Losing steps

[Edendale]

My Chinese cnc 9060 router has started losing steps in the Y axis,I’ve checked the machine and everything is tight, it’s losing steps at regular intervals almost like it’s built into the software, I’m using Mach 3 and only do 3D carving, not sure where to look next, anyone have any ideas please,29235

[cropwell]

Check the motor wiring! An internal cable break can cause intermittent loss of steps.

[Doddy]

You say regular intervals... is this frequent enough to have confidence that a test should/should not present the problem in a predictable manner?

If your 9060 supports pluggable connectors to the steppers, I'd swap X and Y, and - with due care - run some g-code to present a test engraving that will demonstrate the problem (e.g. repeated iterations of a fixed size square) - any lost steps will present themselves clearly there, and design the g-code to avoid any limits.

If the problem remains on the Y-axis, then I'd follow cropwell's advice.

My thoughts are it's likely to swap with the connector swap - indicating a problem within the controller/computer setup.

If you've got access to a 'scope I'd be examining the signalling going into the stepper driver, just to characterise it... but that's just paranoia on my side due to experience with a previous motion controller.

Edit: Oooer, just noticed the picture (!) - that showing what looks to be a similar number of steps offset on each successive pass in Z?, is there evidence within the rest of the workpiece where the problem is introduced? Is this a problem with a new design, or can you repeat the problem with g-code that previously worked?

[cropwell]

Every time I have had my CNC machine or 3D printer producing strange results on one axis, it has been an internal cable fracture caused by movement of the cable at a flex point. On the CNC that has been the Z axis, on the 3D printer, it has been the X axis because that is the only cable that moves.

[Muzzer]

One simple test to carry out is to check if it returns to the expected Z height at the end of the job. If you've been losing steps along the way, these will most likely accumulate and if you then ask the machine to go to a known Z height at the end of the job, that will be different to what it was when the job started. You could measure Z0 with a test indicator, rehome and then remeasure Z0 perhaps. Both should happen at the same height.

I found this on my Bridgeport conversion. In my case it was due to noise pickup on the wiring which I was able to fix by clipping loads of those ferrite clamp things on the cables. This was during commissioning of my new system. If yours worked fine for ages then started to misbehave, something has changed which could be a different problem. On the other hand, it may have been very marginal all along and something has changed or moved just enough to make it misbehave, such as a cable relaxing or a cable tie failing.

[Neale]

Is this the first time that you have been trying "3dcarving"? There is a fairly common problem where the pulse polarity on the step signal is reversed. The effect is to lose one step every time the direction of that axis changes. If you are doing a lot of fairly simple profile cutting, this will often not show up as a few microsteps here or there doesn't make a big difference. However, once you get to "carving" type operations with lots of reversals, these lost steps add up. The fix is simple - somewhere in the config setup you will probably be able to flip the step signal polarity - and the effect is magical! Well, it was when this happened on my own machine. Muzzer's test will show up this problem.

However, if you have been doing the same kinds of things before without problems, then listen to the other guys!

[Edendale]

On a 700mm x 500mm piece of sapele doing a roughing cut with 8 passes I’m losing 2mm on each pass on the y axis, it only shows itself at the end of the cut but it starts at the right point for the next cut

[Doddy]

but it starts at the right point for the next cut

That statement requires a bit of elaboration.

Do you mean (and I'm possibly mis-interpreting your words here), that for each successive pass, the X/Y recovers to the same position (exactly the same position, no 2mm/pass offset)?

If so, can you post your g-code?

[Edendale]

29248

[Edendale]

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[Edendale]

29250

[Edendale]

Hi Doddy, I might be wrong about it starting again at the same place it’s hard to tell,

[Doddy]

Hi, could you post the g-code as a text-file attachment? (you might need to rename the extension to .txt) The point was to go back to your opening post on this thread to understand if the increasing offset is somehow in the g-code. For that, I/we'd need to look at the first layer and successive layer (differentiated by the plunge-depth on Z) to understand if the resulting displacements in Y were being applied in the g-code... so clearly we need substantial parts of g-code to realise that. Plus, the data reduction that is required is far easier in a macro-supported text editor (or even Excel!), certainly not using an image from a screen shot. HOWEVER, what pushed me to ask for that was your statement that I interpreted as the starting XY on each layer was correct, but the resulting error in Y existed at the end of the layer - as your original analysis concludes that's only really feasible back at the computer/controller/g-code end. But, you've cast doubt on that.

BUT... you could do the donkey work yourself - use an online g-code viewer to confirm that your G-Code is correct (not introducing the Y offsets). If you can confirm that it's largely takes the uncertainty around you situation away, and I'd be more convinced that you're losing steps in the electronics/machine than in the controller. That would NOT be the case if the start-position was correctly recovered on each layer (if the error is in the machine or electronics the offer is cumulative... only recovering if the error cancels itself out).

Every thought I have is to simplify the problem - and for that I'd ask if you've tried to revert to cutting a simple repeatable shape - cut a rectangle 0.5mm deep in a bit of scrap a thoasand times - the thousandth pass should cut the same path as the first. That tells you if the machine is losing steps. ... or the other advice from others earlier in the thread - all good.

[Edendale]

thankyou Doddy for your time on my problem, i have run the program again and it reverts back to the starting point, i will try and send you the code, regards mike.29258