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Author Topic: Circles are not round  (Read 9977 times)

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Circles are not round
« on: October 09, 2012, 11:19:35 AM »
Dear all @ Mach 3 Forum,

i was successfully working with this software for some years now, but still there is one question that confuses me.

Because of my converting Process from a different CAD all Cirles will be converted into a pair of semicircles in G-Code.
These Semicircles are not round when milling.
The router is milling two ellipses for each semicircle instead, and of of course the milling Path stopp´s at the end of the first one, then starts to mill the second one and finally stops again were it has started. 

I´ve checked a lot to see were this strange behaivior is produced.
The two ellipses has a perfect coincidence to each other and it´s starting point and End point is congruent  as well. 
All linear movements are really accurate and the repeat accuracy is better then 2/100 mm aprox. 
The Router is Driven by AC Servo Motors and Drive Units by Sanyo and everything is made fom heavy steel.   
The Velocity and Acceleration parameters of the two X and Y motors is set to equal values in Mach3.
Off Course the mechanical inviroment for the X and Y movement is identical.
A Change of the cutting pressure does not change the fact that the router is milling two elipses and not two semicirles instead.

The only reason  I can imagine is that the pulses for driving the X and Y Servos are not send at the same time simultaneously to X and Y Servo Motors.

The servos are driven via the USB-Smooth Stepper, contains the latest software.
Have somebody heard of that the Smooth stepper produces this ?

What cou be wrong with my setup ?
I appreciate every reply
thank you for your ideas

Joerg

Version Mach3: 3.043.022
     

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Re: Circles are not round
« Reply #1 on: October 09, 2012, 12:25:58 PM »
Can you post an example of the circle g code?

Mach3 usually only does what it is told to do.

(;-) TP
Re: Circles are not round
« Reply #2 on: October 09, 2012, 12:55:57 PM »

This is a piece of G code that produces a Semi-Circle for cutting a Round pocket.
The path my router is walking is 2/10 mm out of the ideal.
It seems that the Y Axis is hurry ahead the X one.   
 
( Profil: Mach3 )
G21 G40 G90
G17
S5000 M3
G0 X0.0000 Y0.0000 Z4.0000
M7
X22.6000 Y5.0000 Z4.0000
X22.6000 Y5.0000 Z2.0000
F1080
G1 X22.6000 Y5.0000 Z-0.6380
G2 X17.4000 Y5.0000 Z-0.6380 R2.6000
X22.6000 Y5.0000 Z-0.6380 R2.6000
G1 X21.1600 Y5.0000 Z-0.6380
G2 X18.8400 Y5.0000 Z-0.6380 R1.1600
X21.1600 Y5.0000 Z-0.6380 R1.1600
G0 X21.1600 Y5.0000 Z4.0000
...   

I not have tried drilling holes in a helix. My new CAM is able to generate this.

Thank you Joerg
Re: Circles are not round
« Reply #3 on: October 09, 2012, 06:13:50 PM »
Hi Joerg,
the sanyo servos should bring you good results.
Quote
The Velocity and Acceleration parameters of the two X and Y motors is set to equal values in Mach3.
the acceleration must be set to zero in your drives. the acceleration is done by mach.
the other thing is, your servo system may be bad tuned.
just a thought
Alex
Re: Circles are not round
« Reply #4 on: October 10, 2012, 01:11:20 AM »
Yes ,
I go and check the Servo Setup again.
Another Option is to record the X/Y Pulses with a logic anlyzer while drawing the circle.

J
Re: Circles are not round
« Reply #5 on: October 10, 2012, 04:49:51 AM »
Hi,
your g code looks ok. But the circle is to small and the feedrate to high to test things out.
if you have used a small long endmill it may have bend.
I am shure your problem is a not good tuned servo system / settings or the kinematics
Alex

Re: Circles are not round
« Reply #6 on: October 10, 2012, 05:06:46 AM »
Lets have a look at the servos.
It seems that I not had done any silly mistake somewere else.
I come back to this after further investigation,

J