Specific Print's Acceleration Is Too High!

[BaronWilliams]

Hi,

I've been printing hundreds of things, and suddenly I have a print that is very loud and jerky, and is being printed with layer shifting because it's travel speed acceleration is pretty much instant acceleration, going way faster than the printer can handle. It is super loud like someone hitting a nail on a wall with a hammer. Bang...Bang...Bang...

I thought maybe there's a problem with my printer. So, I tried printing the exact same model using QIDI Print and it prints fine without this issue. So the printer seems to be fine. I prefer to use Simplify3D.

I never had this problem before. I printed other prints after this, and they are all fine, all using the same profile settings. Something about the shape of the object is maybe triggering this instant acceleration on the printer. I have no idea what it is or how to stop it. I attached the model.

I compared the GCODE between Simplify3D and QIDI Print for this print. Simplify3D uses G1 and never uses G0, and QIDI Print is using G0 for moves and G1 for printing. I'm not sure if that is related to the issue. It might be. I don't see anything else that's obviously different between the 2 GCODE outputs. In the GCODE in both, the fastest movement speed is 100 mm/s (F6000). So they are both printing/travelling at the same top speed.

I originally tried reducing travel speed from 280 mm/s (F16800) to 100 mm/s (F6000) and still got the problem. Print speed is 30 mm/s. These settings are fine on all other things I print. I always use a travel speed of 280 mm/s (F16800) on everything, and never saw this problem, until this specific print model.

Is this a know issue with some print models in Simplify3D? Has anyone else experienced this? Does anyone have any idea how to fix it?

EDIT: Additional info. The X/Y belts are tight, and are not slipping. The layer shift is on the Y axis (back to front). The layer shift is consistent for every layer and is the same amount, about 1 mm per layer, and if I rotate the object 90 degrees (Z axis), it rotates the layer shift front to back instead of back to front, always on the Y axis, never on the X axis. If I rotate it 45 degrees (Z axis), it prints perfectly.

[BaronWilliams]

I testing printing the same object with travel speed reduced way down to 50 mm/s (F3000). The print succeeds, but I still hear the banging, it's just not as loud and the force isn't enough to cause layer shifting. It seems that acceleration is still immediate, but now it's slow enough that the printer can deal with it.

If I print it at 100 mm/s (F6000) rotated 45 degrees (Z axis), it is also ok, but I don't hear the banging at all.

What can cause this? Does this mean my printer is starting to fail on the Y axis and this print is simply exacerbating the start of a new Y axis failure gradually occurring on my printer?

If this is a hardware failure that's starting, what could cause this? There are no loose belts. The stepper motor just steps in movement. There is no acceleration built into the stepper motor. It's just a dumb stepper motor doing what the the GCODE/firmware is telling it to do.

I don't understand how this issue is occurring. It seems to me that this can only be a GCODE/firmware issue. Maybe my printer is misinterpreting something in this print telling it to turn off acceleration?

[S3D-Jason]

You could always trying printing a file you had already successfully made in the past without the loud noises. If you now hear the noise with the previously successful file, that might imply it's a hardware problem.

From the slicing side, there re certain shapes that can tend to cause more back and forth movements. For example, if you have a very thin part but you set your infill angle to be perpendicular to that shape, then you will get many short back-and-forth movements. Those can cause more vibration than if you set the infill angle to go parallel with the shape. Do you see any particular areas in the print where that might be happening?

One other idea could be that something has incorrectly increased the acceleration values on the printer. You might want to search the file for errant M204 commands or try setting the acceleration manually in the starting script.

[BaronWilliams]

I have identified the cause of the problem.

The setting Modify travel movements to avoid open spaces is causing it. But only for this particular object model. There's a travel maneuver it makes per layer that my printer does not like. This causes the shift for every layer. If I turn Modify travel movements to avoid open spaces off, then it prints perfectly with an XY Travel Speed set to 280 mm/s.

With Modify travel movements to avoid open spaces enabled, each layer prints perfectly, but gets shifted about 1 mm because of the super fast travel maneuvers it makes before it starts the next layer.

Here's a screen shot showing where the problematic travel maneuvers happen when Modify travel movements to avoid open spaces is enabled. Instead of making straight fast moves, which my printer is fine with, it's performing travel maneuvers that shift direction really fast, and that's the problem. My printer doesn't like that. Acceleration is not taking affect when it shifts direction really fast during the travel move. So this issue is printer specific I guess (QIDI I-fast printer).

The red line from top to bottom in the image is the travel move that causes the problem. Notice the curve near the bottom. My printer is attempting to make that curve travel move at full speed without acceleration for some reason. That direction change is the issue. It's happening at 280 mm/s. It should not do that. It should slow down before it changes direction. But it's not. This is only an issue with travel moves. When printing filament, my printer does this properly.

Screenshot 2025-01-17 184550.png (13.33 KiB) Viewed 747 times

So I have a solution, but I'm not really liking it. This model appears to be highlighting an incompatibility issue with the QIDI I-fast printer and Simplify3D. Simplify3D is assuming that the printer will use acceleration during this travel move with changes in direction, but the QIDI I-fast printer doesn't do this for travel moves with changes in direction and is processing the direction change without acceleration. When printing filament it's fine with this direction change. This is disappointing. I would say this is a printer firmware issue. The same movement works when printing filament, just not when doing a travel move.

[S3D-Jason]

Good investigation! I can't imagine any machine that moves at 200+ mm/sec wouldn't be using acceleration at all, so it's probably more likely the acceleration is just set too high in the firmware. The whole point of acceleration is to prevent steps from skipping when you try to move at the desired speeds, so perhaps the firmware settings just need more adjustment.

Might be worth asking Qidi if the travel acceleration can be adjusted. I seem to remember some older printers had ways of configuring the firmware values using gcode commands.