tinyg interprets G2/G3 code incorrectly

I have had this problem as well. I am running Firmware .97 and build 440.20. I use Fusion 360 with the stock processor and run in inch mode. I hav found the large circle problem to be intermittent. I have tried going after heat and RF problems with limited success. Yesterday I was able to find a short piece of code the back simulates correctly and fails 100% of the time. It is two holes and the first one just plunges and the second one cuts correctly.

(BRIDGE PINS TEST 3)
(18 STRAIGHT)
(T1 D=0.125 CR=0. – ZMIN=-0.42 – FLAT END MILL)
G0 G90 G94 G17
G20
G53 Z0.
(BIDGE PIN HOLES)
M5
M9
T1
M3 S5000
G54
M8
G0 X1.4957 Y-1.6119
Z0.6
Z0.0187
G1 Z-0.0613 F10.
X1.4988 Y-1.6065
G3 X1.4741 Y-1.65 Z-0.081 I-0.0124 J-0.0217 F20.
X1.4988 Y-1.6065 Z-0.1007 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1204 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.1401 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1598 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.1794 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1991 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2188 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.2385 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2582 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.2779 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2976 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.3172 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.3369 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.3566 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.3763 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.396 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.4157 I0.0124 J0.0217
X1.4821 Y-1.6036 Z-0.42 I-0.0124 J-0.0217
X1.4908 Y-1.6528 I0.0043 J-0.0246
X1.4821 Y-1.6036 I-0.0043 J0.0246
G1 X1.4832 Y-1.6098 F10.
G0 Z0.2
X1.925 Y-1.535
Z0.0246
G1 Z-0.0554 F10.
X1.9312
G3 X1.8812 Z-0.0751 I-0.025 J0. F20.
X1.9312 Z-0.0947 I0.025 J0.
X1.8812 Z-0.1144 I-0.025 J0.
X1.9312 Z-0.1341 I0.025 J0.
X1.8812 Z-0.1538 I-0.025 J0.
X1.9312 Z-0.1735 I0.025 J0.
X1.8812 Z-0.1932 I-0.025 J0.
X1.9312 Z-0.2129 I0.025 J0.
X1.8812 Z-0.2325 I-0.025 J0.
X1.9312 Z-0.2522 I0.025 J0.
X1.8812 Z-0.2719 I-0.025 J0.
X1.9312 Z-0.2916 I0.025 J0.
X1.8812 Z-0.3113 I-0.025 J0.
X1.9312 Z-0.331 I0.025 J0.
X1.8812 Z-0.3507 I-0.025 J0.
X1.9312 Z-0.3703 I0.025 J0.
X1.8812 Z-0.39 I-0.025 J0.
X1.9312 Z-0.4097 I0.025 J0.
X1.9044 Y-1.5101 Z-0.42 I-0.025 J0.
X1.908 Y-1.5599 I0.0018 J-0.0249
X1.9044 Y-1.5101 I-0.0018 J0.0249
G1 X1.9049 Y-1.5163 F10.
G0 Z0.2

I have also tried switching the cut from climb o conventional to force the G2 code with no luck: (The first hole is a plunge and the second hole is a helix.)

(TRAVEL GUITAR 18)
(18 STRAIGHT)
(T1 D=0.125 CR=0. – ZMIN=-0.42 – FLAT END MILL)
G0 G90 G94 G17
G20
G53 Z0.

