDICATOR

Repeat several times.
Then make a bunch of longer moves at different rates and see if at the end the machine returns to the start location to check for missed steps.

Rick G

I just purchased a dial indicator, how to I determine if I can a missing step issue or a backlash issue? Is there different test to determine which?