Z axes raises with a thump sound during 2.5D cut

I am running a long 2.5D cut and at 2 different places there will be a thump noise and the bit will raise up about .25" from what it was set at. I can repeat this by backing up the code and replaying it at that line. I am only cutting purple foam form HD. It does the same thing if I am cutting in air. I tried redoing the code in Aspire and it did the same thing.

I am using Aspire 11.506
Mach4 4.2.0.4809 Build 4809
48X96 Pro
4 HP Spindle
Nema 34

Feed rate 300 Inches/Min
Plunge rate 15
3D raster cut at 40 degrees

G1X39.0612Y14.7695
G1X39.0796Y14.7850Z-0.0183
G1X39.2635Y14.9393Z-0.0185
G1X39.2819Y14.9548Z-0.3138
G1X39.3003Y14.9702Z-0.4000
G1X41.7102Y16.9923Z-0.4000
G1X41.7286Y17.0078Z-0.4400

It always happens at the third line of code as seen here. Also known as line 47492
I’ve only had the machine up and running for a couple months and its been pretty solid on everything else. This is the largest piece I’ve ever carved on it 42x42". When I’m running the 48X96 Pro in the air with the spindle off i can hear a clicking noise whenever the z axes changes direction and I don’t know if that’s normal.

What could be causing this?

When you say it raises up by 0.25", do you mean it goes up when it should go down, or that it fails to go down and then has an offset, or something else?

To reproduce it, do you rewind to line 47490 as shown at the top of your snippet here, or do you rewind some other amount before?

Does the run show any issues prior to the 2 places you mention?

What’s the other line where it also happens? Can you rewind and get consistent unexpected behavior on that one too?

Does it still happen if you dial back the feed rate using the arrows in the lower right of the Mach4 window?

How similar are the files from Aspire and the other program?

I’m curious whether it would do the same thing if you moved the offending section of G-code to its own file and ran that.

Sorry for the barrage, but this really doesn’t make sense to me, so I’m trying to think of ways to gather good and clear data.

Since you mention clicking, maybe read through the few posts in this form about Z-axis issues. Search for Z-axis issues or Z-axis brake.

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When you say it raises up by 0.25", do you mean it goes up when it should go down, or that it fails to go down and then has an offset, or something else?

Answer: It jumps up .25" when it should stay at the level it is already at.

To reproduce it, do you rewind to line 47490 as shown at the top of your snippet here, or do you rewind some other amount before?

Answer: I start at that line. If I start after that line is works fine.

Does the run show any issues prior to the 2 places you mention?

Answer: No

What’s the other line where it also happens? Can you rewind and get consistent unexpected behavior on that one too?

Answer: Yes

Does it still happen if you dial back the feed rate using the arrows in the lower right of the Mach4 window?
Answer: If i dial it back to 75% of the feed rate it gets through that spot

How similar are the files from Aspire and the other program?
Answer: I only use Aspire.

I’m curious whether it would do the same thing if you moved the offending section of G-code to its own file and ran that.
Answer: I will try that.

Sorry for the barrage, but this really doesn’t make sense to me, so I’m trying to think of ways to gather good and clear data.

Since you mention clicking, maybe read through the few posts in this form about Z-axis issues. Search for Z-axis issues or Z-axis brake.

1 Like

Questions:
Does the dro match the g-code?
The 4th line moves the z from -0.0185 to -0.3138. On your machine is a negative z movement up or down? Is this the point where the unwanted movement occurs?
In aspire, do the toolpath traces agree with the observed movement? >> Sometimes tiny, unwanted artifacts will appear in the model. They may not be apparent in the 3d view, but will be reflected in the generated toolpaths.

Check the stepper to ball screw coupler. Make sure its tight and that the spider is still caught in the jaws. Also check that the brake hasn’t worked loose. When the brake comes loose it will make a sound similar to the coupler working itself loose. So a thumping sound every time you reverse direction. The faster the reversal the louder the thump.