holes not center

[Crawler374]

i've looked around and searched, but couldn't find an answer. When i run my program, everything is correct besides the holes. The holes do not center. They are 1/16" off. I know its not my machine because every hole out of 25 are 1/16" off to the left side only. any ideas?

[HuFlungDung]

They are off relative to what? Did you machine the exterior of the part in the same setup and they are off relative to that? Or did you have an error in setting the part datum correctly?

[Crawler374]

for instance, i was miling a square part, with a 1/16" hole in the center. I am using a 1/16" bit, and i knew it didnt look center, so i ran the prgram again, and again, and again with the same results. Then i went back into CAD and re-drew the design, added my machine lines and Gcode, and its doing it again.

[ger21]

Can you post a .dxf and the g-code?

Also, what size bit are you using?

[Crawler374]

its a 1/16" bit.

( Made using CamBam - http://www.cambam.co.uk )
( plate 1/11/2010 9:14:00 PM )
( T0 : 0.062 )
G20 G90 G64 G40
G0 Z0.5
( T0 : 0.062 )
T0 M6
( MOPDrill_1 )
G17
M3 S0
G0 Z0.5
G0 X2.1479 Y2.9974
G81 Z0.125 R0.5 F30.0
G80
( MOPDrill_2 )
S0
G0 Z0.5
G0 X2.15 Y2.5837
G81 Z0.125 R0.5
G80
( MOPDrill_3 )
S0
G0 Z0.5
G0 X2.3009 Y2.1988
G81 Z0.125 R0.5
G80
( MOPDrill_4 )
S0
G0 Z0.5
G0 X4.1693 Y2.9984
G81 Z0.125 R0.5
G80
( MOPDrill_5 )
S0
G0 Z0.5
G0 X4.1693 Y2.5853
G81 Z0.125 R0.5
G80
( MOPDrill_6 )
S0
G0 Z0.5
G0 X4.7521 Y2.3385
G81 Z0.125 R0.5
G80
( MOPProfile_7 )
S0
G0 X4.8284 Y1.9692
G1 Z0.125
G3 F300.0 X4.8319 Y1.969 I0.0034 J0.0308
G3 X4.8586 Y1.9728 I-0.0003 J0.0964
G3 X4.8818 Y1.9834 I-0.0258 J0.0877
G3 X4.9011 Y1.9997 I-0.0495 J0.0779
G3 X4.9157 Y2.0214 I-0.0709 J0.0635
G3 X4.9238 Y2.0458 I-0.0856 J0.0419
G3 X4.9253 Y2.0625 I-0.0905 J0.0168
G1 Y2.4066
G3 Y2.4067 I-0.031 J0.0
G3 X4.9217 Y2.4322 I-0.0927 J-0.0003
G3 X4.9107 Y2.4566 I-0.0921 J-0.0267
G3 X4.8943 Y2.4762 I-0.0798 J-0.0502
G3 X4.873 Y2.4907 I-0.0616 J-0.0679
G3 X4.8482 Y2.4987 I-0.0405 J-0.083
G3 X4.832 Y2.5001 I-0.0167 J-0.0967
G3 X4.8318 I-0.0001 J-0.031
G1 X4.3819
G2 X4.3725 Y2.5014 I0.0001 J0.0341
G2 X4.3651 Y2.5048 I0.0083 J0.0281
G2 X4.3588 Y2.5102 I0.0163 J0.0256
G2 X4.3537 Y2.5178 I0.0249 J0.0222
G2 X4.3508 Y2.5263 I0.0299 J0.0146
G2 X4.3503 Y2.5316 I0.0292 J0.0054
G1 Y3.1252
G3 X4.3193 Y3.1562 I-0.031 J0.0
G1 X4.0193
G3 X3.9883 Y3.1252 I0.0 J-0.031
G1 Y2.4594
G2 X3.987 Y2.451 I-0.0308 J0.0002
G2 X3.9832 Y2.4423 I-0.0326 J0.0094
G2 X3.9775 Y2.4356 I-0.0273 J0.0171
G2 X3.9707 Y2.431 I-0.0198 J0.0218
G2 X3.9626 Y2.4284 I-0.0133 J0.0273
G2 X3.9567 Y2.4278 I-0.0062 J0.0356
G1 X2.3625 Y2.4284
G2 X2.3532 Y2.4298 I0.0001 J0.0341
G2 X2.3458 Y2.4331 I0.0083 J0.0281
G2 X2.3395 Y2.4385 I0.0163 J0.0256
G2 X2.3343 Y2.4461 I0.0249 J0.0222
G2 X2.3315 Y2.4546 I0.0299 J0.0146
G2 X2.331 Y2.46 I0.0292 J0.0054
G1 Y3.1252
G3 X2.3 Y3.1562 I-0.031 J0.0
G1 X2.0
G3 X1.969 Y3.1252 I0.0 J-0.031
G1 Y2.0627
G3 Y2.0626 I0.031 J0.0
G3 X1.9727 Y2.0371 I0.0927 J0.0003
G3 X1.9836 Y2.0127 I0.0921 J0.0267
G3 X2.0 Y1.9931 I0.0798 J0.0502
G3 X2.0213 Y1.9786 I0.0616 J0.0679
G3 X2.0461 Y1.9706 I0.0405 J0.083
G3 X2.0624 Y1.9692 I0.0167 J0.0967
G3 X2.0625 I0.0001 J0.031
G1 X4.8284
G0 Z0.5
M5
M30

[ger21]

What about the .dxf?

[ger21]

The g-code looks centered, if I understand you correctly. Perhaps the tool , or machine is flexing, or you have some backlash?

[Crawler374]

Originally Posted by ger21 The g-code looks centered, if I understand you correctly. Perhaps the tool , or machine is flexing, or you have some backlash?

it is possible. from the naked eye, i dont see much. I will go back and run again to see if i see anything flexing. My backlash is actually pretty good, so i dont think thats it. Thanks Gerry

[HuFlungDung]

Did you spot drill the hole locations to prevent drill wander?

Is your Z axis truly perpendicular to the table? If not, and you have a significant difference in tool length between the mill and the drill, you will suffer some degree of misposition as the head travels in Z, it will displace in X and/or Y.

It is tough to compare a backplot of your gcode to nothing, so I can't tell if the code is correct or not.

[Andre' B]

This is what I get for a plot of the given code.
Edit: I added the 0.062 circles for the drilled holes

[Crawler374]

Originally Posted by HuFlungDung Did you spot drill the hole locations to prevent drill wander? Is your Z axis truly perpendicular to the table? If not, and you have a significant difference in tool length between the mill and the drill, you will suffer some degree of misposition as the head travels in Z, it will displace in X and/or Y. It is tough to compare a backplot of your gcode to nothing, so I can't tell if the code is correct or not.

Originally Posted by Andre' B This is what I get for a plot of the given code. Edit: I added the 0.062 circles for the drilled holes

thank you guys for the help. I actually ran the program and watched the gantry spindle spin and the actual gantry not move. I have exactly 1/16" backlash!!!


thanks for the post, i didn't realize my holes were off center, thanks a lot!