(BIDGE PIN HOLES)
M5
M9
T1
M3 S5000
G54
M8
G0 X1.4725 Y-1.6275
Z0.6
Z0.0187
G1 Z-0.0488 F10.
X1.4726 Y-1.6272 Z-0.0516
X1.4731 Y-1.6264 Z-0.0543
X1.4738 Y-1.6251 Z-0.0566
X1.4748 Y-1.6234 Z-0.0586
X1.476 Y-1.6213 Z-0.0601
X1.4773 Y-1.619 Z-0.061
X1.4787 Y-1.6166 Z-0.0613
X1.4817 Y-1.6112
G2 X1.4988 Y-1.6065 I0.0109 J-0.0062
X1.4741 Y-1.65 Z-0.081 I-0.0124 J-0.0217 F20.
X1.4988 Y-1.6065 Z-0.1007 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1204 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.1401 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1598 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.1794 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.1991 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2188 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.2385 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2582 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.2779 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.2976 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.3172 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.3369 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.3566 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.3763 I0.0124 J0.0217
X1.4741 Y-1.65 Z-0.396 I-0.0124 J-0.0217
X1.4988 Y-1.6065 Z-0.4157 I0.0124 J0.0217
X1.5098 Y-1.6194 Z-0.42 I-0.0124 J-0.0217
X1.4631 Y-1.6371 I-0.0234 J-0.0089
X1.5098 Y-1.6194 I0.0234 J0.0089
X1.5026 Y-1.6355 I-0.0117 J-0.0044 F10.
G1 X1.4967 Y-1.6377
X1.4941 Y-1.6387 Z-0.4197
X1.4916 Y-1.6396 Z-0.4188
X1.4894 Y-1.6405 Z-0.4173
X1.4876 Y-1.6412 Z-0.4153
X1.4862 Y-1.6417 Z-0.4129
X1.4853 Y-1.642 Z-0.4103
X1.485 Y-1.6421 Z-0.4075
G0 Z0.2
X1.9 Y-1.5225
Z0.0246
G1 Z-0.0429 F10.
G18 G3 X1.9125 Z-0.0554 I0.0125 K0.
G1 X1.9187
G17 G2 X1.9312 Y-1.535 I0. J-0.0125
X1.8812 Z-0.0751 I-0.025 J0. F20.
X1.9312 Z-0.0947 I0.025 J0.
X1.8812 Z-0.1144 I-0.025 J0.
X1.9312 Z-0.1341 I0.025 J0.
X1.8812 Z-0.1538 I-0.025 J0.
X1.9312 Z-0.1735 I0.025 J0.
X1.8812 Z-0.1932 I-0.025 J0.
X1.9312 Z-0.2129 I0.025 J0.
X1.8812 Z-0.2325 I-0.025 J0.
X1.9312 Z-0.2522 I0.025 J0.
X1.8812 Z-0.2719 I-0.025 J0.
X1.9312 Z-0.2916 I0.025 J0.
X1.8812 Z-0.3113 I-0.025 J0.
X1.9312 Z-0.331 I0.025 J0.
X1.8812 Z-0.3507 I-0.025 J0.
X1.9312 Z-0.3703 I0.025 J0.
X1.8812 Z-0.39 I-0.025 J0.
X1.9312 Z-0.4097 I0.025 J0.
X1.9044 Y-1.5599 Z-0.42 I-0.025 J0.
X1.908 Y-1.5101 I0.0018 J0.0249
X1.9044 Y-1.5599 I-0.0018 J-0.0249
X1.8928 Y-1.5466 I0.0009 J0.0125 F10.
G1 X1.8933 Y-1.5403
X1.8935 Y-1.5376 Z-0.4197
X1.8937 Y-1.5349 Z-0.4188
X1.8939 Y-1.5326 Z-0.4173
X1.894 Y-1.5306 Z-0.4153
X1.8941 Y-1.5291 Z-0.4129
X1.8942 Y-1.5282 Z-0.4103
Y-1.5279 Z-0.4075
G0 Z0.2
X2.3197 Y-1.4293
Z0.0245

My problem seems to be in the 4 digits of precision in the j parameter. I edited the code to be only 3 digits and it is boring the holes correctly. I think it will resolve issue 181:

https://github.com/synthetos/TinyG/issues/181

Changing the post processor code in Fusion 360 to:

var xyzFormat = createFormat({decimals:3, forceDecimal:true});
var rFormat = xyzFormat; // radius
var abcFormat = createFormat({decimals:3, forceDecimal:true, scale:DEG});
var feedFormat = createFormat({decimals:(unit == MM ? 0 : 1), forceDecimal:true});

The solution is to change the tinyg postprocessor. In fusion 360, here are the modifications that I did:

replace the following line

allowedCircularPlanes = 1 << PLANE_XY;

by this line:

allowedCircularPlanes = (0 << PLANE_XY) | (0 << PLANE_ZX) | (0 << PLANE_YZ);

It will fix your problems.

The TinyG post files simply define the value of this variable and never uses it, so I assume that it is used by the overall g-code processor to change its behavior.

In practice, I have compared gcode files; with this change, it generates a very long list of straight lines. Without the change, it issues a simple G2 or G3 command.

I did not come up with the solution (obviously!), read it elsewhere. The issue was described as the Arduino does not have sufficient processing power to compute the arcs on time, thus mangling the path occasionally. From my experience, the “defect” where very reproducible (e.g. the 6th and 7th pockets in a long list). Never had any issues after.

Note that in Fusion 360, they updates the post from time to time. You will have to reapply this patch occasionally to their latest TinyG version.

I had Fusion update their post processor. It is now the default to not post arcs. I have a few post processors that I use. The new stock one, the old stock one and an old one the only uses mm. I find the problem is arcs in inches but I can’t prove it.

Is there enough memory to split the math into parts to remedy the rounding errors? Or is that just asking too much of the tinyG?

Just Spitballing:
There is an expansion ‘slot’ set aside for an additional TinyG connection–and I know that it’s impossible to time the drivers to accurately do 6-axis machining, but could we utilize a ‘driverless’ TinyG to help with the math? Maybe a pre-processor to offload some of the work and let the downstream TinyG do the actual driving with the the first pass?

• This reply was modified 6 years ago by Vex.