Wrong cutting speed after travel

I’ve been having this issue for a while and have not been able to find the correct setting to change to fix it. When cutting slow (3mm/s) after a long travel it starts to cut really fast and then slows down to the proper speed. The result is that the first part of the cut does not go all the way through. It seems that the longer the travel before the cut starts the faster the cut is when it does start.

I can’ think of anything that would cause this.

The only settings that I know will affect the operation are the min power associated with ‘Start Speed’.

Is this only occurring with very slow cuts?


I am not familiar with your controller but within GRBL controllers, we have $120 and $121 which are parameters that set x and y axis acceleration (and deceleration). I have seen those parameters useful in getting the corners of boxes to burn consistently due to the deceleration that takes place for a direction change. I couldn’t tell for sure from what you described so I’ll assume you are saying that while doing your cutting at 3mm/sec, when a long travel occurs (while in fast travel through white space) the laser cuts too fast when it begins to cut again until eventually slowing down to proper cutting speed where the cut regains good quality. (If I didn’t interpret your issue correctly you can probably disregard the rest of my feedback here…)
Perhaps, your whitespace speed which may be rather high, isn’t decelerating fast enough when it approaches the area to begin cutting again, resulting in the beginning of the new cut area being at a higher speed than desired until the head finishes decelerating to proper cutting speed.
My experience is ONLY with diode lasers so I recognize that I could be totally out in the weeds but I’ve seen things like this with GRBL controllers.

GizmoGuy, This is exactly what is happening.I have a Trocen AWC708C controller.
Idle speed =50
Idle acceleration = 20
Start speed = 5
Cutting acceleration = 20

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Hope this isn’t on deaf ears, but I hope you backed up the ‘factory configuration’ of the controller when you got it or before you ‘tweaked’ anything???

means it’s always done this?

I don’t think this is an issue, but it won’t hurt to try slowing down (or speeding up) the acceleration values. Be aware this effects overscan.

Your values are pretty low, so I doubt that’s the problem.

DSP controllers supposedly use the math algorithms to compute how far something needs to move before it gets to the proper speed, they can also detect a ‘slop’ error this way.

I would think it ‘knows’ it’s speed when it fires, so I’d look for something else. If it’s stepping at a certain rate it should be going a certain speed.

Be aware that when you have min/max power levels that the ‘start speed’ is where the power will start to increase. Anything below that and you will get nothing but min power. When cutting at 3mm/s you will only get min power.

This doesn’t appear to be your problem. It may not be one thing…


Solution: I changed the Idle Acceleration from 20 to 100 mm/sec^2.

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The idle acceleration was only 20 mm/sec^2? That is extremely low for these machines.

Typical acceleration for these is in the range of 2000 to 8000, depending a lot on the hardware. Heavier machines, like a very large format machine with the tube on the X axis might be lower still, and some machines, like an Aeon with a very light engraving head, will use values higher than 20,000.

A generic eBay machine would be in the 4000 mm/sec range.

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This is one of the pitfalls of making your own machine, sometimes hard to find a good starting point. I’ll crank up the accel a little more and see what happens.

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