Uneven finish

[orbyog]

Hello, I am having a problem when cutting a dome or 3d relief. It is adding small lines or ripples (not stepover) perpendicular to the cut direction eg: if rastering in X the lines appear in the Y direction and vise versa, they also appear in offset cut as well.
I have tried differnet computers, different versions of Mach3 and Smooth Stepper plug ins & drivers (last two). Also gcode from Artcam and Aspire in three different output types.
The only conclusion I can come up with is the Smooth Stepper as this hadn"t happened using the printer port. Please let me know if you need anymore info or would like the XML & Gcode files for review.
It's not vibration or chattering, also ran code first at 180ipm then at 120,100,80,60,30ipm all with the same result. It does appear more pronounced the larger the job size. I was testing using an 18 degree dome 4"Y 6"X about .125 high with a .125 ballnose with 6% steppover. Also Tried enabling and disabling CV settings all with the same result.
Thanks Robert

(Not sure if this is in the correct place, Moderator feel free to move)

[orbyog]

Nobody has ANY ideas or recomendations?
Warp9 recommended reversing the polarity for the step signal, but that didn't help. I have attached a crude and exaggerated drawing.... The "bumps or lines" are only about .003"

[fatal-exception]

Can you physically see the z axis move up where the lines are appearing?

Maybe it's a mechanical problem like a warped ball screw?

Do you have any pictures of the problem?

Paul

[orbyog]

Thanks for the input, I put a dial indicator on and jogged up and down and the screw seems fine. I added a drawing above, a picture doesn't really show as it's only about .003" which also answers I don't notice the axis moving but can see on the finished product.

[BobWarfield]

That's very bizarre. I would try a post over on the Mach3 boards. It sounds like you're pretty convinced it is a controller problem of some kind. Now you have to figure out if it is Mach3 or Smoothstepper.

Have you completely ruled out the possibility your CAM program is doing something strange?

Cheers,

BW

[orbyog]

Thanks Bob, I haven't ruled anything out at this point. I can't conceive how it could be anything mechanical as it is so perfectly contoured, loose spindle or guide, backlash, etc. would give a more irratic behavior I would imagine. CAM was the first place I looked but as far as I can tell the Gcode looks good but I am no expert. Heres a sample of code:

T1M6
G17
G0Z0.9862
G0X0.0000Y0.0000S12000M3
G0X-0.3003Y-2.2879Z0.2362
G1Z-0.1120F60.0
G1X0.2257Z-0.1117F180.0
X0.3282Y-2.2875Z-0.1120
X0.4864Y-2.2804Z-0.1120
X-0.0278Z-0.1107
X-0.4775Y-2.2801Z-0.1120
X-0.5935Y-2.2729Z-0.1120
X-0.0792Z-0.1100
X0.4544Z-0.1110
X0.6087Z-0.1120
X0.7104Y-2.2654Z-0.1120
X0.1969Z-0.1094
X-0.3294Z-0.1099
X-0.6952Z-0.1120
X-0.7839Y-2.2579Z-0.1121
X-0.2627Z-0.1090
X0.2586Z-0.1089
X0.7798Z-0.1119
X0.8034Y-2.2576Z-0.1121
X0.8764Y-2.2504Z-0.1120
X0.3616Z-0.1084
X-0.1662Z-0.1079
X-0.6875Z-0.1105
X-0.8613Z-0.1120
X-0.9332Y-2.2429Z-0.1120
X-0.4259Z-0.1080
X0.1071Z-0.1070
X0.6273Z-0.1091
X0.9484Z-0.1119
X1.0160Y-2.2354Z-0.1120
X0.5021Z-0.1076
X-0.0181Z-0.1063
X-0.5512Z-0.1080
X-1.0008Z-0.1120
X-1.0618Y-2.2279Z-0.1120

[rowbare]

Does the shape come out properly or does it look as though you are missing steps?
Can you try it again using the parallel port? Preferably on the same computer.
Have you ruled out any mechanical issues? It almost sounds as though there is play in the Z coupler where the motor raises the spindle and then the screw unwinds and drops the spindle down a hair.

Oops you posted again while I had the window open....

bob

[ger21]

Can you post a picture?

[Robski]

Can you run over the surface again with no change in settings and look at the changes?

[samco]

is this a stepper machine? How many thousands per full step of the stepping motor?

sam

[dertsap]

i had a similar issue on my first machine build , the y screw was running off center ever so slightly and it would bounce the z assembly a thou or two , it was easy to tell on mine because the lines on the parts matched up with the pitch of the screw

[orbyog]

Thanks for all the great ideas, I will be investigating this further this weekend. First by removing the smooth stepper from the equation. I'm not going to dismiss any idea no matter how unlikely I "think" it maybe. I will post back tomorrow with any updates. Thanks again for the input.
Robert