Ridges in 3D profiles = hair loss and lots sandpaper

Hey folks

I've got some weirdness going on with the machine and 3D profiling.

Take a look at this:

Attachment 8714

The arrows show the tool path direction along the profile. What I'm getting are ridges that run perpendicular to the step over (ie. if you step over top to bottom, the ridges run left to right). Just to be clear this isn't a step over ridge I'm talking about and something else is going off here.

What could be causing this sort of thing?

I can say this -

• The pattern is consistent and almost looks part of the g-code?
• It doesn't matter which axis you step over in X or Y.
• Also doesn't matter what the profile shape is or the angles involved.
• Its speed independent I've tried 1m/min upto 10m/min and nothing changes.
• I'm using Mach v3.43.66 with Solidcam.

My first first I thought I might have some backlash somewhere but the pattern is very consistent even over a large area with many hundreds of step over passes. I've also ruled out loosing steps as the overall finish piece is as intended and doesn't deviate from the original model. Lost steps would normally be very easy to spot by the end of a large 3D job. No problem with that here.

Hope someone can help.

Ps. There's no jerky movements and machine is smooth whilst running the 3D profile as shown in this vid:

http://www.youtube.com/watch?v=QiE19XZot9g

In picture, right hand side long profile.
You say you are cutting up down and querying the pattern that lies horizontal ?

If I have read this right then the pattern is very regular, in fact it looks cyclic.
One clue would be to measure the ridges and see if the measuremet tied in with say ball screw pitch.

Another thought is that on that profile it will be working Y and Z can you try a sample using X and Z ?

Last thought is to post a section of code that covers one of these passes.
Don't post the whole code we only have until 2020.

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Originally Posted by John S

In picture, right hand side long profile.
You say you are cutting up down and querying the pattern that lies horizontal ?

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Yep exactly that.

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If I have read this right then the pattern is very regular, in fact it looks cyclic.
One clue would be to measure the ridges and see if the measuremet tied in with say ball screw pitch.

Another thought is that on that profile it will be working Y and Z can you try a sample using X and Z ?

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Its working on both. Also in that pic you can see the same pattern on the other face although this is more tightly spaced. Could this have something to do with ball screw pitch as there's more Z movement there and that's 5mm pitch whereas its 10mm on the others?

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ast thought is to post a section of code that covers one of these passes.
Don't post the whole code we only have until 2020.

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Here's a section from the very start of the 3D operation.

Quote:

