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Position Errors Only on Diagonal Moves
« Reply #40 on: January 15, 2015, 03:24:14 PM »
Thanks Ray
Ok, I'm curious ....  just 1 more and I'll stay out ..
You've had this machine about a year, and has it ever run any decent parts?


I have been running good parts for a while. My 5 production parts I have been running for close to a year now consist of the following operations:
- drilling
- cleaning up edges of barstock (so a straight line operation that is always parallel to the axes.
- facing

I can still run these production parts without issue and they do GO rapid moves for positioning in 2 axes all the time.

I first noticed the problem when I went to do a production run of a new pat that I have that has a pocketed circle for a bearing. What's interesting is that even though the bearing pocket came out wrong, the rest of the operations (drilling and edge cleanup) came out spot on.



Any diag. interpolated move is trash?
I see it stated where CAM and hand coding does the same.
Did you try a simple point to point rotated square pattern of 4 holes maybe ?
Start at X0,Y0

X1
hole
X0 Y1
hole
X-1 Y0
hole
X0 Y-1
hole

Then measure.

Just wondering if you tried something this simple as a test  ?
This would maybe eliminate some possibilities.
Russ

If I do the program you mention about, it will come out perfect. It's only on G1 moves. G0 moves end up in the right position.

Regards,

Nate


Nate
Fine Line Automation
www.finelineautomation.com
Position Errors Only on Diagonal Moves
« Reply #41 on: January 15, 2015, 03:26:43 PM »
Ray did you measure the Square from corner to corner to check for square or just side to side ??

Have you tried a SIMPLE test with just the basic moves . only one cut, no finish cuts,No offseting , no tool changing etc?

G20 (Units: Inches)
G40 G90 G91.1 G49 G80
F1
(Part: TestSquare)

G0 Z1.000
G00 X0.8839 Y0.0000
G01 Z-0.010 F10.0

X0.0000 Y0.8839 F17.0
X0.8839 Y1.7678
X1.7678 Y0.8839
X0.8839 Y0.0000

G00 Z0.5000
X3.4008 Y0.8839

G01 Z-.010 F10.0
Y0.2589 F17.0
X2.1508
Y1.5089
X3.4008
Y0.8834
G00 Z0.5000
M05 M30

I have tried just a one cut, Simple move hand coded GCode with 0,0 in the center. Still came out the same.

Let me check the square from corner to corner when I get back to the shop.


Nate
Fine Line Automation
www.finelineautomation.com
Re: Position Errors Only on Diagonal Moves
« Reply #42 on: January 15, 2015, 04:32:15 PM »


If I do the program you mention about, it will come out perfect. It's only on G1 moves. G0 moves end up in the right position.

Regards,

Nate


Nate
Fine Line Automation
www.finelineautomation.com

I was assuming G1 for that test.

Really strange :
If you MDI

From 0,0 - G1 X1 Y1 F30

it goes to a different position than ..
 
From 0,0 - G0 X1 Y1

Spindle running, or not makes no difference ? (noise)

Weird

Good luck Gents,
Russ
 :)

Offline BR549

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Re: Position Errors Only on Diagonal Moves
« Reply #43 on: January 15, 2015, 05:16:29 PM »
IF you get a different position from a G00 move as apposed to the same move with G01 then you may have a servo "drive" problem with the TUNING out of wack.

A servo's precision is ONLY as good as it's tuning.

To get to the bottom of it you may have to have a "good" CNC TECH do a bar/bar test on the machine and tune the servos with a scope.

Just a thought, (;-) TP
« Last Edit: January 15, 2015, 05:20:25 PM by BR549 »
Re: Position Errors Only on Diagonal Moves
« Reply #44 on: January 15, 2015, 05:24:22 PM »
Hey TP,
 It seems that the errors would be opposite of what they are if tuning is affecting it.
Correct me if I'm thinking wrongly here.
Seems a slower G1 move would more likely be closer to the code than a full throttle G0 move.
Just seems backwards to me.
Thanks,
Russ

Offline BR549

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Re: Position Errors Only on Diagonal Moves
« Reply #45 on: January 15, 2015, 05:37:53 PM »
acutally it can go either way as the faster move overshoots then rebounds back it may stop short of the target.

It is either a servo drive problem OR table out of square problem. I am thinking servo drive BUT I have been wrong from time to time (;-)

(;-) TP
Position Errors Only on Diagonal Moves
« Reply #46 on: January 15, 2015, 05:55:16 PM »
Some good news logically. The 90 degree squares are not really squares. Here's the corner measurements.




Also, I noticed something else. Look at the edge where the 1.585 is written. It's and the one opposite of it are oblong while the other 2 corners are a normal round.


Nate
Fine Line Automation
www.finelineautomation.com

Offline BR549

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Re: Position Errors Only on Diagonal Moves
« Reply #47 on: January 15, 2015, 07:36:37 PM »
What happens IF you mill a circle ??

Just a thought, (;-)
Position Errors Only on Diagonal Moves
« Reply #48 on: January 15, 2015, 08:06:21 PM »
Some good news logically. The 90 degree squares are not really squares. Here's the corner measurements.




Also, I noticed something else. Look at the edge where the 1.585 is written. It's and the one opposite of it are oblong while the other 2 corners are a normal round.


Nate
Fine Line Automation
www.finelineautomation.com

Some more good news to report.

I ran Hood's test using the 2" square code I ran earlier today with a g4p1 in between each move and slowed the feedrate down to 5 ipm. The square parallel to XY came out right at 2" and measured the same on opposite corners. The 45 degree square was at 1.999 for one side and 2.027" for the other side.  The 2 corner measurements came out the same.

So, can we define it is servos needing tuned?


Nate
Fine Line Automation
www.finelineautomation.com
Re: Position Errors Only on Diagonal Moves
« Reply #49 on: January 15, 2015, 08:33:24 PM »
I wouldn't blame it on the tuning ... until you get whatever is loose corrected, recheck everything mechanical.
The Z slide, spindle bearings/thrust end play, tool holder/drawbar. Something must be loose, that machine is capable of FAR better finishes than that.
Use a prybar and push on every slide in all directions.
I can get better finishes with a hand router.
That's rough, it should be a much better finish.