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N45 G0 G54 X788.686 Y1145.549
N50 G43 H5 Z2.
N55 G0 Z1.93
N60 G1 Z-0.07 F7000
N65 G1 X788.85 Y1146.901 Z-0.259
N70 G1 X788.891 Y1147.24 Z-0.309
N75 G1 X788.932 Y1147.578 Z-0.377
N80 G1 X788.952 Y1147.747 Z-0.418
N85 G1 X788.973 Y1147.916 Z-0.465
N90 G1 X788.993 Y1148.085 Z-0.517
N95 G1 X789.014 Y1148.254 Z-0.575
N100 G1 X789.034 Y1148.423 Z-0.639
N105 G1 X789.055 Y1148.592 Z-0.708
N110 G1 X789.075 Y1148.761 Z-0.783
N115 G1 X789.239 Y1150.114 Z-1.38
N120 G1 X789.26 Y1150.283 Z-1.457
N125 G1 X789.28 Y1150.453 Z-1.54
N130 G1 X789.291 Y1150.537 Z-1.585
N135 G1 X789.301 Y1150.622 Z-1.631
N140 G1 X789.321 Y1150.791 Z-1.728
N145 G1 X789.332 Y1150.875 Z-1.779
N150 G1 X789.342 Y1150.96 Z-1.833
N155 G1 X789.362 Y1151.129 Z-1.946
N160 G1 X789.373 Y1151.213 Z-2.006
N165 G1 X789.383 Y1151.298 Z-2.068
N170 G1 X789.403 Y1151.467 Z-2.199
N175 G1 X789.414 Y1151.552 Z-2.268
N180 G1 X789.547 Y1152.651 Z-3.179
N185 G1 X789.568 Y1152.82 Z-3.32
N190 G1 X789.578 Y1152.904 Z-3.392
N195 G1 X789.588 Y1152.989 Z-3.467
N200 G1 X789.609 Y1153.158 Z-3.625
N205 G1 X789.619 Y1153.243 Z-3.709
N210 G1 X789.624 Y1153.285 Z-3.753
N215 G1 X789.629 Y1153.327 Z-3.797
N220 G1 X789.636 Y1153.387 Z-3.861
N225 G1 X789.644 Y1153.446 Z-3.927
N230 G1 X789.752 Y1154.342 Z-4.931
N235 G1 X789.793 Y1154.68 Z-5.31
N240 G1 X789.814 Y1154.855 Z-5.506
N245 G1 X789.834 Y1155.018 Z-5.69
N250 G1 X789.855 Y1155.187 Z-5.88
N255 G1 X789.875 Y1155.356 Z-6.071
N260 G1 X789.896 Y1155.525 Z-6.263
N265 G1 X789.916 Y1155.694 Z-6.455
N270 G1 X789.937 Y1155.864 Z-6.647
N275 G1 X789.957 Y1156.033 Z-6.84
N280 G1 X789.979 Y1156.213 Z-7.046
N285 G1 X790.06 Y1156.878 Z-7.81
N290 G1 X790.07 Y1156.963 Z-7.907
N295 G1 X790.08 Y1157.047 Z-8.005
N300 G1 X790.101 Y1157.216 Z-8.202
N305 G1 X790.111 Y1157.301 Z-8.302
N310 G1 X790.121 Y1157.385 Z-8.402
N315 G1 X790.142 Y1157.555 Z-8.604
N320 G1 X790.152 Y1157.639 Z-8.706
N325 G1 X790.162 Y1157.724 Z-8.81
N330 G1 X790.409 Y1159.753 Z-11.305
N335 G1 X790.491 Y1160.429 Z-12.137
N340 G1 X790.511 Y1160.598 Z-12.349
N345 G1 X790.696 Y1162.12 Z-14.305

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What happens if you run it at much lower speed? You could be getting bounce back from the material?

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Originally Posted by Swarfing

What happens if you run it at much lower speed? You could be getting bounce back from the material?

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I've played around with the feedrate as low as 1m/min which is as gentle as a mill pond. Same results.

Could it be the material itself and not the cutting process, in other words is it lamination showing through?

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Originally Posted by D.C.

Could it be the material itself and not the cutting process, in other words is it lamination showing through?

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I get the same pattern on both high density polyurethane block, mdf and valchromat so I don't think its the material.

What I'm about to type might be stupid, coming from a person with no CNC experience, but isn't this caused by the movement being done in two steps, rather than simultaneously? so instead of moving say 1/4 step up and 1/4 step left at the same time to get an angled movement, it first does 1/4 step up and later on (scan later?) a 1/4 step left, which results in a step made in the material.

Regards,
dsc.

Since the ridges seem so consistent, they could be part of the original CAD model. For instance if you imported the model into the CAM program as an STL, then that approximates the surface with triangles. If the resolution of the file is insufficient, then you will see the flat surfaces left by the straight line approximations to a curve. Look very carefully at the model imported into the CAM program to see if you can discern any pattern.
Similarly it could be the G-code being generated at too low a resolution, so using lines a few mm long, instead of arcs and lines which are too short to see. It's hard to tell from the code you posted. Can you post a bit from the main profile section, i.e. somewhere in the middle?

Check Jonathan's suggestion.

If you look at the code, there are jumps in the Z.
It starts of with relatively small steps around 0.05 rising to about 0.2, however there are 3 distinct jumps.
Line 110-115 Z moves 0.597, 225-230 it moves 1 and 340-345 it moves 1.965. I know those big moves also correspond with big steps in X and Y, but it does mean the code is a bit inconsistent, and may cause havoc with the projectory planner.